On this page
ssl — TLS/SSL wrapper for socket objects
Source code: Lib/ssl.py
This module provides access to Transport Layer Security (often known as “Secure Sockets Layer”) encryption and peer authentication facilities for network sockets, both client-side and server-side. This module uses the OpenSSL library. It is available on all modern Unix systems, Windows, Mac OS X, and probably additional platforms, as long as OpenSSL is installed on that platform.
Note
Some behavior may be platform dependent, since calls are made to the operating system socket APIs. The installed version of OpenSSL may also cause variations in behavior. For example, TLSv1.1 and TLSv1.2 come with openssl version 1.0.1.
Warning
Don’t use this module without reading the Security considerations. Doing so may lead to a false sense of security, as the default settings of the ssl module are not necessarily appropriate for your application.
This section documents the objects and functions in the ssl
module; for more general information about TLS, SSL, and certificates, the reader is referred to the documents in the “See Also” section at the bottom.
This module provides a class, ssl.SSLSocket
, which is derived from the socket.socket
type, and provides a socket-like wrapper that also encrypts and decrypts the data going over the socket with SSL. It supports additional methods such as getpeercert()
, which retrieves the certificate of the other side of the connection, and cipher()
, which retrieves the cipher being used for the secure connection.
For more sophisticated applications, the ssl.SSLContext
class helps manage settings and certificates, which can then be inherited by SSL sockets created through the SSLContext.wrap_socket()
method.
Changed in version 3.5.3: Updated to support linking with OpenSSL 1.1.0
Changed in version 3.6: OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported. In the future the ssl module will require at least OpenSSL 1.0.2 or 1.1.0.
Functions, Constants, and Exceptions
Socket creation
Since Python 3.2 and 2.7.9, it is recommended to use the SSLContext.wrap_socket()
of an SSLContext
instance to wrap sockets as SSLSocket
objects. The helper functions create_default_context()
returns a new context with secure default settings. The old wrap_socket()
function is deprecated since it is both inefficient and has no support for server name indication (SNI) and hostname matching.
Client socket example with default context and IPv4/IPv6 dual stack:
import socket
import ssl
hostname = 'www.python.org'
context = ssl.create_default_context()
with socket.create_connection((hostname, 443)) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Client socket example with custom context and IPv4:
hostname = 'www.python.org'
# PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.load_verify_locations('path/to/cabundle.pem')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Server socket example listening on localhost IPv4:
context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
sock.bind(('127.0.0.1', 8443))
sock.listen(5)
with context.wrap_socket(sock, server_side=True) as ssock:
conn, addr = ssock.accept()
...
Context creation
A convenience function helps create SSLContext
objects for common purposes.
ssl.
create_default_context
( purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None )-
Return a new
SSLContext
object with default settings for the given purpose. The settings are chosen by thessl
module, and usually represent a higher security level than when calling theSSLContext
constructor directly.cafile, capath, cadata represent optional CA certificates to trust for certificate verification, as in
SSLContext.load_verify_locations()
. If all three areNone
, this function can choose to trust the system’s default CA certificates instead.The settings are:
PROTOCOL_TLS
,OP_NO_SSLv2
, andOP_NO_SSLv3
with high encryption cipher suites without RC4 and without unauthenticated cipher suites. PassingSERVER_AUTH
as purpose setsverify_mode
toCERT_REQUIRED
and either loads CA certificates (when at least one of cafile, capath or cadata is given) or usesSSLContext.load_default_certs()
to load default CA certificates.When
keylog_filename
is supported and the environment variableSSLKEYLOGFILE
is set,create_default_context()
enables key logging.Note
The protocol, options, cipher and other settings may change to more restrictive values anytime without prior deprecation. The values represent a fair balance between compatibility and security.
If your application needs specific settings, you should create a
SSLContext
and apply the settings yourself.Note
If you find that when certain older clients or servers attempt to connect with a
SSLContext
created by this function that they get an error stating “Protocol or cipher suite mismatch”, it may be that they only support SSL3.0 which this function excludes using theOP_NO_SSLv3
. SSL3.0 is widely considered to be completely broken . If you still wish to continue to use this function but still allow SSL 3.0 connections you can re-enable them using:ctx = ssl.create_default_context(Purpose.CLIENT_AUTH) ctx.options &= ~ssl.OP_NO_SSLv3
New in version 3.4.
Changed in version 3.4.4: RC4 was dropped from the default cipher string.
Changed in version 3.6: ChaCha20/Poly1305 was added to the default cipher string.
3DES was dropped from the default cipher string.
Changed in version 3.8: Support for key logging to
SSLKEYLOGFILE
was added.
Exceptions
- exception
ssl.
SSLError
-
Raised to signal an error from the underlying SSL implementation (currently provided by the OpenSSL library). This signifies some problem in the higher-level encryption and authentication layer that’s superimposed on the underlying network connection. This error is a subtype of
OSError
. The error code and message ofSSLError
instances are provided by the OpenSSL library.Changed in version 3.3:
SSLError
used to be a subtype ofsocket.error
.
- exception
ssl.
SSLZeroReturnError
-
A subclass of
SSLError
raised when trying to read or write and the SSL connection has been closed cleanly. Note that this doesn’t mean that the underlying transport (read TCP) has been closed.New in version 3.3.
- exception
ssl.
SSLWantReadError
-
A subclass of
SSLError
raised by a non-blocking SSL socket when trying to read or write data, but more data needs to be received on the underlying TCP transport before the request can be fulfilled.New in version 3.3.
- exception
ssl.
SSLWantWriteError
-
A subclass of
SSLError
raised by a non-blocking SSL socket when trying to read or write data, but more data needs to be sent on the underlying TCP transport before the request can be fulfilled.New in version 3.3.
