crypt
(PHP 4, PHP 5)
crypt — One-way string encryption (hashing)
Description
string crypt
( string $str
[, string $salt
] )
Some operating systems support more than one type of encryption. In
fact, sometimes the standard DES-based encryption is replaced by an
MD5-based encryption algorithm. The encryption type is triggered by the
salt argument. At install time, PHP determines the capabilities of the
crypt function and will accept salts for other encryption types. If no
salt is provided, PHP will auto-generate a standard two character salt by
default, unless the default encryption type on the system is MD5, in
which case a random MD5-compatible salt is generated. PHP sets a
constant named CRYPT_SALT_LENGTH which tells you
whether a regular two character salt applies to your system or the longer
twelve character salt is applicable.
The standard DES-based encryption 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
encryption types, the following constants are set to 0 or 1
depending on whether the given type is available:
-
CRYPT_STD_DES - Standard DES-based encryption with a two character salt
-
CRYPT_EXT_DES - Extended DES-based encryption with a nine character salt
-
CRYPT_MD5 - MD5 encryption with a twelve character salt starting with
$1$
-
CRYPT_BLOWFISH - Blowfish encryption with a sixteen character salt
starting with $2$ or $2a$
Parameters
-
str
-
The string to be encrypted.
-
salt
-
An optional salt string to base the encryption on. If not provided,
one will be randomly generated by PHP each time you call this function.
If you are using the supplied salt, you should be aware that the salt
is generated once. If you are calling this function repeatedly, this
may impact both appearance and security.
Return Values
Returns the encrypted string.
Examples
Example #1 crypt() examples
<?php
$password = crypt('mypassword'); // let the salt be automatically generated
/* You should pass the entire results of crypt() as the salt for comparing a
password, to avoid problems when different hashing algorithms are used. (As
it says above, standard DES-based password hashing uses a 2-character salt,
but MD5-based hashing uses 12.) */
if (crypt($user_input, $password) == $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 encryption types
<?php
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$07$rasmuslerd...........$') . "\n";
}
?>
The above example will output
something similar to:
Standard DES: rl.3StKT.4T8M
Extended DES: _J9..rasmBYk8r9AiWNc
MD5: $1$rasmusle$rISCgZzpwk3UhDidwXvin0
Blowfish: $2a$07$rasmuslerd............nIdrcHdxcUxWomQX9j6kvERCFjTg7Ra
Notes
Note:
There is no decrypt function, since crypt() uses a
one-way algorithm.
See Also
- md5()
- The Mcrypt extension
- The Unix man page for your crypt function for more information
