Apache Module mod_ssl

Description:Strong cryptography using the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols
Status:Extension
Module Identifier:ssl_module
Source File:mod_ssl.c

Summary

This module provides SSL v3 and TLS v1.x support for the Apache HTTP Server. SSL v2 is no longer supported.

This module relies on OpenSSL to provide the cryptography engine.

Further details, discussion, and examples are provided in the SSL documentation.

Environment Variables

This module can be configured to provide several items of SSL information as additional environment variables to the SSI and CGI namespace. This information is not provided by default for performance reasons. (See SSLOptions StdEnvVars, below.) The generated variables are listed in the table below. For backward compatibility the information can be made available under different names, too. Look in the Compatibility chapter for details on the compatibility variables.

Variable Name:Value Type:Description:
HTTPSflagHTTPS is being used.
SSL_PROTOCOLstringThe SSL protocol version (SSLv3, TLSv1, TLSv1.1, TLSv1.2)
SSL_SESSION_IDstringThe hex-encoded SSL session id
SSL_SESSION_RESUMEDstringInitial or Resumed SSL Session. Note: multiple requests may be served over the same (Initial or Resumed) SSL session if HTTP KeepAlive is in use
SSL_SECURE_RENEGstringtrue if secure renegotiation is supported, else false
SSL_CIPHERstringThe cipher specification name
SSL_CIPHER_EXPORTstringtrue if cipher is an export cipher
SSL_CIPHER_USEKEYSIZEnumberNumber of cipher bits (actually used)
SSL_CIPHER_ALGKEYSIZEnumberNumber of cipher bits (possible)
SSL_COMPRESS_METHODstringSSL compression method negotiated
SSL_VERSION_INTERFACEstringThe mod_ssl program version
SSL_VERSION_LIBRARYstringThe OpenSSL program version
SSL_CLIENT_M_VERSIONstringThe version of the client certificate
SSL_CLIENT_M_SERIALstringThe serial of the client certificate
SSL_CLIENT_S_DNstringSubject DN in client's certificate
SSL_CLIENT_S_DN_ x509stringComponent of client's Subject DN
SSL_CLIENT_SAN_Email_ nstringClient certificate's subjectAltName extension entries of type rfc822Name
SSL_CLIENT_SAN_DNS_ nstringClient certificate's subjectAltName extension entries of type dNSName
SSL_CLIENT_SAN_OTHER_msUPN_ nstringClient certificate's subjectAltName extension entries of type otherName, Microsoft User Principal Name form (OID 1.3.6.1.4.1.311.20.2.3)
SSL_CLIENT_I_DNstringIssuer DN of client's certificate
SSL_CLIENT_I_DN_ x509stringComponent of client's Issuer DN
SSL_CLIENT_V_STARTstringValidity of client's certificate (start time)
SSL_CLIENT_V_ENDstringValidity of client's certificate (end time)
SSL_CLIENT_V_REMAINstringNumber of days until client's certificate expires
SSL_CLIENT_A_SIGstringAlgorithm used for the signature of client's certificate
SSL_CLIENT_A_KEYstringAlgorithm used for the public key of client's certificate
SSL_CLIENT_CERTstringPEM-encoded client certificate
SSL_CLIENT_CERT_CHAIN_ nstringPEM-encoded certificates in client certificate chain
SSL_CLIENT_CERT_RFC4523_CEAstringSerial number and issuer of the certificate. The format matches that of the CertificateExactAssertion in RFC4523
SSL_CLIENT_VERIFYstringNONE , SUCCESS , GENEROUS or FAILED: reason
SSL_SERVER_M_VERSIONstringThe version of the server certificate
SSL_SERVER_M_SERIALstringThe serial of the server certificate
SSL_SERVER_S_DNstringSubject DN in server's certificate
SSL_SERVER_SAN_Email_ nstringServer certificate's subjectAltName extension entries of type rfc822Name
SSL_SERVER_SAN_DNS_ nstringServer certificate's subjectAltName extension entries of type dNSName
SSL_SERVER_SAN_OTHER_dnsSRV_ nstringServer certificate's subjectAltName extension entries of type otherName, SRVName form (OID 1.3.6.1.5.5.7.8.7, RFC 4985)
SSL_SERVER_S_DN_ x509stringComponent of server's Subject DN
SSL_SERVER_I_DNstringIssuer DN of server's certificate
SSL_SERVER_I_DN_ x509stringComponent of server's Issuer DN
SSL_SERVER_V_STARTstringValidity of server's certificate (start time)
SSL_SERVER_V_ENDstringValidity of server's certificate (end time)
SSL_SERVER_A_SIGstringAlgorithm used for the signature of server's certificate
SSL_SERVER_A_KEYstringAlgorithm used for the public key of server's certificate
SSL_SERVER_CERTstringPEM-encoded server certificate
SSL_SRP_USERstringSRP username
SSL_SRP_USERINFOstringSRP user info
SSL_TLS_SNIstringContents of the SNI TLS extension (if supplied with ClientHello)

x509 specifies a component of an X.509 DN; one of C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email . In httpd 2.2.0 and later, x509 may also include a numeric _n suffix. If the DN in question contains multiple attributes of the same name, this suffix is used as a zero-based index to select a particular attribute. For example, where the server certificate subject DN included two OU attributes, SSL_SERVER_S_DN_OU_0 and SSL_SERVER_S_DN_OU_1 could be used to reference each. A variable name without a _n suffix is equivalent to that name with a _0 suffix; the first (or only) attribute. When the environment table is populated using the StdEnvVars option of the SSLOptions directive, the first (or only) attribute of any DN is added only under a non-suffixed name; i.e. no _0 suffixed entries are added.

In httpd 2.4.32 and later, an optional _RAW suffix may be added to x509 in a DN component, to suppress conversion of the attribute value to UTF-8. This must be placed after the index suffix (if any). For example, SSL_SERVER_S_DN_OU_RAW or SSL_SERVER_S_DN_OU_0_RAW could be used.

The format of the *_DN variables has changed in Apache HTTPD 2.3.11. See the LegacyDNStringFormat option for SSLOptions for details.

SSL_CLIENT_V_REMAIN is only available in version 2.1 and later.

A number of additional environment variables can also be used in SSLRequire expressions, or in custom log formats:

HTTP_USER_AGENT        PATH_INFO             AUTH_TYPE
HTTP_REFERER           QUERY_STRING          SERVER_SOFTWARE
HTTP_COOKIE            REMOTE_HOST           API_VERSION
HTTP_FORWARDED         REMOTE_IDENT          TIME_YEAR
HTTP_HOST              IS_SUBREQ             TIME_MON
HTTP_PROXY_CONNECTION  DOCUMENT_ROOT         TIME_DAY
HTTP_ACCEPT            SERVER_ADMIN          TIME_HOUR
THE_REQUEST            SERVER_NAME           TIME_MIN
REQUEST_FILENAME       SERVER_PORT           TIME_SEC
REQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAY
REQUEST_SCHEME         REMOTE_ADDR           TIME
REQUEST_URI            REMOTE_USER

In these contexts, two special formats can also be used:

  • ENV:variablename
    This will expand to the standard environment variable variablename.

  • HTTP:headername
    This will expand to the value of the request header with name headername.

Custom Log Formats

When mod_ssl is built into Apache or at least loaded (under DSO situation) additional functions exist for the Custom Log Format of mod_log_config. First there is an additional `` %{ varname }x '' eXtension format function which can be used to expand any variables provided by any module, especially those provided by mod_ssl which can you find in the above table.

For backward compatibility there is additionally a special `` %{ name }c '' cryptography format function provided. Information about this function is provided in the Compatibility chapter.

Example

CustomLog "logs/ssl_request_log" "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

These formats even work without setting the StdEnvVars option of the SSLOptions directive.

Request Notes

mod_ssl sets "notes" for the request which can be used in logging with the %{name}n format string in mod_log_config.

The notes supported are as follows:

  • ssl-access-forbidden
    This note is set to the value 1 if access was denied due to an SSLRequire or SSLRequireSSL directive.

  • ssl-secure-reneg
    If mod_ssl is built against a version of OpenSSL which supports the secure renegotiation extension, this note is set to the value 1 if SSL is in used for the current connection, and the client also supports the secure renegotiation extension. If the client does not support the secure renegotiation extension, the note is set to the value 0. If mod_ssl is not built against a version of OpenSSL which supports secure renegotiation, or if SSL is not in use for the current connection, the note is not set.

Expression Parser Extension

When mod_ssl is built into Apache or at least loaded (under DSO situation) any variables provided by mod_ssl can be used in expressions for the ap_expr Expression Parser. The variables can be referenced using the syntax `%{` varname `}` ''. Starting with version 2.4.18 one can also use the [mod_rewrite](mod-mod_rewrite.html) style syntax %{SSL: varname } '' or the function style syntax `` ssl( varname ) ''.

Example (using mod_headers)

Header set X-SSL-PROTOCOL "expr=%{SSL_PROTOCOL}"
Header set X-SSL-CIPHER "expr=%{SSL:SSL_CIPHER}"

This feature even works without setting the StdEnvVars option of the SSLOptions directive.

Authorization providers for use with Require

mod_ssl provides a few authentication providers for use with mod_authz_core's Require directive.

Require ssl

The ssl provider denies access if a connection is not encrypted with SSL. This is similar to the SSLRequireSSL directive.

Require ssl

Require ssl-verify-client

The ssl provider allows access if the user is authenticated with a valid client certificate. This is only useful if SSLVerifyClient optional is in effect.