- exception
ssl.
SSLSyscallError
-
A subclass of
SSLError
raised when a system error was encountered while trying to fulfill an operation on a SSL socket. Unfortunately, there is no easy way to inspect the original errno number.New in version 3.3.
- exception
ssl.
SSLEOFError
-
A subclass of
SSLError
raised when the SSL connection has been terminated abruptly. Generally, you shouldn’t try to reuse the underlying transport when this error is encountered.New in version 3.3.
- exception
ssl.
SSLCertVerificationError
-
A subclass of
SSLError
raised when certificate validation has failed.New in version 3.7.
- exception
ssl.
CertificateError
-
An alias for
SSLCertVerificationError
.Changed in version 3.7: The exception is now an alias for
SSLCertVerificationError
.
Random generation
ssl.
RAND_bytes
( num )-
Return num cryptographically strong pseudo-random bytes. Raises an
SSLError
if the PRNG has not been seeded with enough data or if the operation is not supported by the current RAND method.RAND_status()
can be used to check the status of the PRNG andRAND_add()
can be used to seed the PRNG.For almost all applications
os.urandom()
is preferable.Read the Wikipedia article, Cryptographically secure pseudorandom number generator (CSPRNG) , to get the requirements of a cryptographically generator.
New in version 3.3.
ssl.
RAND_pseudo_bytes
( num )-
Return (bytes, is_cryptographic): bytes are num pseudo-random bytes, is_cryptographic is
True
if the bytes generated are cryptographically strong. Raises anSSLError
if the operation is not supported by the current RAND method.Generated pseudo-random byte sequences will be unique if they are of sufficient length, but are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.
For almost all applications
os.urandom()
is preferable.New in version 3.3.
Deprecated since version 3.6: OpenSSL has deprecated
ssl.RAND_pseudo_bytes()
, usessl.RAND_bytes()
instead.
ssl.
RAND_status
( )-
Return
True
if the SSL pseudo-random number generator has been seeded with ‘enough’ randomness, andFalse
otherwise. You can usessl.RAND_egd()
andssl.RAND_add()
to increase the randomness of the pseudo-random number generator.
ssl.
RAND_egd
( path )-
If you are running an entropy-gathering daemon (EGD) somewhere, and path is the pathname of a socket connection open to it, this will read 256 bytes of randomness from the socket, and add it to the SSL pseudo-random number generator to increase the security of generated secret keys. This is typically only necessary on systems without better sources of randomness.
See http://egd.sourceforge.net/ or http://prngd.sourceforge.net/ for sources of entropy-gathering daemons.
Availability: not available with LibreSSL and OpenSSL > 1.1.0.
ssl.
RAND_add
( bytes, entropy )-
Mix the given bytes into the SSL pseudo-random number generator. The parameter entropy (a float) is a lower bound on the entropy contained in string (so you can always use
0.0
). See RFC 1750 for more information on sources of entropy.Changed in version 3.5: Writable bytes-like object is now accepted.
Certificate handling
ssl.
match_hostname
( cert, hostname )-
Verify that cert (in decoded format as returned by
SSLSocket.getpeercert()
) matches the given hostname. The rules applied are those for checking the identity of HTTPS servers as outlined in RFC 2818 , RFC 5280 and RFC 6125 . In addition to HTTPS, this function should be suitable for checking the identity of servers in various SSL-based protocols such as FTPS, IMAPS, POPS and others.CertificateError
is raised on failure. On success, the function returns nothing:>>> cert = {'subject': ((('commonName', 'example.com'),),)} >>> ssl.match_hostname(cert, "example.com") >>> ssl.match_hostname(cert, "example.org") Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/py3k/Lib/ssl.py", line 130, in match_hostname ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'
New in version 3.2.
Changed in version 3.3.3: The function now follows RFC 6125 , section 6.4.3 and does neither match multiple wildcards (e.g.
*.*.com
or*a*.example.org
) nor a wildcard inside an internationalized domain names (IDN) fragment. IDN A-labels such aswww*.xn--pthon-kva.org
are still supported, butx*.python.org
no longer matchesxn--tda.python.org
.Changed in version 3.5: Matching of IP addresses, when present in the subjectAltName field of the certificate, is now supported.
Changed in version 3.7: The function is no longer used to TLS connections. Hostname matching is now performed by OpenSSL.
Allow wildcard when it is the leftmost and the only character in that segment. Partial wildcards like
www*.example.com
are no longer supported.Deprecated since version 3.7.
ssl.
cert_time_to_seconds
( cert_time )-
Return the time in seconds since the Epoch, given the
cert_time
string representing the “notBefore” or “notAfter” date from a certificate in"%b %d %H:%M:%S %Y %Z"
strptime format (C locale).Here’s an example:
>>> import ssl >>> timestamp = ssl.cert_time_to_seconds("Jan 5 09:34:43 2018 GMT") >>> timestamp 1515144883 >>> from datetime import datetime >>> print(datetime.utcfromtimestamp(timestamp)) 2018-01-05 09:34:43
“notBefore” or “notAfter” dates must use GMT (RFC 5280 ).
Changed in version 3.5: Interpret the input time as a time in UTC as specified by ‘GMT’ timezone in the input string. Local timezone was used previously. Return an integer (no fractions of a second in the input format)
ssl.
get_server_certificate
( addr, ssl_version=PROTOCOL_TLS, ca_certs=None )-
Given the address
addr
of an SSL-protected server, as a (hostname, port-number) pair, fetches the server’s certificate, and returns it as a PEM-encoded string. Ifssl_version
is specified, uses that version of the SSL protocol to attempt to connect to the server. Ifca_certs
is specified, it should be a file containing a list of root certificates, the same format as used for the same parameter inSSLContext.wrap_socket()
. The call will attempt to validate the server certificate against that set of root certificates, and will fail if the validation attempt fails.Changed in version 3.3: This function is now IPv6-compatible.
