crypt
One-way string hashing
WarningThis function
is not (yet) binary safe!
Description
string crypt(#[\SensitiveParameter]string $string, string $salt)
Prior to PHP 8.0.0, the salt parameter was optional. However, crypt creates a weak hash without the salt, and raises 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.
The hash type is triggered by the salt argument.
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 string, so longer strings
that start with the same eight characters will generate the same result
(when the same salt is used).
The following hash types are supported:
-
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 characters of iteration count
and 4 characters of salt. Each of these 4-character strings encode 24 bits, 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 algorithm and must be
in range 04-31, values outside this range will cause crypt() to fail.
"$2x$" hashes are potentially weak; "$2a$" hashes are compatible and
mitigate this weakness. For new hashes, "$2y$" should be used.
-
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.
Parameters
-
string
-
The string to be hashed.
Caution
Using the CRYPT_BLOWFISH algorithm, will result
in the string parameter being truncated to a
maximum length of 72 bytes.
-
salt
-
A 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
provides hash_equals for this purpose.
Examples
Example #1 crypt examples
<?php
$user_input = 'rasmuslerdorf';
$hashed_password = '$6$rounds=1000000$NJy4rIPjpOaU$0ACEYGg/aKCY3v8O8AfyiO7CTfZQ8/W231Qfh2tRLmfdvFD6XfHk12u6hMr9cYIA4hnpjLNSTRtUwYr9km9Ij/';
// Validate an existing crypt() hash in a way that is compatible with non-PHP software.
if (hash_equals($hashed_password, crypt($user_input, $hashed_password))) {
echo "Password verified!";
}
?>
Notes
Note:
There is no decrypt function, since crypt uses a
one-way algorithm.
See Also
- hash_equals
- password_hash
- The Unix man page for your crypt function for more information