The following example grants access if the user is authenticated either with a client certificate or by username and password.

Require ssl-verify-client
Require valid-user

SSLCACertificateFile Directive

Description:File of concatenated PEM-encoded CA Certificates for Client Auth
Syntax:SSLCACertificateFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive sets the all-in-one file where you can assemble the Certificates of Certification Authorities (CA) whose clients you deal with. These are used for Client Authentication. Such a file is simply the concatenation of the various PEM-encoded Certificate files, in order of preference. This can be used alternatively and/or additionally to SSLCACertificatePath.

Example

SSLCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-client.crt"

SSLCACertificatePath Directive

Description:Directory of PEM-encoded CA Certificates for Client Auth
Syntax:SSLCACertificatePath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive sets the directory where you keep the Certificates of Certification Authorities (CAs) whose clients you deal with. These are used to verify the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through hash filenames. So usually you can't just place the Certificate files there: you also have to create symbolic links named hash-value .N . And you should always make sure this directory contains the appropriate symbolic links.

Example

SSLCACertificatePath "/usr/local/apache2/conf/ssl.crt/"

SSLCADNRequestFile Directive

Description:File of concatenated PEM-encoded CA Certificates for defining acceptable CA names
Syntax:SSLCADNRequestFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

When a client certificate is requested by mod_ssl, a list of acceptable Certificate Authority names is sent to the client in the SSL handshake. These CA names can be used by the client to select an appropriate client certificate out of those it has available.

If neither of the directives SSLCADNRequestPath or SSLCADNRequestFile are given, then the set of acceptable CA names sent to the client is the names of all the CA certificates given by the SSLCACertificateFile and SSLCACertificatePath directives; in other words, the names of the CAs which will actually be used to verify the client certificate.

In some circumstances, it is useful to be able to send a set of acceptable CA names which differs from the actual CAs used to verify the client certificate - for example, if the client certificates are signed by intermediate CAs. In such cases, SSLCADNRequestPath and/or SSLCADNRequestFile can be used; the acceptable CA names are then taken from the complete set of certificates in the directory and/or file specified by this pair of directives.

SSLCADNRequestFile must specify an all-in-one file containing a concatenation of PEM-encoded CA certificates.

Example

SSLCADNRequestFile "/usr/local/apache2/conf/ca-names.crt"

SSLCADNRequestPath Directive

Description:Directory of PEM-encoded CA Certificates for defining acceptable CA names
Syntax:SSLCADNRequestPath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This optional directive can be used to specify the set of acceptable CA names which will be sent to the client when a client certificate is requested. See the SSLCADNRequestFile directive for more details.

The files in this directory have to be PEM-encoded and are accessed through hash filenames. So usually you can't just place the Certificate files there: you also have to create symbolic links named hash-value .N . And you should always make sure this directory contains the appropriate symbolic links.

Example

SSLCADNRequestPath "/usr/local/apache2/conf/ca-names.crt/"

SSLCARevocationCheck Directive

Description:Enable CRL-based revocation checking
Syntax:SSLCARevocationCheck chain\|leaf\|none [flags ...]
Default:SSLCARevocationCheck none
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Optional flags available in httpd 2.4.21 or later

Enables certificate revocation list (CRL) checking. At least one of SSLCARevocationFile or SSLCARevocationPath must be configured. When set to chain (recommended setting), CRL checks are applied to all certificates in the chain, while setting it to leaf limits the checks to the end-entity cert.

The available flags are:

  • no_crl_for_cert_ok
    Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when no CRL(s) for the checked certificate(s) were found in any of the locations configured with SSLCARevocationFile or SSLCARevocationPath.

With the introduction of SSLCARevocationFile , the behavior has been changed: by default with chain or leaf , CRLs must be present for the validation to succeed - otherwise it will fail with an "unable to get certificate CRL" error.

The flag no_crl_for_cert_ok allows to restore previous behaviour.

Example

SSLCARevocationCheck chain

Compatibility with versions 2.2

SSLCARevocationCheck chain no_crl_for_cert_ok

SSLCARevocationFile Directive

Description:File of concatenated PEM-encoded CA CRLs for Client Auth
Syntax:SSLCARevocationFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive sets the all-in-one file where you can assemble the Certificate Revocation Lists (CRL) of Certification Authorities (CA) whose clients you deal with. These are used for Client Authentication. Such a file is simply the concatenation of the various PEM-encoded CRL files, in order of preference. This can be used alternatively and/or additionally to SSLCARevocationPath.

Example

SSLCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-client.crl"

SSLCARevocationPath Directive

Description:Directory of PEM-encoded CA CRLs for Client Auth
Syntax:SSLCARevocationPath directory-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive sets the directory where you keep the Certificate Revocation Lists (CRL) of Certification Authorities (CAs) whose clients you deal with. These are used to revoke the client certificate on Client Authentication.

The files in this directory have to be PEM-encoded and are accessed through hash filenames. So usually you have not only to place the CRL files there. Additionally you have to create symbolic links named hash-value .rN . And you should always make sure this directory contains the appropriate symbolic links.

Example

SSLCARevocationPath "/usr/local/apache2/conf/ssl.crl/"

SSLCertificateChainFile Directive

Description:File of PEM-encoded Server CA Certificates
Syntax:SSLCertificateChainFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

SSLCertificateChainFile is deprecated

SSLCertificateChainFile became obsolete with version 2.4.8, when SSLCertificateFile was extended to also load intermediate CA certificates from the server certificate file.

This directive sets the optional all-in-one file where you can assemble the certificates of Certification Authorities (CA) which form the certificate chain of the server certificate. This starts with the issuing CA certificate of the server certificate and can range up to the root CA certificate. Such a file is simply the concatenation of the various PEM-encoded CA Certificate files, usually in certificate chain order.

This should be used alternatively and/or additionally to SSLCACertificatePath for explicitly constructing the server certificate chain which is sent to the browser in addition to the server certificate. It is especially useful to avoid conflicts with CA certificates when using client authentication. Because although placing a CA certificate of the server certificate chain into SSLCACertificatePath has the same effect for the certificate chain construction, it has the side-effect that client certificates issued by this same CA certificate are also accepted on client authentication.

But be careful: Providing the certificate chain works only if you are using a single RSA or DSA based server certificate. If you are using a coupled RSA+DSA certificate pair, this will work only if actually both certificates use the same certificate chain. Else the browsers will be confused in this situation.

Example

SSLCertificateChainFile "/usr/local/apache2/conf/ssl.crt/ca.crt"

SSLCertificateFile Directive

Description:Server PEM-encoded X.509 certificate data file
Syntax:SSLCertificateFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive points to a file with certificate data in PEM format. At a minimum, the file must include an end-entity (leaf) certificate. The directive can be used multiple times (referencing different filenames) to support multiple algorithms for server authentication - typically RSA, DSA, and ECC. The number of supported algorithms depends on the OpenSSL version being used for mod_ssl: with version 1.0.0 or later, openssl list-public-key-algorithms will output a list of supported algorithms, see also the note below about limitations of OpenSSL versions prior to 1.0.2 and the ways to work around them.

The files may also include intermediate CA certificates, sorted from leaf to root. This is supported with version 2.4.8 and later, and obsoletes SSLCertificateChainFile. When running with OpenSSL 1.0.2 or later, this allows to configure the intermediate CA chain on a per-certificate basis.

Custom DH parameters and an EC curve name for ephemeral keys, can also be added to end of the first file configured using SSLCertificateFile. This is supported in version 2.4.7 or later. Such parameters can be generated using the commands openssl dhparam and openssl ecparam . The parameters can be added as-is to the end of the first certificate file. Only the first file can be used for custom parameters, as they are applied independently of the authentication algorithm type.

Finally the end-entity certificate's private key can also be added to the certificate file instead of using a separate SSLCertificateKeyFile directive. This practice is highly discouraged. If it is used, the certificate files using such an embedded key must be configured after the certificates using a separate key file. If the private key is encrypted, the pass phrase dialog is forced at startup time.

DH parameter interoperability with primes > 1024 bit

Beginning with version 2.4.7, mod_ssl makes use of standardized DH parameters with prime lengths of 2048, 3072 and 4096 bits and with additional prime lengths of 6144 and 8192 bits beginning with version 2.4.10 (from RFC 3526), and hands them out to clients based on the length of the certificate's RSA/DSA key. With Java-based clients in particular (Java 7 or earlier), this may lead to handshake failures - see this FAQ answer for working around such issues.

Default DH parameters when using multiple certificates and OpenSSL versions prior to 1.0.2

When using multiple certificates to support different authentication algorithms (like RSA, DSA, but mainly ECC) and OpenSSL prior to 1.0.2, it is recommended to either use custom DH parameters (preferably) by adding them to the first certificate file (as described above), or to order the SSLCertificateFile directives such that RSA/DSA certificates are placed after the ECC one.

This is due to a limitation in older versions of OpenSSL which don't let the Apache HTTP Server determine the currently selected certificate at handshake time (when the DH parameters must be sent to the peer) but instead always provide the last configured certificate. Consequently, the server may select default DH parameters based on the length of the wrong certificate's key (ECC keys are much smaller than RSA/DSA ones and their length is not relevant for selecting DH primes).

Since custom DH parameters always take precedence over the default ones, this issue can be avoided by creating and configuring them (as described above), thus using a custom/suitable length.

Example

SSLCertificateFile "/usr/local/apache2/conf/ssl.crt/server.crt"

SSLCertificateKeyFile Directive

Description:Server PEM-encoded private key file
Syntax:SSLCertificateKeyFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive points to the PEM-encoded private key file for the server. If the contained private key is encrypted, the pass phrase dialog is forced at startup time.