Changed in version 3.5: The default ssl_version is changed from
PROTOCOL_SSLv3
toPROTOCOL_TLS
for maximum compatibility with modern servers.
ssl.
DER_cert_to_PEM_cert
( DER_cert_bytes )-
Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded string version of the same certificate.
ssl.
PEM_cert_to_DER_cert
( PEM_cert_string )-
Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of bytes for that same certificate.
ssl.
get_default_verify_paths
( )-
Returns a named tuple with paths to OpenSSL’s default cafile and capath. The paths are the same as used by
SSLContext.set_default_verify_paths()
. The return value is a named tupleDefaultVerifyPaths
:cafile
- resolved path to cafile orNone
if the file doesn’t exist,capath
- resolved path to capath orNone
if the directory doesn’t exist,openssl_cafile_env
- OpenSSL’s environment key that points to a cafile,openssl_cafile
- hard coded path to a cafile,openssl_capath_env
- OpenSSL’s environment key that points to a capath,openssl_capath
- hard coded path to a capath directory
Availability: LibreSSL ignores the environment vars
openssl_cafile_env
andopenssl_capath_env
.New in version 3.4.
ssl.
enum_certificates
( store_name )-
Retrieve certificates from Windows’ system cert store. store_name may be one of
CA
,ROOT
orMY
. Windows may provide additional cert stores, too.The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either
x509_asn
for X.509 ASN.1 data orpkcs_7_asn
for PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set of OIDS or exactlyTrue
if the certificate is trustworthy for all purposes.Example:
>>> ssl.enum_certificates("CA") [(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}), (b'data...', 'x509_asn', True)]
Availability: Windows.
New in version 3.4.
ssl.
enum_crls
( store_name )-
Retrieve CRLs from Windows’ system cert store. store_name may be one of
CA
,ROOT
orMY
. Windows may provide additional cert stores, too.The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either
x509_asn
for X.509 ASN.1 data orpkcs_7_asn
for PKCS#7 ASN.1 data.Availability: Windows.
New in version 3.4.
ssl.
wrap_socket
( sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version=PROTOCOL_TLS, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None )-
Takes an instance
sock
ofsocket.socket
, and returns an instance ofssl.SSLSocket
, a subtype ofsocket.socket
, which wraps the underlying socket in an SSL context.sock
must be aSOCK_STREAM
socket; other socket types are unsupported.Internally, function creates a
SSLContext
with protocol ssl_version andSSLContext.options
set to cert_reqs. If parameters keyfile, certfile, ca_certs or ciphers are set, then the values are passed toSSLContext.load_cert_chain()
,SSLContext.load_verify_locations()
, andSSLContext.set_ciphers()
.The arguments server_side, do_handshake_on_connect, and suppress_ragged_eofs have the same meaning as
SSLContext.wrap_socket()
.Deprecated since version 3.7: Since Python 3.2 and 2.7.9, it is recommended to use the
SSLContext.wrap_socket()
instead ofwrap_socket()
. The top-level function is limited and creates an insecure client socket without server name indication or hostname matching.
Constants
All constants are now
enum.IntEnum
orenum.IntFlag
collections.New in version 3.6.
ssl.
CERT_NONE
-
Possible value for
SSLContext.verify_mode
, or thecert_reqs
parameter towrap_socket()
. Except forPROTOCOL_TLS_CLIENT
, it is the default mode. With client-side sockets, just about any cert is accepted. Validation errors, such as untrusted or expired cert, are ignored and do not abort the TLS/SSL handshake.In server mode, no certificate is requested from the client, so the client does not send any for client cert authentication.
See the discussion of Security considerations below.
ssl.
CERT_OPTIONAL
-
Possible value for
SSLContext.verify_mode
, or thecert_reqs
parameter towrap_socket()
. In client mode,CERT_OPTIONAL
has the same meaning asCERT_REQUIRED
. It is recommended to useCERT_REQUIRED
for client-side sockets instead.In server mode, a client certificate request is sent to the client. The client may either ignore the request or send a certificate in order perform TLS client cert authentication. If the client chooses to send a certificate, it is verified. Any verification error immediately aborts the TLS handshake.
Use of this setting requires a valid set of CA certificates to be passed, either to
SSLContext.load_verify_locations()
or as a value of theca_certs
parameter towrap_socket()
.
ssl.
CERT_REQUIRED
-
Possible value for
SSLContext.verify_mode
, or thecert_reqs
parameter towrap_socket()
. In this mode, certificates are required from the other side of the socket connection; anSSLError
will be raised if no certificate is provided, or if its validation fails. This mode is not sufficient to verify a certificate in client mode as it does not match hostnames.check_hostname
must be enabled as well to verify the authenticity of a cert.PROTOCOL_TLS_CLIENT
usesCERT_REQUIRED
and enablescheck_hostname
by default.With server socket, this mode provides mandatory TLS client cert authentication. A client certificate request is sent to the client and the client must provide a valid and trusted certificate.
Use of this setting requires a valid set of CA certificates to be passed, either to
SSLContext.load_verify_locations()
or as a value of theca_certs
parameter towrap_socket()
.
- class
ssl.
VerifyMode
-
enum.IntEnum
collection of CERT_* constants.New in version 3.6.
ssl.
VERIFY_DEFAULT
-
Possible value for
SSLContext.verify_flags
. In this mode, certificate revocation lists (CRLs) are not checked. By default OpenSSL does neither require nor verify CRLs.New in version 3.4.
ssl.
