Encrypt/decrypt using block ciphers

Zend\Crypt\BlockCipher implements the encrypt-then-authenticate mode using HMAC to provide authentication.

The symmetric cipher can be choose with a specific adapter that implements the Zend\Crypt\Symmetric\SymmetricInterface. We support the standard algorithms of the Mcrypt extension. The adapter that implements the Mcrypt is Zend\Crypt\Symmetric\Mcrypt.

In the following code we reported an example on how to use the BlockCipher class to encrypt-then-authenticate a string using the AES block cipher (with a key of 256 bit) and the HMAC algorithm (using the SHA-256 hash function).

use Zend\Crypt\BlockCipher;

$blockCipher = BlockCipher::factory('mcrypt', array('algo' => 'aes'));
$blockCipher->setKey('encryption key');
$result = $blockCipher->encrypt('this is a secret message');
echo "Encrypted text: $result \n";

The BlockCipher is initialized using a factory method with the name of the cipher adapter to use (mcrypt) and the parameters to pass to the adapter (the AES algorithm). In order to encrypt a string we need to specify an encryption key and we used the setKey() method for that scope. The encryption is provided by the encrypt() method.

The output of the encryption is a string, encoded in Base64 (default), that contains the HMAC value, the IV vector, and the encrypted text. The encryption mode used is the CBC (with a random IV by default) and SHA256 as default hash algorithm of the HMAC. The Mcrypt adapter encrypts using the PKCS#7 padding mechanism by default. You can specify a different padding method using a special adapter for that (Zend\Crypt\Symmetric\Padding). The encryption and authentication keys used by the BlockCipher are generated with the PBKDF2 algorithm, used as key derivation function from the user’s key specified using the setKey() method.

Note

Key size

BlockCipher try to use always the longest size of the key for the specified cipher. For instance, for the AES algorithm it uses 256 bits and for the Blowfish algorithm it uses 448 bits.

You can change all the default settings passing the values to the factory parameters. For instance, if you want to use the Blowfish algorithm, with the CFB mode and the SHA512 hash function for HMAC you have to initialize the class as follow:

use Zend\Crypt\BlockCipher;

$blockCipher = BlockCipher::factory('mcrypt', array(
                                'algo' => 'blowfish',
                                'mode' => 'cfb',
                                'hash' => 'sha512'
                            ));

Note

Recommendation

If you are not familiar with symmetric encryption techniques we strongly suggest to use the default values of the BlockCipher class. The default values are: AES algorithm, CBC mode, HMAC with SHA256, PKCS#7 padding.

To decrypt a string we can use the decrypt() method. In order to successfully decrypt a string we have to configure the BlockCipher with the same parameters of the encryption.

We can also initialize the BlockCipher manually without use the factory method. We can inject the symmetric cipher adapter directly to the constructor of the BlockCipher class. For instance, we can rewrite the previous example as follow:

use Zend\Crypt\BlockCipher;
use Zend\Crypt\Symmetric\Mcrypt;

$blockCipher = new BlockCipher(new Mcrypt(array('algo' => 'aes')));
$blockCipher->setKey('encryption key');
$result = $blockCipher->encrypt('this is a secret message');
echo "Encrypted text: $result \n";