The directive can be used multiple times (referencing different filenames) to support multiple algorithms for server authentication. For each SSLCertificateKeyFile directive, there must be a matching SSLCertificateFile directive.

The private key may also be combined with the certificate in the file given by SSLCertificateFile, but this practice is highly discouraged. If it is used, the certificate files using such an embedded key must be configured after the certificates using a separate key file.

Example

SSLCertificateKeyFile "/usr/local/apache2/conf/ssl.key/server.key"

SSLCipherSuite Directive

Description:Cipher Suite available for negotiation in SSL handshake
Syntax:SSLCipherSuite [protocol] cipher-spec
Default:SSLCipherSuite DEFAULT (depends on OpenSSL version)
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

This complex directive uses a colon-separated cipher-spec string consisting of OpenSSL cipher specifications to configure the Cipher Suite the client is permitted to negotiate in the SSL handshake phase. The optional protocol specifier can configure the Cipher Suite for a specific SSL version. Possible values include "SSL" for all SSL Protocols up to and including TLSv1.2.

Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotiation with the reconfigured Cipher Suite after the HTTP request was read but before the HTTP response is sent.

If the SSL library supports TLSv1.3 (OpenSSL 1.1.1 and later), the protocol specifier "TLSv1.3" can be used to configure the cipher suites for that protocol. Since TLSv1.3 does not offer renegotiations, specifying ciphers for it in a directory context is not allowed.

For a list of TLSv1.3 cipher names, see the OpenSSL documentation.

An SSL cipher specification in cipher-spec is composed of 4 major attributes plus a few extra minor ones:

  • Key Exchange Algorithm:
    RSA, Diffie-Hellman, Elliptic Curve Diffie-Hellman, Secure Remote Password

  • Authentication Algorithm:
    RSA, Diffie-Hellman, DSS, ECDSA, or none.

  • Cipher/Encryption Algorithm:
    AES, DES, Triple-DES, RC4, RC2, IDEA, etc.

  • MAC Digest Algorithm:
    MD5, SHA or SHA1, SHA256, SHA384.

An SSL cipher can also be an export cipher. SSLv2 ciphers are no longer supported. To specify which ciphers to use, one can either specify all the Ciphers, one at a time, or use aliases to specify the preference and order for the ciphers (see Table 1). The actually available ciphers and aliases depends on the used openssl version. Newer openssl versions may include additional ciphers.

TagDescription
Key Exchange Algorithm:
kRSARSA key exchange
kDHrDiffie-Hellman key exchange with RSA key
kDHdDiffie-Hellman key exchange with DSA key
kEDHEphemeral (temp.key) Diffie-Hellman key exchange (no cert)
kSRPSecure Remote Password (SRP) key exchange
Authentication Algorithm:
aNULLNo authentication
aRSARSA authentication
aDSSDSS authentication
aDHDiffie-Hellman authentication
Cipher Encoding Algorithm:
eNULLNo encryption
NULLalias for eNULL
AESAES encryption
DESDES encryption
3DESTriple-DES encryption
RC4RC4 encryption
RC2RC2 encryption
IDEAIDEA encryption
MAC Digest Algorithm:
MD5MD5 hash function
SHA1SHA1 hash function
SHAalias for SHA1
SHA256SHA256 hash function
SHA384SHA384 hash function
Aliases:
SSLv3all SSL version 3.0 ciphers
TLSv1all TLS version 1.0 ciphers
EXPall export ciphers
EXPORT40all 40-bit export ciphers only
EXPORT56all 56-bit export ciphers only
LOWall low strength ciphers (no export, single DES)
MEDIUMall ciphers with 128 bit encryption
HIGHall ciphers using Triple-DES
RSAall ciphers using RSA key exchange
DHall ciphers using Diffie-Hellman key exchange
EDHall ciphers using Ephemeral Diffie-Hellman key exchange
ECDHElliptic Curve Diffie-Hellman key exchange
ADHall ciphers using Anonymous Diffie-Hellman key exchange
AECDHall ciphers using Anonymous Elliptic Curve Diffie-Hellman key exchange
SRPall ciphers using Secure Remote Password (SRP) key exchange
DSSall ciphers using DSS authentication
ECDSAall ciphers using ECDSA authentication
aNULLall ciphers using no authentication

Now where this becomes interesting is that these can be put together to specify the order and ciphers you wish to use. To speed this up there are also aliases ( SSLv3, TLSv1, EXP, LOW, MEDIUM, HIGH ) for certain groups of ciphers. These tags can be joined together with prefixes to form the cipher-spec. Available prefixes are:

  • none: add cipher to list

  • + : move matching ciphers to the current location in list

  • - : remove cipher from list (can be added later again)

  • ! : kill cipher from list completely (can not be added later again)

aNULL, eNULL and EXP ciphers are always disabled

Beginning with version 2.4.7, null and export-grade ciphers are always disabled, as mod_ssl unconditionally adds !aNULL:!eNULL:!EXP to any cipher string at initialization.

A simpler way to look at all of this is to use the `openssl ciphers -v` '' command which provides a nice way to successively create the correct cipher-spec string. The default cipher-spec string depends on the version of the OpenSSL libraries used. Let's suppose it is RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5 '' which means the following: Put RC4-SHA and AES128-SHA at the beginning. We do this, because these ciphers offer a good compromise between speed and security. Next, include high and medium security ciphers. Finally, remove all ciphers which do not authenticate, i.e. for SSL the Anonymous Diffie-Hellman ciphers, as well as all ciphers which use MD5 as hash algorithm, because it has been proven insufficient.

$ openssl ciphers -v 'RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5'
RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
...                     ...               ...     ...           ...
SEED-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=SEED(128) Mac=SHA1
PSK-RC4-SHA             SSLv3 Kx=PSK      Au=PSK  Enc=RC4(128)  Mac=SHA1
KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1

The complete list of particular RSA & DH ciphers for SSL is given in Table 2.

Example

SSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW
Cipher-TagProtocolKey Ex.Auth.Enc.MACType
RSA Ciphers:
DES-CBC3-SHASSLv3RSARSA3DES(168)SHA1
IDEA-CBC-SHASSLv3RSARSAIDEA(128)SHA1
RC4-SHASSLv3RSARSARC4(128)SHA1
RC4-MD5SSLv3RSARSARC4(128)MD5
DES-CBC-SHASSLv3RSARSADES(56)SHA1
EXP-DES-CBC-SHASSLv3RSA(512)RSADES(40)SHA1export
EXP-RC2-CBC-MD5SSLv3RSA(512)RSARC2(40)MD5export
EXP-RC4-MD5SSLv3RSA(512)RSARC4(40)MD5export
NULL-SHASSLv3RSARSANoneSHA1
NULL-MD5SSLv3RSARSANoneMD5
Diffie-Hellman Ciphers:
ADH-DES-CBC3-SHASSLv3DHNone3DES(168)SHA1
ADH-DES-CBC-SHASSLv3DHNoneDES(56)SHA1
ADH-RC4-MD5SSLv3DHNoneRC4(128)MD5
EDH-RSA-DES-CBC3-SHASSLv3DHRSA3DES(168)SHA1
EDH-DSS-DES-CBC3-SHASSLv3DHDSS3DES(168)SHA1
EDH-RSA-DES-CBC-SHASSLv3DHRSADES(56)SHA1
EDH-DSS-DES-CBC-SHASSLv3DHDSSDES(56)SHA1
EXP-EDH-RSA-DES-CBC-SHASSLv3DH(512)RSADES(40)SHA1export
EXP-EDH-DSS-DES-CBC-SHASSLv3DH(512)DSSDES(40)SHA1export
EXP-ADH-DES-CBC-SHASSLv3DH(512)NoneDES(40)SHA1export
EXP-ADH-RC4-MD5SSLv3DH(512)NoneRC4(40)MD5export

SSLCompression Directive

Description:Enable compression on the SSL level
Syntax:SSLCompression on\|off
Default:SSLCompression off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.3 and later, if using OpenSSL 0.9.8 or later; virtual host scope available if using OpenSSL 1.0.0 or later. The default used to be on in version 2.4.3.

This directive allows to enable compression on the SSL level.

Enabling compression causes security issues in most setups (the so called CRIME attack).

SSLCryptoDevice Directive

Description:Enable use of a cryptographic hardware accelerator
Syntax:SSLCryptoDevice engine
Default:SSLCryptoDevice builtin
Context:server config
Status:Extension
Module:mod_ssl

This directive enables use of a cryptographic hardware accelerator board to offload some of the SSL processing overhead. This directive can only be used if the SSL toolkit is built with "engine" support; OpenSSL 0.9.7 and later releases have "engine" support by default, the separate "-engine" releases of OpenSSL 0.9.6 must be used.

To discover which engine names are supported, run the command " openssl engine ".

Example

# For a Broadcom accelerator:
SSLCryptoDevice ubsec

SSLEngine Directive

Description:SSL Engine Operation Switch
Syntax:SSLEngine on\|off\|optional
Default:SSLEngine off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive toggles the usage of the SSL/TLS Protocol Engine. This is should be used inside a <VirtualHost> section to enable SSL/TLS for a that virtual host. By default the SSL/TLS Protocol Engine is disabled for both the main server and all configured virtual hosts.

Example

<VirtualHost _default_:443>
SSLEngine on
#...
</VirtualHost>

In Apache 2.1 and later, SSLEngine can be set to optional . This enables support for RFC 2817, Upgrading to TLS Within HTTP/1.1. At this time no web browsers support RFC 2817.

