35. Spring Security Crypto Module

35.1 Introduction

The Spring Security Crypto module provides support for symmetric encryption, key generation, and password encoding. The code is distributed as part of the core module but has no dependencies on any other Spring Security (or Spring) code.

35.2 Encryptors

The Encryptors class provides factory methods for constructing symmetric encryptors. Using this class, you can create ByteEncryptors to encrypt data in raw byte[] form. You can also construct TextEncryptors to encrypt text strings. Encryptors are thread-safe.

35.2.1 BytesEncryptor

Use the Encryptors.standard factory method to construct a "standard" BytesEncryptor:

Encryptors.standard("password", "salt");

The "standard" encryption method is 256-bit AES using PKCS #5’s PBKDF2 (Password-Based Key Derivation Function #2). This method requires Java 6. The password used to generate the SecretKey should be kept in a secure place and not be shared. The salt is used to prevent dictionary attacks against the key in the event your encrypted data is compromised. A 16-byte random initialization vector is also applied so each encrypted message is unique.

The provided salt should be in hex-encoded String form, be random, and be at least 8 bytes in length. Such a salt may be generated using a KeyGenerator:

String salt = KeyGenerators.string().generateKey(); // generates a random 8-byte salt that is then hex-encoded

35.2.2 TextEncryptor

Use the Encryptors.text factory method to construct a standard TextEncryptor:

Encryptors.text("password", "salt");

A TextEncryptor uses a standard BytesEncryptor to encrypt text data. Encrypted results are returned as hex-encoded strings for easy storage on the filesystem or in the database.

Use the Encryptors.queryableText factory method to construct a "queryable" TextEncryptor:

Encryptors.queryableText("password", "salt");

The difference between a queryable TextEncryptor and a standard TextEncryptor has to do with initialization vector (iv) handling. The iv used in a queryable TextEncryptor#encrypt operation is shared, or constant, and is not randomly generated. This means the same text encrypted multiple times will always produce the same encryption result. This is less secure, but necessary for encrypted data that needs to be queried against. An example of queryable encrypted text would be an OAuth apiKey.

35.3 Key Generators

The KeyGenerators class provides a number of convenience factory methods for constructing different types of key generators. Using this class, you can create a BytesKeyGenerator to generate byte[] keys. You can also construct a StringKeyGenerator to generate string keys. KeyGenerators are thread-safe.

35.3.1 BytesKeyGenerator

Use the KeyGenerators.secureRandom factory methods to generate a BytesKeyGenerator backed by a SecureRandom instance:

BytesKeyGenerator generator = KeyGenerators.secureRandom();
byte[] key = generator.generateKey();

The default key length is 8 bytes. There is also a KeyGenerators.secureRandom variant that provides control over the key length:

KeyGenerators.secureRandom(16);

Use the KeyGenerators.shared factory method to construct a BytesKeyGenerator that always returns the same key on every invocation:

KeyGenerators.shared(16);

35.3.2 StringKeyGenerator

Use the KeyGenerators.string factory method to construct a 8-byte, SecureRandom KeyGenerator that hex-encodes each key as a String:

KeyGenerators.string();

35.4 Password Encoding

The password package of the spring-security-crypto module provides support for encoding passwords. PasswordEncoder is the central service interface and has the following signature:

public interface PasswordEncoder {

String encode(String rawPassword);

boolean matches(String rawPassword, String encodedPassword);
}

The matches method returns true if the rawPassword, once encoded, equals the encodedPassword. This method is designed to support password-based authentication schemes.

The BCryptPasswordEncoder implementation uses the widely supported "bcrypt" algorithm to hash the passwords. Bcrypt uses a random 16 byte salt value and is a deliberately slow algorithm, in order to hinder password crackers. The amount of work it does can be tuned using the "strength" parameter which takes values from 4 to 31. The higher the value, the more work has to be done to calculate the hash. The default value is 10. You can change this value in your deployed system without affecting existing passwords, as the value is also stored in the encoded hash.

// Create an encoder with strength 16
BCryptPasswordEncoder encoder = new BCryptPasswordEncoder(16);
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));

The Pbkdf2PasswordEncoder implementation uses PBKDF2 algorithm to hash the passwords. In order to defeat password cracking PBKDF2 is a deliberately slow algorithm and should be tuned to take about .5 seconds to verify a password on your system.

// Create an encoder with all the defaults
Pbkdf2PasswordEncoder encoder = new Pbkdf2PasswordEncoder();
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));