Zend\Crypt

Password

In the Zend\Crypt\Password namespace you can find all the password formats supported by Zend Framework. We currently support the following passwords:

  • bcrypt;
  • Apache (htpasswd).

If you need to choose a password format to store the user’s password we suggest to use the bcrypt algorithm that is considered secure against brute forcing attacks (see the details below).

Bcrypt

The bcrypt algorithm is an hashing algorithm that is widely used and suggested by the security community to store user’s passwords in a secure way.

Classic hashing mechanisms like MD5 or SHA, with or without a salt value, are not considered secure anymore (read this post to know why).

The security of bcrypt is related to the speed of the algorithm. Bcrypt is very slow, it can request even a second to generate an hash value. That means a brute force attack is impossible to execute, due to the amount of time that its need.

Bcrypt uses a cost parameter that specify the number of cycles to use in the algorithm. Increasing this number the algorithm will spend more time to generate the hash output. The cost parameter is represented by an integer value between 4 to 31. The default cost value of the Zend\Crypt\Password\Bcrypt component is 10, that means about 0.07 second using a CPU Intel i5 at 3.3Ghz (the cost parameter is a relative value according to the speed of the CPU used). We changed the default value of the cost parameter from 14 to 10, starting from Zend Framework 2.3.0, due to high computational time to prevent potential denial-of-service attacks (you can read this article Aggressive password stretching for more information).

If you want to change the cost parameter of the bcrypt algorithm you can use the setCost() method. Please note, if you change the cost parameter, the resulting hash will be different. This will not affect the verification process of the algorithm, therefore not breaking the password hashes you already have stored. Bcrypt reads the cost parameter from the hash value, during the password authentication. All of the parts needed to verify the hash are all together, separated with $’s, first the algorithm, then the cost, the salt, and then finally the hash.

The example below shows how to use the bcrypt algorithm to store a user’s password:

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use Zend\Crypt\Password\Bcrypt;

$bcrypt = new Bcrypt();
$securePass = $bcrypt->create('user password');

The output of the create() method is the hash of the password. This value can then be stored in a repository like a database (the output is a string of 60 bytes).

To verify if a given password is valid against a bcrypt value you can use the verify() method. An example is reported below:

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use Zend\Crypt\Password\Bcrypt;

$bcrypt = new Bcrypt();
$securePass = 'the stored bcrypt value';
$password = 'the password to check';

if ($bcrypt->verify($password, $securePass)) {
    echo "The password is correct! \n";
} else {
    echo "The password is NOT correct.\n";
}

In the bcrypt uses also a salt value to improve the randomness of the algorithm. By default, the Zend\Crypt\Password\Bcrypt component generates a random salt for each hash. If you want to specify a preselected salt you can use the setSalt() method.

We provide also a getSalt() method to retrieve the salt specified by the user. The salt and the cost parameter can be also specified during the constructor of the class, below is reported an example:

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use Zend\Crypt\Password\Bcrypt;

$bcrypt = new Bcrypt(array(
    'salt' => 'random value',
    'cost' => 11
));

Note

Bcrypt with non-ASCII passwords (8-bit characters)

The bcrypt implementation used by PHP < 5.3.7 can contains a security flaw if the password uses 8-bit characters (here’s the security report). The impact of this bug was that most (but not all) passwords containing non-ASCII characters with the 8th bit set were hashed incorrectly, resulting in password hashes incompatible with those of OpenBSD’s original implementation of bcrypt. This security flaw has been fixed starting from PHP 5.3.7 and the prefix used in the output was changed to ‘$2y$’ in order to put evidence on the correctness of the hash value. If you are using PHP < 5.3.7 with 8-bit passwords, the Zend\Crypt\Password\Bcrypt throws an exception suggesting to upgrade to PHP 5.3.7+ or use only 7-bit passwords.

Apache

The Zend\Crypt\Password\Apache supports all the password formats used by Apache (htpasswd). These formats are:

  • CRYPT, uses the traditional Unix crypt(3) function with a randomly-generated 32-bit salt (only 12 bits used) and the first 8 characters of the password;
  • SHA1, “{SHA}” + Base64-encoded SHA-1 digest of the password;
  • MD5, “$apr1$” + the result of an Apache-specific algorithm using an iterated (1,000 times) MD5 digest of various combinations of a random 32-bit salt and the password.
  • Digest, the MD5 hash of the string user:realm:password as a 32-character string of hexadecimal digits. realm is the Authorization Realm argument to the AuthName directive in httpd.conf.

In order to specify the format of the Apache’s password you can use the setFormat() method. An example with all the formats usage is reported below:

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use Zend\Crypt\Password\Apache;

$apache = new Apache();

$apache->setFormat('crypt');
printf ("CRYPT output: %s\n", $apache->create('password'));

$apache->setFormat('sha1');
printf ("SHA1 output: %s\n", $apache->create('password'));

$apache->setFormat('md5');
printf ("MD5 output: %s\n", $apache->create('password'));

$apache->setFormat('digest');
$apache->setUserName('enrico');
$apache->setAuthName('test');
printf ("Digest output: %s\n", $apache->create('password'));

You can also specify the format of the password during the constructor of the class:

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use Zend\Crypt\Password\Apache;

$apache = new Apache(array(
    'format' => 'md5'
));

Other possible parameters to pass in the constructor are username and authname, for the digest format.

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