SSLFIPS Directive

Description:SSL FIPS mode Switch
Syntax:SSLFIPS on\|off
Default:SSLFIPS off
Context:server config
Status:Extension
Module:mod_ssl

This directive toggles the usage of the SSL library FIPS_mode flag. It must be set in the global server context and cannot be configured with conflicting settings (SSLFIPS on followed by SSLFIPS off or similar). The mode applies to all SSL library operations.

If httpd was compiled against an SSL library which did not support the FIPS_mode flag, SSLFIPS on will fail. Refer to the FIPS 140-2 Security Policy document of the SSL provider library for specific requirements to use mod_ssl in a FIPS 140-2 approved mode of operation; note that mod_ssl itself is not validated, but may be described as using FIPS 140-2 validated cryptographic module, when all components are assembled and operated under the guidelines imposed by the applicable Security Policy.

SSLHonorCipherOrder Directive

Description:Option to prefer the server's cipher preference order
Syntax:SSLHonorCipherOrder on\|off
Default:SSLHonorCipherOrder off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

When choosing a cipher during an SSLv3 or TLSv1 handshake, normally the client's preference is used. If this directive is enabled, the server's preference will be used instead.

Example

SSLHonorCipherOrder on

SSLInsecureRenegotiation Directive

Description:Option to enable support for insecure renegotiation
Syntax:SSLInsecureRenegotiation on\|off
Default:SSLInsecureRenegotiation off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.2.15 and later, if using OpenSSL 0.9.8m or later

As originally specified, all versions of the SSL and TLS protocols (up to and including TLS/1.2) were vulnerable to a Man-in-the-Middle attack (CVE-2009-3555) during a renegotiation. This vulnerability allowed an attacker to "prefix" a chosen plaintext to the HTTP request as seen by the web server. A protocol extension was developed which fixed this vulnerability if supported by both client and server.

If mod_ssl is linked against OpenSSL version 0.9.8m or later, by default renegotiation is only supported with clients supporting the new protocol extension. If this directive is enabled, renegotiation will be allowed with old (unpatched) clients, albeit insecurely.

Security warning

If this directive is enabled, SSL connections will be vulnerable to the Man-in-the-Middle prefix attack as described in CVE-2009-3555.

Example

SSLInsecureRenegotiation on

The SSL_SECURE_RENEG environment variable can be used from an SSI or CGI script to determine whether secure renegotiation is supported for a given SSL connection.

SSLOCSPDefaultResponder Directive

Description:Set the default responder URI for OCSP validation
Syntax:SSLOCSPDefaultResponder uri
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the default OCSP responder to use. If SSLOCSPOverrideResponder is not enabled, the URI given will be used only if no responder URI is specified in the certificate being verified.

SSLOCSPEnable Directive

Description:Enable OCSP validation of the client certificate chain
Syntax:SSLOCSPEnable on\|leaf\|off
Default:SSLOCSPEnable off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Mode leaf available in httpd 2.4.34 and later

This option enables OCSP validation of the client certificate chain. If this option is enabled, certificates in the client's certificate chain will be validated against an OCSP responder after normal verification (including CRL checks) have taken place. In mode 'leaf', only the client certificate itself will be validated.

The OCSP responder used is either extracted from the certificate itself, or derived by configuration; see the SSLOCSPDefaultResponder and SSLOCSPOverrideResponder directives.

Example

SSLVerifyClient on
SSLOCSPEnable on
SSLOCSPDefaultResponder "http://responder.example.com:8888/responder"
SSLOCSPOverrideResponder on

SSLOCSPNoverify Directive

Description:skip the OCSP responder certificates verification
Syntax:SSLOCSPNoverify On/Off
Default:SSLOCSPNoverify Off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.26 and later, if using OpenSSL 0.9.7 or later

Skip the OCSP responder certificates verification, mostly useful when testing an OCSP server.

SSLOCSPOverrideResponder Directive

Description:Force use of the default responder URI for OCSP validation
Syntax:SSLOCSPOverrideResponder on\|off
Default:SSLOCSPOverrideResponder off
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option forces the configured default OCSP responder to be used during OCSP certificate validation, regardless of whether the certificate being validated references an OCSP responder.

SSLOCSPProxyURL Directive

Description:Proxy URL to use for OCSP requests
Syntax:SSLOCSPProxyURL url
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.19 and later

This option allows to set the URL of a HTTP proxy that should be used for all queries to OCSP responders.

SSLOCSPResponderCertificateFile Directive

Description:Set of trusted PEM encoded OCSP responder certificates
Syntax:SSLOCSPResponderCertificateFile file
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.26 and later, if using OpenSSL 0.9.7 or later

This supplies a list of trusted OCSP responder certificates to be used during OCSP responder certificate validation. The supplied certificates are implicitly trusted without any further validation. This is typically used where the OCSP responder certificate is self signed or omitted from the OCSP response.

SSLOCSPResponderTimeout Directive

Description:Timeout for OCSP queries
Syntax:SSLOCSPResponderTimeout seconds
Default:SSLOCSPResponderTimeout 10
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the timeout for queries to OCSP responders, when SSLOCSPEnable is turned on.

SSLOCSPResponseMaxAge Directive

Description:Maximum allowable age for OCSP responses
Syntax:SSLOCSPResponseMaxAge seconds
Default:SSLOCSPResponseMaxAge -1
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the maximum allowable age ("freshness") for OCSP responses. The default value ( -1 ) does not enforce a maximum age, which means that OCSP responses are considered valid as long as their nextUpdate field is in the future.

SSLOCSPResponseTimeSkew Directive

Description:Maximum allowable time skew for OCSP response validation
Syntax:SSLOCSPResponseTimeSkew seconds
Default:SSLOCSPResponseTimeSkew 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This option sets the maximum allowable time skew for OCSP responses (when checking their thisUpdate and nextUpdate fields).

SSLOCSPUseRequestNonce Directive

Description:Use a nonce within OCSP queries
Syntax:SSLOCSPUseRequestNonce on\|off
Default:SSLOCSPUseRequestNonce on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.10 and later

This option determines whether queries to OCSP responders should contain a nonce or not. By default, a query nonce is always used and checked against the response's one. When the responder does not use nonces (e.g. Microsoft OCSP Responder), this option should be turned off .

SSLOpenSSLConfCmd Directive

Description:Configure OpenSSL parameters through its SSL_CONF API
Syntax:SSLOpenSSLConfCmd command-name command-value
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.8 and later, if using OpenSSL 1.0.2 or later

This directive exposes OpenSSL's SSL_CONF API to mod_ssl, allowing a flexible configuration of OpenSSL parameters without the need of implementing additional mod_ssl directives when new features are added to OpenSSL.

The set of available SSLOpenSSLConfCmd commands depends on the OpenSSL version being used for mod_ssl (at least version 1.0.2 is required). For a list of supported command names, see the section Supported configuration file commands in the SSL_CONF_cmd(3) manual page for OpenSSL.

Some of the SSLOpenSSLConfCmd commands can be used as an alternative to existing directives (such as SSLCipherSuite or SSLProtocol), though it should be noted that the syntax / allowable values for the parameters may sometimes differ.

Examples

SSLOpenSSLConfCmd Options -SessionTicket,ServerPreference
SSLOpenSSLConfCmd ECDHParameters brainpoolP256r1
SSLOpenSSLConfCmd ServerInfoFile "/usr/local/apache2/conf/server-info.pem"
SSLOpenSSLConfCmd Protocol "-ALL, TLSv1.2"
SSLOpenSSLConfCmd SignatureAlgorithms RSA+SHA384:ECDSA+SHA256

SSLOptions Directive

Description:Configure various SSL engine run-time options
Syntax:SSLOptions [+\|-]option ...
Context:server config, virtual host, directory, .htaccess
Override:Options
Status:Extension
Module:mod_ssl

This directive can be used to control various run-time options on a per-directory basis. Normally, if multiple SSLOptions could apply to a directory, then the most specific one is taken completely; the options are not merged. However if all the options on the SSLOptions directive are preceded by a plus ( + ) or minus ( - ) symbol, the options are merged. Any options preceded by a + are added to the options currently in force, and any options preceded by a - are removed from the options currently in force.

The available options are:

  • StdEnvVars
    When this option is enabled, the standard set of SSL related CGI/SSI environment variables are created. This per default is disabled for performance reasons, because the information extraction step is a rather expensive operation. So one usually enables this option for CGI and SSI requests only.

  • ExportCertData
    When this option is enabled, additional CGI/SSI environment variables are created: SSL_SERVER_CERT , SSL_CLIENT_CERT and SSL_CLIENT_CERT_CHAIN_ n (with n = 0,1,2,..). These contain the PEM-encoded X.509 Certificates of server and client for the current HTTPS connection and can be used by CGI scripts for deeper Certificate checking. Additionally all other certificates of the client certificate chain are provided, too. This bloats up the environment a little bit which is why you have to use this option to enable it on demand.

  • FakeBasicAuth
    When this option is enabled, the Subject Distinguished Name (DN) of the Client X509 Certificate is translated into a HTTP Basic Authorization username. This means that the standard Apache authentication methods can be used for access control. The user name is just the Subject of the Client's X509 Certificate (can be determined by running OpenSSL's openssl x509 command: openssl x509 -noout -subject -in certificate .crt ). Note that no password is obtained from the user. Every entry in the user file needs this password: `xxj31ZMTZzkVA` '', which is the DES-encrypted version of the word ` `password` ''. Those who live under MD5-based encryption (for instance under FreeBSD or BSD/OS, etc.) should use the following MD5 hash of the same word: $1$OXLyS...$Owx8s2/m9/gfkcRVXzgoE/ ''.

