PHP crypt() Function

crypt() will return a hashed string using the standard Unix DES-based algorithm or alternative algorithms that may be available on the system.

string crypt ( string $str [, string $salt ] )

The salt parameter is optional. However, crypt() creates a weak hash without the salt. PHP 5.6 or later raise an E_NOTICE error without it. Make sure to specify a strong enough salt for better security.

password_hash() uses a strong hash, generates a strong salt, and applies proper rounds automatically. password_hash() is a simple crypt() wrapper and compatible with existing password hashes. Use of password_hash() is encouraged.

There are some constants that are used together with the crypt() function. The value of these constants are set by PHP when it is installed.

Constants:

CRYPT_STD_DES - Standard DES-based hash with a two character salt from the alphabet "./0-9A-Za-z". Using invalid characters in the salt will cause crypt() to fail.

CRYPT_EXT_DES - Extended DES-based hash. The "salt" is a 9-character string consisting of an underscore followed by 4 bytes of iteration count and 4 bytes of salt. These are encoded as printable characters, 6 bits per character, least significant character first. The values 0 to 63 are encoded as "./0-9A-Za-z". Using invalid characters in the salt will cause crypt() to fail.

CRYPT_MD5 - MD5 hashing with a twelve character salt starting with $1$

CRYPT_BLOWFISH - Blowfish hashing with a salt as follows: "$2a$", "$2x$" or "$2y$", a two digit cost parameter, "$", and 22 characters from the alphabet "./0-9A-Za-z". Using characters outside of this range in the salt will cause crypt() to return a zero-length string. The two digit cost parameter is the base-2 logarithm of the iteration count for the underlying Blowfish-based hashing algorithmeter and must be in range 04-31, values outside this range will cause crypt() to fail. Versions of PHP before 5.3.7 only support "$2a$" as the salt prefix: PHP 5.3.7 introduced the new prefixes to fix a security weakness in the Blowfish implementation. Please refer to » this document for full details of the security fix, but to summarise, developers targeting only PHP 5.3.7 and later should use "$2y$" in preference to "$2a$".

CRYPT_SHA512 - SHA-512 hash with a sixteen character salt prefixed with $6$. If the salt string starts with 'rounds=$', the numeric value of N is used to indicate how many times the hashing loop should be executed, much like the cost parameter on Blowfish. The default number of rounds is 5000, there is a minimum of 1000 and a maximum of 999,999,999. Any selection of N outside this range will be truncated to the nearest limit.

Example -

Example #1 crypt() examples

<?php $hashed_password = crypt('mypassword'); // let the salt be automatically generated /* You should pass the entire results of crypt() as the salt for comparing a password, to avoid problems when different hashing algorithms are used. (As it says above, standard DES-based password hashing uses a 2-character salt, but MD5-based hashing uses 12.) */ if (hash_equals($hashed_password, crypt($user_input, $hashed_password))) { echo "Password verified!"; } ?>

Example #2 Using crypt() with htpasswd

<?php // Set the password $password = 'mypassword'; // Get the hash, letting the salt be automatically generated $hash = crypt($password); ?>

Example #3 Using crypt() with different hash types

<?php /* These salts are examples only, and should not be used verbatim in your code. You should generate a distinct, correctly-formatted salt for each password. */ if (CRYPT_STD_DES == 1) { echo 'Standard DES: ' . crypt('rasmuslerdorf', 'rl') . "\n"; } if (CRYPT_EXT_DES == 1) { echo 'Extended DES: ' . crypt('rasmuslerdorf', '_J9..rasm') . "\n"; } if (CRYPT_MD5 == 1) { echo 'MD5: ' . crypt('rasmuslerdorf', '$1$rasmusle$') . "\n"; } if (CRYPT_BLOWFISH == 1) { echo 'Blowfish: ' . crypt('rasmuslerdorf', '$2a$07$usesomesillystringforsalt$') . "\n"; } if (CRYPT_SHA256 == 1) { echo 'SHA-256: ' . crypt('rasmuslerdorf', '$5$rounds=5000$usesomesillystringforsalt$') . "\n"; } if (CRYPT_SHA512 == 1) { echo 'SHA-512: ' . crypt('rasmuslerdorf', '$6$rounds=5000$usesomesillystringforsalt$') . "\n"; } ?>

Run Example

Parameter	Description
str	The string to be hashed.
salt	An optional salt string to base the hashing on. If not provided, the behaviour is defined by the algorithm implementation and can lead to unexpected results.

Returns the hashed string or a string that is shorter than 13 characters and is guaranteed to differ from the salt on failure.