VERIFY_CRL_CHECK_LEAF
-
Possible value for
SSLContext.verify_flags
. In this mode, only the peer cert is checked but none of the intermediate CA certificates. The mode requires a valid CRL that is signed by the peer cert’s issuer (its direct ancestor CA). If no proper CRL has has been loaded withSSLContext.load_verify_locations
, validation will fail.New in version 3.4.
ssl.
VERIFY_CRL_CHECK_CHAIN
-
Possible value for
SSLContext.verify_flags
. In this mode, CRLs of all certificates in the peer cert chain are checked.New in version 3.4.
ssl.
VERIFY_X509_STRICT
-
Possible value for
SSLContext.verify_flags
to disable workarounds for broken X.509 certificates.New in version 3.4.
ssl.
VERIFY_X509_TRUSTED_FIRST
-
Possible value for
SSLContext.verify_flags
. It instructs OpenSSL to prefer trusted certificates when building the trust chain to validate a certificate. This flag is enabled by default.New in version 3.4.4.
- class
ssl.
VerifyFlags
-
enum.IntFlag
collection of VERIFY_* constants.New in version 3.6.
ssl.
PROTOCOL_TLS
-
Selects the highest protocol version that both the client and server support. Despite the name, this option can select both “SSL” and “TLS” protocols.
New in version 3.6.
ssl.
PROTOCOL_TLS_CLIENT
-
Auto-negotiate the highest protocol version like
PROTOCOL_TLS
, but only support client-sideSSLSocket
connections. The protocol enablesCERT_REQUIRED
andcheck_hostname
by default.New in version 3.6.
ssl.
PROTOCOL_TLS_SERVER
-
Auto-negotiate the highest protocol version like
PROTOCOL_TLS
, but only support server-sideSSLSocket
connections.New in version 3.6.
ssl.
PROTOCOL_SSLv23
-
Alias for
PROTOCOL_TLS
.Deprecated since version 3.6: Use
PROTOCOL_TLS
instead.
ssl.
PROTOCOL_SSLv2
-
Selects SSL version 2 as the channel encryption protocol.
This protocol is not available if OpenSSL is compiled with the
OPENSSL_NO_SSL2
flag.Warning
SSL version 2 is insecure. Its use is highly discouraged.
Deprecated since version 3.6: OpenSSL has removed support for SSLv2.
ssl.
PROTOCOL_SSLv3
-
Selects SSL version 3 as the channel encryption protocol.
This protocol is not be available if OpenSSL is compiled with the
OPENSSL_NO_SSLv3
flag.Warning
SSL version 3 is insecure. Its use is highly discouraged.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default protocol
PROTOCOL_TLS
with flags likeOP_NO_SSLv3
instead.
ssl.
PROTOCOL_TLSv1
-
Selects TLS version 1.0 as the channel encryption protocol.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default protocol
PROTOCOL_TLS
with flags likeOP_NO_SSLv3
instead.
ssl.
PROTOCOL_TLSv1_1
-
Selects TLS version 1.1 as the channel encryption protocol. Available only with openssl version 1.0.1+.
New in version 3.4.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default protocol
PROTOCOL_TLS
with flags likeOP_NO_SSLv3
instead.
ssl.
PROTOCOL_TLSv1_2
-
Selects TLS version 1.2 as the channel encryption protocol. This is the most modern version, and probably the best choice for maximum protection, if both sides can speak it. Available only with openssl version 1.0.1+.
New in version 3.4.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default protocol
PROTOCOL_TLS
with flags likeOP_NO_SSLv3
instead.
ssl.
OP_ALL
-
Enables workarounds for various bugs present in other SSL implementations. This option is set by default. It does not necessarily set the same flags as OpenSSL’s
SSL_OP_ALL
constant.New in version 3.2.
ssl.
OP_NO_SSLv2
-
Prevents an SSLv2 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing SSLv2 as the protocol version.New in version 3.2.
Deprecated since version 3.6: SSLv2 is deprecated
ssl.
OP_NO_SSLv3
-
Prevents an SSLv3 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing SSLv3 as the protocol version.New in version 3.2.
Deprecated since version 3.6: SSLv3 is deprecated
ssl.
OP_NO_TLSv1
-
Prevents a TLSv1 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing TLSv1 as the protocol version.New in version 3.2.
Deprecated since version 3.7: The option is deprecated since OpenSSL 1.1.0, use the new
SSLContext.minimum_version
andSSLContext.maximum_version
instead.
ssl.
OP_NO_TLSv1_1
-
Prevents a TLSv1.1 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.1 as the protocol version. Available only with openssl version 1.0.1+.New in version 3.4.
Deprecated since version 3.7: The option is deprecated since OpenSSL 1.1.0.
ssl.
OP_NO_TLSv1_2
-
Prevents a TLSv1.2 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.2 as the protocol version. Available only with openssl version 1.0.1+.New in version 3.4.
Deprecated since version 3.7: The option is deprecated since OpenSSL 1.1.0.
ssl.
OP_NO_TLSv1_3
-
Prevents a TLSv1.3 connection. This option is only applicable in conjunction with
PROTOCOL_TLS
. It prevents the peers from choosing TLSv1.3 as the protocol version. TLS 1.3 is available with OpenSSL 1.1.1 or later. When Python has been compiled against an older version of OpenSSL, the flag defaults to 0.New in version 3.7.
Deprecated since version 3.7: The option is deprecated since OpenSSL 1.1.0. It was added to 2.7.15, 3.6.3 and 3.7.0 for backwards compatibility with OpenSSL 1.0.2.
ssl.
OP_NO_RENEGOTIATION
-
Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest messages, and ignore renegotiation requests via ClientHello.
This option is only available with OpenSSL 1.1.0h and later.
New in version 3.7.
ssl.