Note that the AuthBasicFake directive within mod_auth_basic can be used as a more general mechanism for faking basic authentication, giving control over the structure of both the username and password.

  • StrictRequire
    This forces forbidden access when SSLRequireSSL or SSLRequire successfully decided that access should be forbidden. Usually the default is that in the case where a `Satisfy any` '' directive is used, and other access restrictions are passed, denial of access due to `SSLRequireSSL` or `SSLRequire` is overridden (because that's how the Apache `Satisfy` mechanism should work.) But for strict access restriction you can use `SSLRequireSSL` and/or `SSLRequire` in combination with an SSLOptions +StrictRequire ''. Then an additional `` Satisfy Any '' has no chance once mod_ssl has decided to deny access.

  • OptRenegotiate
    This enables optimized SSL connection renegotiation handling when SSL directives are used in per-directory context. By default a strict scheme is enabled where every per-directory reconfiguration of SSL parameters causes a full SSL renegotiation handshake. When this option is used mod_ssl tries to avoid unnecessary handshakes by doing more granular (but still safe) parameter checks. Nevertheless these granular checks sometimes may not be what the user expects, so enable this on a per-directory basis only, please.

  • LegacyDNStringFormat
    This option influences how values of the SSL_{CLIENT,SERVER}_{I,S}_DN variables are formatted. Since version 2.3.11, Apache HTTPD uses a RFC 2253 compatible format by default. This uses commas as delimiters between the attributes, allows the use of non-ASCII characters (which are converted to UTF8), escapes various special characters with backslashes, and sorts the attributes with the "C" attribute last.

If LegacyDNStringFormat is set, the old format will be used which sorts the "C" attribute first, uses slashes as separators, and does not handle non-ASCII and special characters in any consistent way.

Example

SSLOptions +FakeBasicAuth -StrictRequire
<Files ~ "\.(cgi|shtml)$">
    SSLOptions +StdEnvVars -ExportCertData
</Files>

SSLPassPhraseDialog Directive

Description:Type of pass phrase dialog for encrypted private keys
Syntax:SSLPassPhraseDialog type
Default:SSLPassPhraseDialog builtin
Context:server config
Status:Extension
Module:mod_ssl

When Apache starts up it has to read the various Certificate (see SSLCertificateFile) and Private Key (see SSLCertificateKeyFile) files of the SSL-enabled virtual servers. Because for security reasons the Private Key files are usually encrypted, mod_ssl needs to query the administrator for a Pass Phrase in order to decrypt those files. This query can be done in two ways which can be configured by type:

  • builtin
    This is the default where an interactive terminal dialog occurs at startup time just before Apache detaches from the terminal. Here the administrator has to manually enter the Pass Phrase for each encrypted Private Key file. Because a lot of SSL-enabled virtual hosts can be configured, the following reuse-scheme is used to minimize the dialog: When a Private Key file is encrypted, all known Pass Phrases (at the beginning there are none, of course) are tried. If one of those known Pass Phrases succeeds no dialog pops up for this particular Private Key file. If none succeeded, another Pass Phrase is queried on the terminal and remembered for the next round (where it perhaps can be reused).

This scheme allows mod_ssl to be maximally flexible (because for N encrypted Private Key files you can use N different Pass Phrases - but then you have to enter all of them, of course) while minimizing the terminal dialog (i.e. when you use a single Pass Phrase for all N Private Key files this Pass Phrase is queried only once).

  • |/path/to/program [args...]
    This mode allows an external program to be used which acts as a pipe to a particular input device; the program is sent the standard prompt text used for the builtin mode on stdin , and is expected to write password strings on stdout . If several passwords are needed (or an incorrect password is entered), additional prompt text will be written subsequent to the first password being returned, and more passwords must then be written back.

  • exec:/path/to/program
    Here an external program is configured which is called at startup for each encrypted Private Key file. It is called with two arguments (the first is of the form `servername:portnumber` '', the second is either RSA '', `DSA` '', ECC '' or an integer index starting at 3 if more than three keys are configured), which indicate for which server and algorithm it has to print the corresponding Pass Phrase to stdout . In versions 2.4.8 (unreleased) and 2.4.9, it is called with one argument, a string of the form `` servername:portnumber:index '' (with index being a zero-based integer number), which indicate the server, TCP port and certificate number. The intent is that this external program first runs security checks to make sure that the system is not compromised by an attacker, and only when these checks were passed successfully it provides the Pass Phrase.

Both these security checks, and the way the Pass Phrase is determined, can be as complex as you like. Mod_ssl just defines the interface: an executable program which provides the Pass Phrase on stdout . Nothing more or less! So, if you're really paranoid about security, here is your interface. Anything else has to be left as an exercise to the administrator, because local security requirements are so different.

The reuse-algorithm above is used here, too. In other words: The external program is called only once per unique Pass Phrase.

Example

SSLPassPhraseDialog "exec:/usr/local/apache/sbin/pp-filter"

SSLProtocol Directive

Description:Configure usable SSL/TLS protocol versions
Syntax:SSLProtocol [+\|-]protocol ...
Default:SSLProtocol all -SSLv3 (up to 2.4.16: all)
Context:server config, virtual host
Status:Extension
Module:mod_ssl

This directive can be used to control which versions of the SSL/TLS protocol will be accepted in new connections.

The available (case-insensitive) protocols are:

  • SSLv3
    This is the Secure Sockets Layer (SSL) protocol, version 3.0, from the Netscape Corporation. It is the successor to SSLv2 and the predecessor to TLSv1, but is deprecated in RFC 7568.

  • TLSv1
    This is the Transport Layer Security (TLS) protocol, version 1.0. It is the successor to SSLv3 and is defined in RFC 2246. It is supported by nearly every client.

  • TLSv1.1 (when using OpenSSL 1.0.1 and later)
    A revision of the TLS 1.0 protocol, as defined in RFC 4346.

  • TLSv1.2 (when using OpenSSL 1.0.1 and later)
    A revision of the TLS 1.1 protocol, as defined in RFC 5246.

  • TLSv1.3 (when using OpenSSL 1.1.1 and later)
    A new version of the TLS protocol, as defined in RFC 8446.

  • all
    This is a shortcut for `+SSLv3 +TLSv1` '' or - when using OpenSSL 1.0.1 and later - +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2 '', respectively (except for OpenSSL versions compiled with the ``no-ssl3'' configuration option, where all does not include +SSLv3 ).

Example

SSLProtocol TLSv1

SSLProxyCACertificateFile Directive

Description:File of concatenated PEM-encoded CA Certificates for Remote Server Auth
Syntax:SSLProxyCACertificateFile file-path
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the all-in-one file where you can assemble the Certificates of Certification Authorities (CA) whose remote servers you deal with. These are used for Remote Server Authentication. Such a file is simply the concatenation of the various PEM-encoded Certificate files, in order of preference. This can be used alternatively and/or additionally to SSLProxyCACertificatePath.

Example

SSLProxyCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-remote-server.crt"

SSLProxyCACertificatePath Directive

Description:Directory of PEM-encoded CA Certificates for Remote Server Auth
Syntax:SSLProxyCACertificatePath directory-path
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the directory where you keep the Certificates of Certification Authorities (CAs) whose remote servers you deal with. These are used to verify the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through hash filenames. So usually you can't just place the Certificate files there: you also have to create symbolic links named hash-value .N . And you should always make sure this directory contains the appropriate symbolic links.

Example

SSLProxyCACertificatePath "/usr/local/apache2/conf/ssl.crt/"

SSLProxyCARevocationCheck Directive

Description:Enable CRL-based revocation checking for Remote Server Auth
Syntax:SSLProxyCARevocationCheck chain\|leaf\|none
Default:SSLProxyCARevocationCheck none
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

Enables certificate revocation list (CRL) checking for the remote servers you deal with. At least one of SSLProxyCARevocationFile or SSLProxyCARevocationPath must be configured. When set to chain (recommended setting), CRL checks are applied to all certificates in the chain, while setting it to leaf limits the checks to the end-entity cert.

When set to chain or leaf, CRLs must be available for successful validation

Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when no CRL(s) were found in any of the locations configured with SSLProxyCARevocationFile or SSLProxyCARevocationPath. With the introduction of this directive, the behavior has been changed: when checking is enabled, CRLs must be present for the validation to succeed - otherwise it will fail with an "unable to get certificate CRL" error.

Example

SSLProxyCARevocationCheck chain

SSLProxyCARevocationFile Directive

Description:File of concatenated PEM-encoded CA CRLs for Remote Server Auth
Syntax:SSLProxyCARevocationFile file-path
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the all-in-one file where you can assemble the Certificate Revocation Lists (CRL) of Certification Authorities (CA) whose remote servers you deal with. These are used for Remote Server Authentication. Such a file is simply the concatenation of the various PEM-encoded CRL files, in order of preference. This can be used alternatively and/or additionally to SSLProxyCARevocationPath.

Example

SSLProxyCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-remote-server.crl"

SSLProxyCARevocationPath Directive

Description:Directory of PEM-encoded CA CRLs for Remote Server Auth
Syntax:SSLProxyCARevocationPath directory-path
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the directory where you keep the Certificate Revocation Lists (CRL) of Certification Authorities (CAs) whose remote servers you deal with. These are used to revoke the remote server certificate on Remote Server Authentication.

