(PHP 4, PHP 5)
crypt — One-way string hashing
$str
[, string $salt
] )crypt() will return a hashed string using the standard Unix DES-based algorithm or alternative algorithms that may be available on the system.
Some operating systems support more than one type of hash. In
fact, sometimes the standard DES-based algorithm is replaced by an
MD5-based algorithm. The hash type is triggered by the salt argument.
Prior to 5.3, PHP would determine the available algorithms at install-time
based on the system's crypt(). If no salt is provided, PHP will
auto-generate either a standard two character (DES) salt, or a twelve
character (MD5), depending on the availability of MD5 crypt(). PHP sets a
constant named CRYPT_SALT_LENGTH which indicates the
longest valid salt allowed by the available hashes.
The standard DES-based crypt() returns the
salt as the first two characters of the output. It also only uses the
first eight characters of str, so longer strings
that start with the same eight characters will generate the same result
(when the same salt is used).
On systems where the crypt() function supports multiple hash types, the following constants are set to 0 or 1 depending on whether the given type is available:
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_SHA256 - SHA-256 hash with a sixteen character salt
prefixed with $5$. If the salt string starts with 'rounds=<N>$', 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.
CRYPT_SHA512 - SHA-512 hash with a sixteen character salt
prefixed with $6$. If the salt string starts with 'rounds=<N>$', 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.
Note:
As of PHP 5.3.0, PHP contains its own implementation and will use that if the system lacks of support for one or more of the algorithms.
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.
| Version | Description |
|---|---|
| 5.3.7 | Added $2x$ and $2y$ Blowfish modes to deal with potential high-bit attacks. |
| 5.3.2 | Added SHA-256 and SHA-512 crypt based on Ulrich Drepper's » implementation. |
| 5.3.2 | Fixed Blowfish behaviour on invalid rounds to return "failure" string ("*0" or "*1"), instead of falling back to DES. |
| 5.3.0 | PHP now contains its own implementation for the MD5 crypt, Standard DES, Extended DES and the Blowfish algorithms and will use that if the system lacks of support for one or more of the algorithms. |
Example #1 crypt() examples
<?php
$hashed_password = crypt('mypassword'); // let the salt be automatically generated
/* You should pass the entire results of crypt() as the salt for comparing a
password, to avoid problems when different hashing algorithms are used. (As
it says above, standard DES-based password hashing uses a 2-character salt,
but MD5-based hashing uses 12.) */
if (crypt($user_input, $hashed_password) == $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";
}
?>
The above example will output something similar to:
Standard DES: rl.3StKT.4T8M Extended DES: _J9..rasmBYk8r9AiWNc MD5: $1$rasmusle$rISCgZzpwk3UhDidwXvin0 Blowfish: $2a$07$usesomesillystringfore2uDLvp1Ii2e./U9C8sBjqp8I90dH6hi SHA-256: $5$rounds=5000$usesomesillystri$KqJWpanXZHKq2BOB43TSaYhEWsQ1Lr5QNyPCDH/Tp.6 SHA-512: $6$rounds=5000$usesomesillystri$D4IrlXatmP7rx3P3InaxBeoomnAihCKRVQP22JZ6EY47Wc6BkroIuUUBOov1i.S5KPgErtP/EN5mcO.ChWQW21
Note: There is no decrypt function, since crypt() uses a one-way algorithm.