OP_CIPHER_SERVER_PREFERENCE
-
Use the server’s cipher ordering preference, rather than the client’s. This option has no effect on client sockets and SSLv2 server sockets.
New in version 3.3.
ssl.
OP_SINGLE_DH_USE
-
Prevents re-use of the same DH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
New in version 3.3.
ssl.
OP_SINGLE_ECDH_USE
-
Prevents re-use of the same ECDH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
New in version 3.3.
ssl.
OP_ENABLE_MIDDLEBOX_COMPAT
-
Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make a TLS 1.3 connection look more like a TLS 1.2 connection.
This option is only available with OpenSSL 1.1.1 and later.
New in version 3.8.
ssl.
OP_NO_COMPRESSION
-
Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.
This option is only available with OpenSSL 1.0.0 and later.
New in version 3.3.
- class
ssl.
Options
-
enum.IntFlag
collection of OP_* constants.
ssl.
HAS_ALPN
-
Whether the OpenSSL library has built-in support for the Application-Layer Protocol Negotiation TLS extension as described in RFC 7301 .
New in version 3.5.
ssl.
HAS_NEVER_CHECK_COMMON_NAME
-
Whether the OpenSSL library has built-in support not checking subject common name and
SSLContext.hostname_checks_common_name
is writeable.New in version 3.7.
ssl.
HAS_ECDH
-
Whether the OpenSSL library has built-in support for the Elliptic Curve-based Diffie-Hellman key exchange. This should be true unless the feature was explicitly disabled by the distributor.
New in version 3.3.
ssl.
HAS_SNI
-
Whether the OpenSSL library has built-in support for the Server Name Indication extension (as defined in RFC 6066 ).
New in version 3.2.
ssl.
HAS_NPN
-
Whether the OpenSSL library has built-in support for the Next Protocol Negotiation as described in the Application Layer Protocol Negotiation . When true, you can use the
SSLContext.set_npn_protocols()
method to advertise which protocols you want to support.New in version 3.3.
ssl.
HAS_SSLv2
-
Whether the OpenSSL library has built-in support for the SSL 2.0 protocol.
New in version 3.7.
ssl.
HAS_SSLv3
-
Whether the OpenSSL library has built-in support for the SSL 3.0 protocol.
New in version 3.7.
ssl.
HAS_TLSv1
-
Whether the OpenSSL library has built-in support for the TLS 1.0 protocol.
New in version 3.7.
ssl.
HAS_TLSv1_1
-
Whether the OpenSSL library has built-in support for the TLS 1.1 protocol.
New in version 3.7.
ssl.
HAS_TLSv1_2
-
Whether the OpenSSL library has built-in support for the TLS 1.2 protocol.
New in version 3.7.
ssl.
HAS_TLSv1_3
-
Whether the OpenSSL library has built-in support for the TLS 1.3 protocol.
New in version 3.7.
ssl.
CHANNEL_BINDING_TYPES
-
List of supported TLS channel binding types. Strings in this list can be used as arguments to
SSLSocket.get_channel_binding()
.New in version 3.3.
ssl.
OPENSSL_VERSION
-
The version string of the OpenSSL library loaded by the interpreter:
>>> ssl.OPENSSL_VERSION 'OpenSSL 1.0.2k 26 Jan 2017'
New in version 3.2.
ssl.
OPENSSL_VERSION_INFO
-
A tuple of five integers representing version information about the OpenSSL library:
>>> ssl.OPENSSL_VERSION_INFO (1, 0, 2, 11, 15)
New in version 3.2.
ssl.
OPENSSL_VERSION_NUMBER
-
The raw version number of the OpenSSL library, as a single integer:
>>> ssl.OPENSSL_VERSION_NUMBER 268443839 >>> hex(ssl.OPENSSL_VERSION_NUMBER) '0x100020bf'
New in version 3.2.
ssl.
ALERT_DESCRIPTION_HANDSHAKE_FAILURE
ssl.
ALERT_DESCRIPTION_INTERNAL_ERROR
ALERT_DESCRIPTION_*
-
Alert Descriptions from RFC 5246 and others. The IANA TLS Alert Registry contains this list and references to the RFCs where their meaning is defined.
Used as the return value of the callback function in
SSLContext.set_servername_callback()
.New in version 3.4.
- class
ssl.
AlertDescription
-
enum.IntEnum
collection of ALERT_DESCRIPTION_* constants.New in version 3.6.
Purpose.
SERVER_AUTH
-
Option for
create_default_context()
andSSLContext.load_default_certs()
. This value indicates that the context may be used to authenticate Web servers (therefore, it will be used to create client-side sockets).New in version 3.4.
Purpose.
CLIENT_AUTH
-
Option for
create_default_context()
andSSLContext.load_default_certs()
. This value indicates that the context may be used to authenticate Web clients (therefore, it will be used to create server-side sockets).New in version 3.4.
- class
ssl.
SSLErrorNumber
-
enum.IntEnum
collection of SSL_ERROR_* constants.New in version 3.6.
- class
ssl.
TLSVersion
-
enum.IntEnum
collection of SSL and TLS versions forSSLContext.maximum_version
andSSLContext.minimum_version
.New in version 3.7.
SSL Sockets
- class
ssl.
SSLSocket
( socket.socket ) -
SSL sockets provide the following methods of Socket Objects:
recv()
,recv_into()
(but passing a non-zeroflags
argument is not allowed)sendfile()
(butos.sendfile
will be used for plain-text sockets only, elsesend()
will be used)
However, since the SSL (and TLS) protocol has its own framing atop of TCP, the SSL sockets abstraction can, in certain respects, diverge from the specification of normal, OS-level sockets. See especially the notes on non-blocking sockets.