The files in this directory have to be PEM-encoded and are accessed through hash filenames. So usually you have not only to place the CRL files there. Additionally you have to create symbolic links named hash-value .rN . And you should always make sure this directory contains the appropriate symbolic links.

Example

SSLProxyCARevocationPath "/usr/local/apache2/conf/ssl.crl/"

SSLProxyCheckPeerCN Directive

Description:Whether to check the remote server certificate's CN field
Syntax:SSLProxyCheckPeerCN on\|off
Default:SSLProxyCheckPeerCN on
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets whether the remote server certificate's CN field is compared against the hostname of the request URL. If both are not equal a 502 status code (Bad Gateway) is sent. SSLProxyCheckPeerCN is superseded by SSLProxyCheckPeerName in release 2.4.5 and later.

In all releases 2.4.5 through 2.4.20, setting SSLProxyCheckPeerName off was sufficient to enable this behavior (as the SSLProxyCheckPeerCN default was on .) In these releases, both directives must be set to off to completely avoid remote server certificate name validation. Many users reported this to be very confusing.

As of release 2.4.21, all configurations which enable either one of the SSLProxyCheckPeerName or SSLProxyCheckPeerCN options will use the new SSLProxyCheckPeerName behavior, and all configurations which disable either one of the SSLProxyCheckPeerName or SSLProxyCheckPeerCN options will suppress all remote server certificate name validation. Only the following configuration will trigger the legacy certificate CN comparison in 2.4.21 and later releases;

Example

SSLProxyCheckPeerCN on
SSLProxyCheckPeerName off

SSLProxyCheckPeerExpire Directive

Description:Whether to check if remote server certificate is expired
Syntax:SSLProxyCheckPeerExpire on\|off
Default:SSLProxyCheckPeerExpire on
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets whether it is checked if the remote server certificate is expired or not. If the check fails a 502 status code (Bad Gateway) is sent.

Example

SSLProxyCheckPeerExpire on

SSLProxyCheckPeerName Directive

Description:Configure host name checking for remote server certificates
Syntax:SSLProxyCheckPeerName on\|off
Default:SSLProxyCheckPeerName on
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:Apache HTTP Server 2.4.5 and later
The proxy section context is allowed in httpd 2.4.30 and later

This directive configures host name checking for server certificates when mod_ssl is acting as an SSL client. The check will succeed if the host name from the request URI matches one of the CN attribute(s) of the certificate's subject, or matches the subjectAltName extension. If the check fails, the SSL request is aborted and a 502 status code (Bad Gateway) is returned.

Wildcard matching is supported for specific cases: an subjectAltName entry of type dNSName, or CN attributes starting with *. will match with any host name of the same number of name elements and the same suffix. E.g. *.example.org will match foo.example.org , but will not match foo.bar.example.org , because the number of elements in the respective host names differs.

This feature was introduced in 2.4.5 and superseded the behavior of the SSLProxyCheckPeerCN directive, which only tested the exact value in the first CN attribute against the host name. However, many users were confused by the behavior of using these directives individually, so the mutual behavior of SSLProxyCheckPeerName and SSLProxyCheckPeerCN directives were improved in release 2.4.21. See the SSLProxyCheckPeerCN directive description for the original behavior and details of these improvements.

SSLProxyCipherSuite Directive

Description:Cipher Suite available for negotiation in SSL proxy handshake
Syntax:SSLProxyCipherSuite [protocol] cipher-spec
Default:SSLProxyCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+EXP
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

Equivalent to SSLCipherSuite, but for the proxy connection. Please refer to SSLCipherSuite for additional information.

SSLProxyEngine Directive

Description:SSL Proxy Engine Operation Switch
Syntax:SSLProxyEngine on\|off
Default:SSLProxyEngine off
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive toggles the usage of the SSL/TLS Protocol Engine for proxy. This is usually used inside a <VirtualHost> section to enable SSL/TLS for proxy usage in a particular virtual host. By default the SSL/TLS Protocol Engine is disabled for proxy both for the main server and all configured virtual hosts.

Note that the SSLProxyEngine directive should not, in general, be included in a virtual host that will be acting as a forward proxy (using <Proxy> or ProxyRequests directives). SSLProxyEngine is not required to enable a forward proxy server to proxy SSL/TLS requests.

Example

<VirtualHost _default_:443>
    SSLProxyEngine on
    #...
</VirtualHost>

SSLProxyMachineCertificateChainFile Directive

Description:File of concatenated PEM-encoded CA certificates to be used by the proxy for choosing a certificate
Syntax:SSLProxyMachineCertificateChainFile filename
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the all-in-one file where you keep the certificate chain for all of the client certs in use. This directive will be needed if the remote server presents a list of CA certificates that are not direct signers of one of the configured client certificates.

This referenced file is simply the concatenation of the various PEM-encoded certificate files. Upon startup, each client certificate configured will be examined and a chain of trust will be constructed.

Security warning

If this directive is enabled, all of the certificates in the file will be trusted as if they were also in SSLProxyCACertificateFile.

Example

SSLProxyMachineCertificateChainFile "/usr/local/apache2/conf/ssl.crt/proxyCA.pem"

SSLProxyMachineCertificateFile Directive

Description:File of concatenated PEM-encoded client certificates and keys to be used by the proxy
Syntax:SSLProxyMachineCertificateFile filename
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the all-in-one file where you keep the certificates and keys used for authentication of the proxy server to remote servers.

This referenced file is simply the concatenation of the various PEM-encoded certificate files, in order of preference. Use this directive alternatively or additionally to SSLProxyMachineCertificatePath .

Currently there is no support for encrypted private keys

Example

SSLProxyMachineCertificateFile "/usr/local/apache2/conf/ssl.crt/proxy.pem"

SSLProxyMachineCertificatePath Directive

Description:Directory of PEM-encoded client certificates and keys to be used by the proxy
Syntax:SSLProxyMachineCertificatePath directory
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets the directory where you keep the certificates and keys used for authentication of the proxy server to remote servers.

The files in this directory must be PEM-encoded and are accessed through hash filenames. Additionally, you must create symbolic links named hash-value.N . And you should always make sure this directory contains the appropriate symbolic links.

Currently there is no support for encrypted private keys

Example

SSLProxyMachineCertificatePath "/usr/local/apache2/conf/proxy.crt/"

SSLProxyProtocol Directive

Description:Configure usable SSL protocol flavors for proxy usage
Syntax:SSLProxyProtocol [+\|-]protocol ...
Default:SSLProxyProtocol all -SSLv3 (up to 2.4.16: all)
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive can be used to control the SSL protocol flavors mod_ssl should use when establishing its server environment for proxy . It will only connect to servers using one of the provided protocols.

Please refer to SSLProtocol for additional information.

SSLProxyVerify Directive

Description:Type of remote server Certificate verification
Syntax:SSLProxyVerify level
Default:SSLProxyVerify none
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

When a proxy is configured to forward requests to a remote SSL server, this directive can be used to configure certificate verification of the remote server.

The following levels are available for level:

  • none : no remote server Certificate is required at all

  • optional : the remote server may present a valid Certificate

  • require : the remote server has to present a valid Certificate

  • optional_no_ca : the remote server may present a valid Certificate
    but it need not to be (successfully) verifiable.

In practice only levels none and require are really interesting, because level optional doesn't work with all servers and level optional_no_ca is actually against the idea of authentication (but can be used to establish SSL test pages, etc.)

Example

SSLProxyVerify require

SSLProxyVerifyDepth Directive

Description:Maximum depth of CA Certificates in Remote Server Certificate verification
Syntax:SSLProxyVerifyDepth number
Default:SSLProxyVerifyDepth 1
Context:server config, virtual host, proxy section
Status:Extension
Module:mod_ssl
Compatibility:The proxy section context is allowed in httpd 2.4.30 and later

This directive sets how deeply mod_ssl should verify before deciding that the remote server does not have a valid certificate.

The depth actually is the maximum number of intermediate certificate issuers, i.e. the number of CA certificates which are max allowed to be followed while verifying the remote server certificate. A depth of 0 means that self-signed remote server certificates are accepted only, the default depth of 1 means the remote server certificate can be self-signed or has to be signed by a CA which is directly known to the server (i.e. the CA's certificate is under SSLProxyCACertificatePath), etc.

Example

SSLProxyVerifyDepth 10

SSLRandomSeed Directive

Description:Pseudo Random Number Generator (PRNG) seeding source
Syntax:SSLRandomSeed context source [bytes]
Context:server config
Status:Extension
Module:mod_ssl

This configures one or more sources for seeding the Pseudo Random Number Generator (PRNG) in OpenSSL at startup time (context is startup ) and/or just before a new SSL connection is established (context is connect ). This directive can only be used in the global server context because the PRNG is a global facility.

The following source variants are available:

  • builtin
    This is the always available builtin seeding source. Its usage consumes minimum CPU cycles under runtime and hence can be always used without drawbacks. The source used for seeding the PRNG contains of the current time, the current process id and a randomly chosen 128 bytes extract of the stack. The drawback is that this is not really a strong source and at startup time (where the scoreboard is still not available) this source just produces a few bytes of entropy. So you should always, at least for the startup, use an additional seeding source.

  • file:/path/to/source
    This variant uses an external file /path/to/source as the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of the file form the entropy (and bytes is given to /path/to/source as the first argument). When bytes is not specified the whole file forms the entropy (and 0 is given to /path/to/source as the first argument). Use this especially at startup time, for instance with an available /dev/random and/or /dev/urandom devices (which usually exist on modern Unix derivatives like FreeBSD and Linux).

