4.2 More about the spring security Crypto module

4.2.1 Using key generators

two main types of key generators: BytesKeyGenerator and StringKeyGenerator
the definition of the StringKeyGenerator contract in this code snippet:

public interface StringKeyGenerator {
     String generateKey();
}

how to obtain a StringKeyGenerator instance and how to use it to get a salt value:

StringKeyGenerator keyGenerator = KeyGenerators.string();
String salt = keyGenerator.generateKey();

BytesKeyGenerator is defined as follows:

public interface BytesKeyGenerator {
    int getKeyLength();
    byte[] generateKey();
}

A default ByteKeyGenerator generates keys of 8-byte length:

BytesKeyGenerator keyGenerator = KeyGenerators.secureRandom();
byte [] key = keyGenerator.generateKey();
int keyLength = keyGenerator.getKeyLength();

change the key generator generates keys of 8-byte length

BytesKeyGenerator keyGenerator = KeyGenerators.secureRandom(16);

an implementation that returns the same key value for each call of the same key generator. key1 and key2 have the same value

BytesKeyGenerator keyGenerator = KeyGenerators.shared(16);
byte [] key1 = keyGenerator.generateKey();
byte [] key2 = keyGenerator.generateKey();

4.2.2 Using encryptors for encryption and decryption operations

There are two types of encryptors defined by the SSCM: BytesEncryptor and TextEncryptor
the definition of the TextEncryptor

public interface TextEncryptor {
     String encrypt(String text);
     String decrypt(String encryptedText);
}

the definition of the BytesEncryptor

public interface BytesEncryptor {
     byte[] encrypt(byte[] byteArray);
     byte[] decrypt(byte[] encryptedByteArray);
}

what options we have to build and use an encryptor

String salt = KeyGenerators.string().generateKey();
String password = "secret";
String valueToEncrypt = "HELLO";
BytesEncryptor e = Encryptors.standard(password, salt);
byte [] encrypted = e.encrypt(valueToEncrypt.getBytes());
byte [] decrypted = e.decrypt(encrypted);

To build a stronger instance of the byte encryptor, you can call the Encryptors.stronger()

BytesEncryptor e = Encryptors.stronger(password, salt);

an example of using a TextEncryptor

String valueToEncrypt = "HELLO";
TextEncryptor e = Encryptors.noOpText();
String encrypted = e.encrypt(valueToEncrypt);

String salt = KeyGenerators.string().generateKey();
String password = "secret";
String valueToEncrypt = "HELLO";
TextEncryptor e = Encryptors.text(password, salt); 
String encrypted = e.encrypt(valueToEncrypt);
String decrypted = e.decrypt(encrypted);

In the following example, the value of the encrypted1 equals the value of the encrypted2:

String salt = KeyGenerators.string().generateKey();
String password = "secret";
String valueToEncrypt = "HELLO";
TextEncryptor e = Encryptors.queryableText(password, salt); 
String encrypted1 = e.encrypt(valueToEncrypt);
String encrypted2 = e.encrypt(valueToEncrypt);