Instances of
SSLSocket
must be created using theSSLContext.wrap_socket()
method.Changed in version 3.5: The
sendfile()
method was added.Changed in version 3.5: The
shutdown()
does not reset the socket timeout each time bytes are received or sent. The socket timeout is now to maximum total duration of the shutdown.Deprecated since version 3.6: It is deprecated to create a
SSLSocket
instance directly, useSSLContext.wrap_socket()
to wrap a socket.Changed in version 3.7:
SSLSocket
instances must to created withwrap_socket()
. In earlier versions, it was possible to create instances directly. This was never documented or officially supported.
SSL sockets also have the following additional methods and attributes:
SSLSocket.
read
( len=1024, buffer=None )-
Read up to len bytes of data from the SSL socket and return the result as a
bytes
instance. If buffer is specified, then read into the buffer instead, and return the number of bytes read.Raise
SSLWantReadError
orSSLWantWriteError
if the socket is non-blocking and the read would block.As at any time a re-negotiation is possible, a call to
read()
can also cause write operations.Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to read up to len bytes.
Deprecated since version 3.6: Use
recv()
instead ofread()
.
SSLSocket.
write
( buf )-
Write buf to the SSL socket and return the number of bytes written. The buf argument must be an object supporting the buffer interface.
Raise
SSLWantReadError
orSSLWantWriteError
if the socket is non-blocking and the write would block.As at any time a re-negotiation is possible, a call to
write()
can also cause read operations.Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to write buf.
Deprecated since version 3.6: Use
send()
instead ofwrite()
.
Note
The read()
and write()
methods are the low-level methods that read and write unencrypted, application-level data and decrypt/encrypt it to encrypted, wire-level data. These methods require an active SSL connection, i.e. the handshake was completed and SSLSocket.unwrap()
was not called.
Normally you should use the socket API methods like recv()
and send()
instead of these methods.
SSLSocket.
do_handshake
( )-
Perform the SSL setup handshake.
Changed in version 3.4: The handshake method also performs
match_hostname()
when thecheck_hostname
attribute of the socket’scontext
is true.Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration of the handshake.
Changed in version 3.7: Hostname or IP address is matched by OpenSSL during handshake. The function
match_hostname()
is no longer used. In case OpenSSL refuses a hostname or IP address, the handshake is aborted early and a TLS alert message is send to the peer.
SSLSocket.
getpeercert
( binary_form=False )-
If there is no certificate for the peer on the other end of the connection, return
None
. If the SSL handshake hasn’t been done yet, raiseValueError
.If the
binary_form
parameter isFalse
, and a certificate was received from the peer, this method returns adict
instance. If the certificate was not validated, the dict is empty. If the certificate was validated, it returns a dict with several keys, amongst themsubject
(the principal for which the certificate was issued) andissuer
(the principal issuing the certificate). If a certificate contains an instance of the Subject Alternative Name extension (see RFC 3280 ), there will also be asubjectAltName
key in the dictionary.The
subject
andissuer
fields are tuples containing the sequence of relative distinguished names (RDNs) given in the certificate’s data structure for the respective fields, and each RDN is a sequence of name-value pairs. Here is a real-world example:{'issuer': ((('countryName', 'IL'),), (('organizationName', 'StartCom Ltd.'),), (('organizationalUnitName', 'Secure Digital Certificate Signing'),), (('commonName', 'StartCom Class 2 Primary Intermediate Server CA'),)), 'notAfter': 'Nov 22 08:15:19 2013 GMT', 'notBefore': 'Nov 21 03:09:52 2011 GMT', 'serialNumber': '95F0', 'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),), (('countryName', 'US'),), (('stateOrProvinceName', 'California'),), (('localityName', 'San Francisco'),), (('organizationName', 'Electronic Frontier Foundation, Inc.'),), (('commonName', '*.eff.org'),), (('emailAddress', 'hostmaster@eff.org'),)), 'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')), 'version': 3}
Note
To validate a certificate for a particular service, you can use the
match_hostname()
function.If the
binary_form
parameter isTrue
, and a certificate was provided, this method returns the DER-encoded form of the entire certificate as a sequence of bytes, orNone
if the peer did not provide a certificate. Whether the peer provides a certificate depends on the SSL socket’s role:for a client SSL socket, the server will always provide a certificate, regardless of whether validation was required;
for a server SSL socket, the client will only provide a certificate when requested by the server; therefore
getpeercert()
will returnNone
if you usedCERT_NONE
(rather thanCERT_OPTIONAL
orCERT_REQUIRED
).
Changed in version 3.2: The returned dictionary includes additional items such as
issuer
andnotBefore
.Changed in version 3.4:
ValueError
is raised when the handshake isn’t done. The returned dictionary includes additional X509v3 extension items such ascrlDistributionPoints
,caIssuers
andOCSP
URIs.Changed in version 3.8.1: IPv6 address strings no longer have a trailing new line.
SSLSocket.
cipher
( )-
Returns a three-value tuple containing the name of the cipher being used, the version of the SSL protocol that defines its use, and the number of secret bits being used. If no connection has been established, returns
None
.
-
Return the list of ciphers shared by the client during the handshake. Each entry of the returned list is a three-value tuple containing the name of the cipher, the version of the SSL protocol that defines its use, and the number of secret bits the cipher uses.
shared_ciphers()
returnsNone
if no connection has been established or the socket is a client socket.New in version 3.5.
SSLSocket.
compression
( )-
Return the compression algorithm being used as a string, or
None
if the connection isn’t compressed.If the higher-level protocol supports its own compression mechanism, you can use
OP_NO_COMPRESSION
to disable SSL-level compression.New in version 3.3.