But be careful: Usually /dev/random provides only as much entropy data as it actually has, i.e. when you request 512 bytes of entropy, but the device currently has only 100 bytes available two things can happen: On some platforms you receive only the 100 bytes while on other platforms the read blocks until enough bytes are available (which can take a long time). Here using an existing /dev/urandom is better, because it never blocks and actually gives the amount of requested data. The drawback is just that the quality of the received data may not be the best.

  • exec:/path/to/program
    This variant uses an external executable /path/to/program as the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of its stdout contents form the entropy. When bytes is not specified, the entirety of the data produced on stdout form the entropy. Use this only at startup time when you need a very strong seeding with the help of an external program (for instance as in the example above with the truerand utility you can find in the mod_ssl distribution which is based on the AT&T truerand library). Using this in the connection context slows down the server too dramatically, of course. So usually you should avoid using external programs in that context.

  • egd:/path/to/egd-socket (Unix only)
    This variant uses the Unix domain socket of the external Entropy Gathering Daemon (EGD) (see http://www.lothar.com/tech /crypto/) to seed the PRNG. Use this if no random device exists on your platform.

Example

SSLRandomSeed startup builtin
SSLRandomSeed startup "file:/dev/random"
SSLRandomSeed startup "file:/dev/urandom" 1024
SSLRandomSeed startup "exec:/usr/local/bin/truerand" 16
SSLRandomSeed connect builtin
SSLRandomSeed connect "file:/dev/random"
SSLRandomSeed connect "file:/dev/urandom" 1024

SSLRenegBufferSize Directive

Description:Set the size for the SSL renegotiation buffer
Syntax:SSLRenegBufferSize bytes
Default:SSLRenegBufferSize 131072
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

If an SSL renegotiation is required in per-location context, for example, any use of SSLVerifyClient in a Directory or Location block, then mod_ssl must buffer any HTTP request body into memory until the new SSL handshake can be performed. This directive can be used to set the amount of memory that will be used for this buffer.

Note that in many configurations, the client sending the request body will be untrusted so a denial of service attack by consumption of memory must be considered when changing this configuration setting.

Example

SSLRenegBufferSize 262144

SSLRequire Directive

Description:Allow access only when an arbitrarily complex boolean expression is true
Syntax:SSLRequire expression
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

SSLRequire is deprecated

SSLRequire is deprecated and should in general be replaced by Require expr. The so called ap_expr syntax of Require expr is a superset of the syntax of SSLRequire , with the following exception:

In SSLRequire , the comparison operators < , <= , ... are completely equivalent to the operators lt , le , ... and work in a somewhat peculiar way that first compares the length of two strings and then the lexical order. On the other hand, ap_expr has two sets of comparison operators: The operators < , <= , ... do lexical string comparison, while the operators -lt , -le , ... do integer comparison. For the latter, there are also aliases without the leading dashes: lt , le , ...

This directive specifies a general access requirement which has to be fulfilled in order to allow access. It is a very powerful directive because the requirement specification is an arbitrarily complex boolean expression containing any number of access checks.

The expression must match the following syntax (given as a BNF grammar notation):

expr     ::= "true" | "false"
           | "!" expr
           | expr "&&" expr
           | expr "||" expr
           | "(" expr ")"
           | comp

comp     ::= word "==" word | word "eq" word
           | word "!=" word | word "ne" word
           | word "<"  word | word "lt" word
           | word "<=" word | word "le" word
           | word ">"  word | word "gt" word
           | word ">=" word | word "ge" word
           | word "in" "{" wordlist "}"
           | word "in" "PeerExtList(" word ")"
           | word "=~" regex
           | word "!~" regex

wordlist ::= word
           | wordlist "," word

word     ::= digit
           | cstring
           | variable
           | function

digit    ::= [0-9]+
cstring  ::= "..."
variable ::= "%{" varname "}"
function ::= funcname "(" funcargs ")"

For varname any of the variables described in Environment Variables can be used. For funcname the available functions are listed in the ap_expr documentation.

The expression is parsed into an internal machine representation when the configuration is loaded, and then evaluated during request processing. In .htaccess context, the expression is both parsed and executed each time the .htaccess file is encountered during request processing.

Example

SSLRequire (    %{SSL_CIPHER} !~ m/^(EXP|NULL)-/                   \
            and %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd."          \
            and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"}    \
            and %{TIME_WDAY} -ge 1 and %{TIME_WDAY} -le 5          \
            and %{TIME_HOUR} -ge 8 and %{TIME_HOUR} -le 20       ) \
           or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/

The PeerExtList(object-ID) function expects to find zero or more instances of the X.509 certificate extension identified by the given object ID (OID) in the client certificate. The expression evaluates to true if the left-hand side string matches exactly against the value of an extension identified with this OID. (If multiple extensions with the same OID are present, at least one extension must match).

Example

SSLRequire "foobar" in PeerExtList("1.2.3.4.5.6")

Notes on the PeerExtList function

  • The object ID can be specified either as a descriptive name recognized by the SSL library, such as "nsComment" , or as a numeric OID, such as "1.2.3.4.5.6" .

  • Expressions with types known to the SSL library are rendered to a string before comparison. For an extension with a type not recognized by the SSL library, mod_ssl will parse the value if it is one of the primitive ASN.1 types UTF8String, IA5String, VisibleString, or BMPString. For an extension of one of these types, the string value will be converted to UTF-8 if necessary, then compared against the left-hand-side expression.

See also

SSLRequireSSL Directive

Description:Deny access when SSL is not used for the HTTP request
Syntax:SSLRequireSSL
Context:directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for the current connection. This is very handy inside the SSL-enabled virtual host or directories for defending against configuration errors that expose stuff that should be protected. When this directive is present all requests are denied which are not using SSL.

Example

SSLRequireSSL

SSLSessionCache Directive

Description:Type of the global/inter-process SSL Session Cache
Syntax:SSLSessionCache type
Default:SSLSessionCache none
Context:server config
Status:Extension
Module:mod_ssl

This configures the storage type of the global/inter-process SSL Session Cache. This cache is an optional facility which speeds up parallel request processing. For requests to the same server process (via HTTP keep-alive), OpenSSL already caches the SSL session information locally. But because modern clients request inlined images and other data via parallel requests (usually up to four parallel requests are common) those requests are served by different pre-forked server processes. Here an inter-process cache helps to avoid unnecessary session handshakes.

The following five storage types are currently supported:

  • none
    This disables the global/inter-process Session Cache. This will incur a noticeable speed penalty and may cause problems if using certain browsers, particularly if client certificates are enabled. This setting is not recommended.

  • nonenotnull
    This disables any global/inter-process Session Cache. However it does force OpenSSL to send a non-null session ID to accommodate buggy clients that require one.

  • dbm:/path/to/datafile
    This makes use of a DBM hashfile on the local disk to synchronize the local OpenSSL memory caches of the server processes. This session cache may suffer reliability issues under high load. To use this, ensure that mod_socache_dbm is loaded.

  • shmcb:/path/to/datafile [ ( size ) ]
    This makes use of a high-performance cyclic buffer (approx. size bytes in size) inside a shared memory segment in RAM (established via /path/to/datafile ) to synchronize the local OpenSSL memory caches of the server processes. This is the recommended session cache. To use this, ensure that mod_socache_shmcb is loaded.

  • dc:UNIX:/path/to/socket
    This makes use of the distcache distributed session caching libraries. The argument should specify the location of the server or proxy to be used using the distcache address syntax; for example, UNIX:/path/to/socket specifies a UNIX domain socket (typically a local dc_client proxy); IP:server.example.com:9001 specifies an IP address. To use this, ensure that mod_socache_dc is loaded.

Examples

SSLSessionCache "dbm:/usr/local/apache/logs/ssl_gcache_data"
SSLSessionCache "shmcb:/usr/local/apache/logs/ssl_gcache_data(512000)"

The ssl-cache mutex is used to serialize access to the session cache to prevent corruption. This mutex can be configured using the Mutex directive.

SSLSessionCacheTimeout Directive

Description:Number of seconds before an SSL session expires in the Session Cache
Syntax:SSLSessionCacheTimeout seconds
Default:SSLSessionCacheTimeout 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Applies also to RFC 5077 TLS session resumption in Apache 2.4.10 and later

This directive sets the timeout in seconds for the information stored in the global/inter-process SSL Session Cache, the OpenSSL internal memory cache and for sessions resumed by TLS session resumption (RFC 5077). It can be set as low as 15 for testing, but should be set to higher values like 300 in real life.

Example

SSLSessionCacheTimeout 600

SSLSessionTicketKeyFile Directive

Description:Persistent encryption/decryption key for TLS session tickets
Syntax:SSLSessionTicketKeyFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.0 and later, if using OpenSSL 0.9.8h or later

Optionally configures a secret key for encrypting and decrypting TLS session tickets, as defined in RFC 5077. Primarily suitable for clustered environments where TLS sessions information should be shared between multiple nodes. For single-instance httpd setups, it is recommended to not configure a ticket key file, but to rely on (random) keys generated by mod_ssl at startup, instead.

The ticket key file must contain 48 bytes of random data, preferrably created from a high-entropy source. On a Unix-based system, a ticket key file can be created as follows:

dd if=/dev/random of=/path/to/file.tkey bs=1 count=48

Ticket keys should be rotated (replaced) on a frequent basis, as this is the only way to invalidate an existing session ticket - OpenSSL currently doesn't allow to specify a limit for ticket lifetimes. A new ticket key only gets used after restarting the web server. All existing session tickets become invalid after a restart.

