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crypt
One-way string hashing
Description
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.
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.
Parameters
-
str
-
The string to be hashed.
Caution
Using the CRYPT_BLOWFISH algorithm, will result
in the str parameter being truncated to a
maximum length of 72 characters.
-
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.
Return Values
Returns the hashed string or a string that is shorter than 13 characters
and is guaranteed to differ from the salt on failure.
Warning
When validating passwords, a string comparison function that isn't
vulnerable to timing attacks should be used to compare the output of
crypt to the previously known hash. PHP 5.6 onwards
provides hash_equals for this purpose.
Examples
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";
}
?>
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
Notes
Note:
There is no decrypt function, since crypt uses a
one-way algorithm.
See Also
- hash_equals
- password_hash
- md5
- The Mcrypt extension
- The Unix man page for your crypt function for more information
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