SSLSocket.
get_channel_binding
( cb_type="tls-unique" )-
Get channel binding data for current connection, as a bytes object. Returns
None
if not connected or the handshake has not been completed.The cb_type parameter allow selection of the desired channel binding type. Valid channel binding types are listed in the
CHANNEL_BINDING_TYPES
list. Currently only the ‘tls-unique’ channel binding, defined by RFC 5929 , is supported.ValueError
will be raised if an unsupported channel binding type is requested.New in version 3.3.
SSLSocket.
selected_alpn_protocol
( )-
Return the protocol that was selected during the TLS handshake. If
SSLContext.set_alpn_protocols()
was not called, if the other party does not support ALPN, if this socket does not support any of the client’s proposed protocols, or if the handshake has not happened yet,None
is returned.New in version 3.5.
SSLSocket.
selected_npn_protocol
( )-
Return the higher-level protocol that was selected during the TLS/SSL handshake. If
SSLContext.set_npn_protocols()
was not called, or if the other party does not support NPN, or if the handshake has not yet happened, this will returnNone
.New in version 3.3.
SSLSocket.
unwrap
( )-
Performs the SSL shutdown handshake, which removes the TLS layer from the underlying socket, and returns the underlying socket object. This can be used to go from encrypted operation over a connection to unencrypted. The returned socket should always be used for further communication with the other side of the connection, rather than the original socket.
SSLSocket.
verify_client_post_handshake
( )-
Requests post-handshake authentication (PHA) from a TLS 1.3 client. PHA can only be initiated for a TLS 1.3 connection from a server-side socket, after the initial TLS handshake and with PHA enabled on both sides, see
SSLContext.post_handshake_auth
.The method does not perform a cert exchange immediately. The server-side sends a CertificateRequest during the next write event and expects the client to respond with a certificate on the next read event.
If any precondition isn’t met (e.g. not TLS 1.3, PHA not enabled), an
SSLError
is raised.Note
Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the method raises
NotImplementedError
.New in version 3.8.
SSLSocket.
version
( )-
Return the actual SSL protocol version negotiated by the connection as a string, or
None
is no secure connection is established. As of this writing, possible return values include"SSLv2"
,"SSLv3"
,"TLSv1"
,"TLSv1.1"
and"TLSv1.2"
. Recent OpenSSL versions may define more return values.New in version 3.5.
SSLSocket.
pending
( )-
Returns the number of already decrypted bytes available for read, pending on the connection.
SSLSocket.
context
-
The
SSLContext
object this SSL socket is tied to. If the SSL socket was created using the deprecatedwrap_socket()
function (rather thanSSLContext.wrap_socket()
), this is a custom context object created for this SSL socket.New in version 3.2.
SSLSocket.
server_side
-
A boolean which is
True
for server-side sockets andFalse
for client-side sockets.New in version 3.2.
SSLSocket.
server_hostname
-
Hostname of the server:
str
type, orNone
for server-side socket or if the hostname was not specified in the constructor.New in version 3.2.
Changed in version 3.7: The attribute is now always ASCII text. When
server_hostname
is an internationalized domain name (IDN), this attribute now stores the A-label form ("xn--pythn-mua.org"
), rather than the U-label form ("pythön.org"
).
SSLSocket.
session
-
The
SSLSession
for this SSL connection. The session is available for client and server side sockets after the TLS handshake has been performed. For client sockets the session can be set beforedo_handshake()
has been called to reuse a session.New in version 3.6.
SSL Contexts
New in version 3.2.
An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.
- class
ssl.
SSLContext
( protocol=PROTOCOL_TLS ) -
Create a new SSL context. You may pass protocol which must be one of the
PROTOCOL_*
constants defined in this module. The parameter specifies which version of the SSL protocol to use. Typically, the server chooses a particular protocol version, and the client must adapt to the server’s choice. Most of the versions are not interoperable with the other versions. If not specified, the default isPROTOCOL_TLS
; it provides the most compatibility with other versions.Here’s a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):
Footnotes
- 1 (1,2)
-
SSLContext
disables SSLv2 withOP_NO_SSLv2
by default. - 2 (1,2)
-
SSLContext
disables SSLv3 withOP_NO_SSLv3
by default. - 3 (1,2)
-
TLS 1.3 protocol will be available with
PROTOCOL_TLS
in OpenSSL >= 1.1.1. There is no dedicated PROTOCOL constant for just TLS 1.3.
See also
create_default_context()
lets thessl
module choose security settings for a given purpose.Changed in version 3.6: The context is created with secure default values. The options
OP_NO_COMPRESSION
,OP_CIPHER_SERVER_PREFERENCE
,OP_SINGLE_DH_USE
,OP_SINGLE_ECDH_USE
,OP_NO_SSLv2
(except forPROTOCOL_SSLv2
), andOP_NO_SSLv3
(except forPROTOCOL_SSLv3
) are set by default. The initial cipher suite list contains onlyHIGH
ciphers, noNULL
ciphers and noMD5
ciphers (except forPROTOCOL_SSLv2
).
SSLContext
objects have the following methods and attributes:
SSLContext.
cert_store_stats
( )-
Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.
Example for a context with one CA cert and one other cert:
>>> context.cert_store_stats() {'crl': 0, 'x509_ca': 1, 'x509': 2}
New in version 3.4.
SSLContext.
load_cert_chain
( certfile, keyfile=None, password=None )-
Load a private key and the corresponding certificate. The certfile string must be the path to a single file in PEM format containing the certificate as well as any number of CA certificates needed to establish the certificate’s authenticity. The keyfile string, if present, must point to a file containing the private key in. Otherwise the private key will be taken from certfile as well. See the discussion of Certificates for more information on how the certificate is stored in the certfile.
The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.
If the password argument is not specified and a password is required, OpenSSL’s built-in password prompting mechanism will be used to interactively prompt the user for a password.