The ticket key file contains sensitive keying material and should be protected with file permissions similar to those used for SSLCertificateKeyFile.

SSLSessionTickets Directive

Description:Enable or disable use of TLS session tickets
Syntax:SSLSessionTickets on\|off
Default:SSLSessionTickets on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.11 and later, if using OpenSSL 0.9.8f or later.

This directive allows to enable or disable the use of TLS session tickets (RFC 5077).

TLS session tickets are enabled by default. Using them without restarting the web server with an appropriate frequency (e.g. daily) compromises perfect forward secrecy.

SSLSRPUnknownUserSeed Directive

Description:SRP unknown user seed
Syntax:SSLSRPUnknownUserSeed secret-string
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or later

This directive sets the seed used to fake SRP user parameters for unknown users, to avoid leaking whether a given user exists. Specify a secret string. If this directive is not used, then Apache will return the UNKNOWN_PSK_IDENTITY alert to clients who specify an unknown username.

Example

SSLSRPUnknownUserSeed "secret"

SSLSRPVerifierFile Directive

Description:Path to SRP verifier file
Syntax:SSLSRPVerifierFile file-path
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or later

This directive enables TLS-SRP and sets the path to the OpenSSL SRP (Secure Remote Password) verifier file containing TLS-SRP usernames, verifiers, salts, and group parameters.

Example

SSLSRPVerifierFile "/path/to/file.srpv"

The verifier file can be created with the openssl command line utility:

Creating the SRP verifier file

openssl srp -srpvfile passwd.srpv -userinfo "some info" -add username

The value given with the optional -userinfo parameter is avalable in the SSL_SRP_USERINFO request environment variable.

SSLStaplingCache Directive

Description:Configures the OCSP stapling cache
Syntax:SSLStaplingCache type
Context:server config
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Configures the cache used to store OCSP responses which get included in the TLS handshake if SSLUseStapling is enabled. Configuration of a cache is mandatory for OCSP stapling. With the exception of none and nonenotnull , the same storage types are supported as with SSLSessionCache.

SSLStaplingErrorCacheTimeout Directive

Description:Number of seconds before expiring invalid responses in the OCSP stapling cache
Syntax:SSLStaplingErrorCacheTimeout seconds
Default:SSLStaplingErrorCacheTimeout 600
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Sets the timeout in seconds before invalid responses in the OCSP stapling cache (configured through SSLStaplingCache) will expire. To set the cache timeout for valid responses, see SSLStaplingStandardCacheTimeout.

SSLStaplingFakeTryLater Directive

Description:Synthesize "tryLater" responses for failed OCSP stapling queries
Syntax:SSLStaplingFakeTryLater on\|off
Default:SSLStaplingFakeTryLater on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

When enabled and a query to an OCSP responder for stapling purposes fails, mod_ssl will synthesize a "tryLater" response for the client. Only effective if SSLStaplingReturnResponderErrors is also enabled.

SSLStaplingForceURL Directive

Description:Override the OCSP responder URI specified in the certificate's AIA extension
Syntax:SSLStaplingForceURL uri
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This directive overrides the URI of an OCSP responder as obtained from the authorityInfoAccess (AIA) extension of the certificate. One potential use is when a proxy is used for retrieving OCSP queries.

SSLStaplingResponderTimeout Directive

Description:Timeout for OCSP stapling queries
Syntax:SSLStaplingResponderTimeout seconds
Default:SSLStaplingResponderTimeout 10
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the timeout for queries to OCSP responders when SSLUseStapling is enabled and mod_ssl is querying a responder for OCSP stapling purposes.

SSLStaplingResponseMaxAge Directive

Description:Maximum allowable age for OCSP stapling responses
Syntax:SSLStaplingResponseMaxAge seconds
Default:SSLStaplingResponseMaxAge -1
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the maximum allowable age ("freshness") when considering OCSP responses for stapling purposes, i.e. when SSLUseStapling is turned on. The default value ( -1 ) does not enforce a maximum age, which means that OCSP responses are considered valid as long as their nextUpdate field is in the future.

SSLStaplingResponseTimeSkew Directive

Description:Maximum allowable time skew for OCSP stapling response validation
Syntax:SSLStaplingResponseTimeSkew seconds
Default:SSLStaplingResponseTimeSkew 300
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option sets the maximum allowable time skew when mod_ssl checks the thisUpdate and nextUpdate fields of OCSP responses which get included in the TLS handshake (OCSP stapling). Only applicable if SSLUseStapling is turned on.

SSLStaplingReturnResponderErrors Directive

Description:Pass stapling related OCSP errors on to client
Syntax:SSLStaplingReturnResponderErrors on\|off
Default:SSLStaplingReturnResponderErrors on
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

When enabled, mod_ssl will pass responses from unsuccessful stapling related OCSP queries (such as responses with an overall status other than "successful", responses with a certificate status other than "good", expired responses etc.) on to the client. If set to off , only responses indicating a certificate status of "good" will be included in the TLS handshake.

SSLStaplingStandardCacheTimeout Directive

Description:Number of seconds before expiring responses in the OCSP stapling cache
Syntax:SSLStaplingStandardCacheTimeout seconds
Default:SSLStaplingStandardCacheTimeout 3600
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

Sets the timeout in seconds before responses in the OCSP stapling cache (configured through SSLStaplingCache) will expire. This directive applies to valid responses, while SSLStaplingErrorCacheTimeout is used for controlling the timeout for invalid/unavailable responses.

SSLStrictSNIVHostCheck Directive

Description:Whether to allow non-SNI clients to access a name-based virtual host.
Syntax:SSLStrictSNIVHostCheck on\|off
Default:SSLStrictSNIVHostCheck off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available in Apache 2.2.12 and later

This directive sets whether a non-SNI client is allowed to access a name-based virtual host. If set to on in the default name-based virtual host, clients that are SNI unaware will not be allowed to access any virtual host, belonging to this particular IP / port combination. If set to on in any other virtual host, SNI unaware clients are not allowed to access this particular virtual host.

This option is only available if httpd was compiled against an SNI capable version of OpenSSL.

Example

SSLStrictSNIVHostCheck on

SSLUserName Directive

Description:Variable name to determine user name
Syntax:SSLUserName varname
Context:server config, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

This directive sets the "user" field in the Apache request object. This is used by lower modules to identify the user with a character string. In particular, this may cause the environment variable REMOTE_USER to be set. The varname can be any of the SSL environment variables.

Note that this directive has no effect if the FakeBasicAuth option is used (see SSLOptions).

Example

SSLUserName SSL_CLIENT_S_DN_CN

SSLUseStapling Directive

Description:Enable stapling of OCSP responses in the TLS handshake
Syntax:SSLUseStapling on\|off
Default:SSLUseStapling off
Context:server config, virtual host
Status:Extension
Module:mod_ssl
Compatibility:Available if using OpenSSL 0.9.8h or later

This option enables OCSP stapling, as defined by the "Certificate Status Request" TLS extension specified in RFC 6066. If enabled (and requested by the client), mod_ssl will include an OCSP response for its own certificate in the TLS handshake. Configuring an SSLStaplingCache is a prerequisite for enabling OCSP stapling.

OCSP stapling relieves the client of querying the OCSP responder on its own, but it should be noted that with the RFC 6066 specification, the server's CertificateStatus reply may only include an OCSP response for a single cert. For server certificates with intermediate CA certificates in their chain (the typical case nowadays), stapling in its current implementation therefore only partially achieves the stated goal of "saving roundtrips and resources" - see also RFC 6961 (TLS Multiple Certificate Status Extension).

When OCSP stapling is enabled, the ssl-stapling mutex is used to control access to the OCSP stapling cache in order to prevent corruption, and the sss-stapling-refresh mutex is used to control refreshes of OCSP responses. These mutexes can be configured using the Mutex directive.

SSLVerifyClient Directive

Description:Type of Client Certificate verification
Syntax:SSLVerifyClient level
Default:SSLVerifyClient none
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

This directive sets the Certificate verification level for the Client Authentication. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the client authentication process used in the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotiation with the reconfigured client verification level after the HTTP request was read but before the HTTP response is sent.

The following levels are available for level:

  • none : no client Certificate is required at all

  • optional : the client may present a valid Certificate

  • require : the client has to present a valid Certificate

  • optional_no_ca : the client may present a valid Certificate
    but it need not to be (successfully) verifiable. This option cannot be relied upon for client authentication.

Example

SSLVerifyClient require

SSLVerifyDepth Directive

Description:Maximum depth of CA Certificates in Client Certificate verification
Syntax:SSLVerifyDepth number
Default:SSLVerifyDepth 1
Context:server config, virtual host, directory, .htaccess
Override:AuthConfig
Status:Extension
Module:mod_ssl

This directive sets how deeply mod_ssl should verify before deciding that the clients don't have a valid certificate. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the client authentication process used in the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotiation with the reconfigured client verification depth after the HTTP request was read but before the HTTP response is sent.

The depth actually is the maximum number of intermediate certificate issuers, i.e. the number of CA certificates which are max allowed to be followed while verifying the client certificate. A depth of 0 means that self-signed client certificates are accepted only, the default depth of 1 means the client certificate can be self-signed or has to be signed by a CA which is directly known to the server (i.e. the CA's certificate is under SSLCACertificatePath), etc.

Example

SSLVerifyDepth 10
Updated at: 9 months ago
Run-time Configuration DirectivesTable of contentMulti-Processing Modules (MPMs)