An
SSLError
is raised if the private key doesn’t match with the certificate.Changed in version 3.3: New optional argument password.
SSLContext.
load_default_certs
( purpose=Purpose.SERVER_AUTH )-
Load a set of default “certification authority” (CA) certificates from default locations. On Windows it loads CA certs from the
CA
andROOT
system stores. On other systems it callsSSLContext.set_default_verify_paths()
. In the future the method may load CA certificates from other locations, too.The purpose flag specifies what kind of CA certificates are loaded. The default settings
Purpose.SERVER_AUTH
loads certificates, that are flagged and trusted for TLS web server authentication (client side sockets).Purpose.CLIENT_AUTH
loads CA certificates for client certificate verification on the server side.New in version 3.4.
SSLContext.
load_verify_locations
( cafile=None, capath=None, cadata=None )-
Load a set of “certification authority” (CA) certificates used to validate other peers’ certificates when
verify_mode
is other thanCERT_NONE
. At least one of cafile or capath must be specified.This method can also load certification revocation lists (CRLs) in PEM or DER format. In order to make use of CRLs,
SSLContext.verify_flags
must be configured properly.The cafile string, if present, is the path to a file of concatenated CA certificates in PEM format. See the discussion of Certificates for more information about how to arrange the certificates in this file.
The capath string, if present, is the path to a directory containing several CA certificates in PEM format, following an OpenSSL specific layout .
The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object of DER-encoded certificates. Like with capath extra lines around PEM-encoded certificates are ignored but at least one certificate must be present.
Changed in version 3.4: New optional argument cadata
SSLContext.
get_ca_certs
( binary_form=False )-
Get a list of loaded “certification authority” (CA) certificates. If the
binary_form
parameter isFalse
each list entry is a dict like the output ofSSLSocket.getpeercert()
. Otherwise the method returns a list of DER-encoded certificates. The returned list does not contain certificates from capath unless a certificate was requested and loaded by a SSL connection.Note
Certificates in a capath directory aren’t loaded unless they have been used at least once.
New in version 3.4.
SSLContext.
get_ciphers
( )-
Get a list of enabled ciphers. The list is in order of cipher priority. See
SSLContext.set_ciphers()
.Example:
>>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23) >>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA') >>> ctx.get_ciphers() # OpenSSL 1.0.x [{'alg_bits': 256, 'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA ' 'Enc=AESGCM(256) Mac=AEAD', 'id': 50380848, 'name': 'ECDHE-RSA-AES256-GCM-SHA384', 'protocol': 'TLSv1/SSLv3', 'strength_bits': 256}, {'alg_bits': 128, 'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA ' 'Enc=AESGCM(128) Mac=AEAD', 'id': 50380847, 'name': 'ECDHE-RSA-AES128-GCM-SHA256', 'protocol': 'TLSv1/SSLv3', 'strength_bits': 128}]
On OpenSSL 1.1 and newer the cipher dict contains additional fields:
>>> ctx.get_ciphers() # OpenSSL 1.1+ [{'aead': True, 'alg_bits': 256, 'auth': 'auth-rsa', 'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA ' 'Enc=AESGCM(256) Mac=AEAD', 'digest': None, 'id': 50380848, 'kea': 'kx-ecdhe', 'name': 'ECDHE-RSA-AES256-GCM-SHA384', 'protocol': 'TLSv1.2', 'strength_bits': 256, 'symmetric': 'aes-256-gcm'}, {'aead': True, 'alg_bits': 128, 'auth': 'auth-rsa', 'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA ' 'Enc=AESGCM(128) Mac=AEAD', 'digest': None, 'id': 50380847, 'kea': 'kx-ecdhe', 'name': 'ECDHE-RSA-AES128-GCM-SHA256', 'protocol': 'TLSv1.2', 'strength_bits': 128, 'symmetric': 'aes-128-gcm'}]
Availability: OpenSSL 1.0.2+.
New in version 3.6.
SSLContext.
set_default_verify_paths
( )-
Load a set of default “certification authority” (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there’s no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.
SSLContext.
set_ciphers
( ciphers )-
Set the available ciphers for sockets created with this context. It should be a string in the OpenSSL cipher list format . If no cipher can be selected (because compile-time options or other configuration forbids use of all the specified ciphers), an
SSLError
will be raised.Note
when connected, the
SSLSocket.cipher()
method of SSL sockets will give the currently selected cipher.OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default. The suites cannot be disabled with
set_ciphers()
.
SSLContext.
set_alpn_protocols
( protocols )-
Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of ASCII strings, like
['http/1.1', 'spdy/2']
, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to RFC 7301 . After a successful handshake, theSSLSocket.selected_alpn_protocol()
method will return the agreed-upon protocol.This method will raise
NotImplementedError
ifHAS_ALPN
isFalse
.OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise
SSLError
when both sides support ALPN but cannot agree on a protocol. 1.1.0f+ behaves like 1.0.2,SSLSocket.selected_alpn_protocol()
returns None.New in version 3.5.
SSLContext.
set_npn_protocols
( protocols )-
Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of strings, like
['http/1.1', 'spdy/2']
, ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to the Application Layer Protocol Negotiation . After a successful handshake, theSSLSocket.selected_npn_protocol()
method will return the agreed-upon protocol.This method will raise
NotImplementedError
ifHAS_NPN
isFalse
.New in version 3.3.
SSLContext.
sni_callback
-
Register a callback function that will be called after the TLS Client Hello handshake message has been received by the SSL/TLS server when the TLS client specifies a server name indication. The server name indication mechanism is specified in RFC 6066 section 3 - Server Name Indication.
Only one callback can be set per
SSLContext
. If sni_callback is set toNone
then the callback is disabled. Calling this function a subsequent time will disable the previously registered callback.The callback function will be called with three arguments; the first being the