crypt
(PHP 4, PHP 5)
crypt — One-way string hashing
Description
$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.
The salt parameter is optional. However, crypt() creates weak password without salt. PHP 5.6 or later raise E_NOTICE error without it. Make sure specify strong enough salt for better security.
password_hash() uses strong hash, generates strong salt, applies proper rounds automatically. password_hash() is 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.
CautionUsing the
CRYPT_BLOWFISHalgorithm, will result in thestrparameter being truncated to a maximum length of 72 characters. This is only a concern if are using the same salt to hash strings with this algorithm that are over 72 bytes in length, as this will result in those hashes being identical. -
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.
Changelog
| Version | Description |
|---|---|
| 5.6.0 |
Raise E_NOTICE security warning if salt is omitted.
|
| 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. |
Examples
Example #1 crypt() examples
<?php
$hashed_password = crypt('mypassword'); // let the salt be automatically generated
/* You should pass the entire results of crypt() as the salt for comparing a
password, to avoid problems when different hashing algorithms are used. (As
it says above, standard DES-based password hashing uses a 2-character salt,
but MD5-based hashing uses 12.) */
if (crypt($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
Notes
Note: There is no decrypt function, since crypt() uses a one-way algorithm.
See Also
- password_hash() - Creates a password hash
- md5() - Calculate the md5 hash of a string
- The Mcrypt extension
- The Unix man page for your crypt function for more information
- addcslashes
- addslashes
- bin2hex
- chop
- chr
- chunk_split
- convert_cyr_string
- convert_uudecode
- convert_uuencode
- count_chars
- crc32
- crypt
- echo
- explode
- fprintf
- get_html_translation_table
- hebrev
- hebrevc
- hex2bin
- html_entity_decode
- htmlentities
- htmlspecialchars_decode
- htmlspecialchars
- implode
- join
- lcfirst
- levenshtein
- localeconv
- ltrim
- md5_file
- md5
- metaphone
- money_format
- nl_langinfo
- nl2br
- number_format
- ord
- parse_str
- printf
- quoted_printable_decode
- quoted_printable_encode
- quotemeta
- rtrim
- setlocale
- sha1_file
- sha1
- similar_text
- soundex
- sprintf
- sscanf
- str_getcsv
- str_ireplace
- str_pad
- str_repeat
- str_replace
- str_rot13
- str_shuffle
- str_split
- str_word_count
- strcasecmp
- strchr
- strcmp
- strcoll
- strcspn
- strip_tags
- stripcslashes
- stripos
- stripslashes
- stristr
- strlen
- strnatcasecmp
- strnatcmp
- strncasecmp
- strncmp
- strpbrk
- strpos
- strrchr
- strrev
- strripos
- strrpos
- strspn
- strstr
- strtok
- strtolower
- strtoupper
- strtr
- substr_compare
- substr_count
- substr_replace
- substr
- trim
- ucfirst
- ucwords
- vfprintf
- vprintf
- vsprintf
- wordwrap
Коментарии
Here is an expression to generate pseudorandom salt for the CRYPT_BLOWFISH hash type:
<?php $salt = substr(str_replace('+', '.', base64_encode(pack('N4', mt_rand(), mt_rand(), mt_rand(), mt_rand()))), 0, 22); ?>
It is intended for use on systems where mt_getrandmax() == 2147483647.
The salt created will be 128 bits in length, padded to 132 bits and then expressed in 22 base64 characters. (CRYPT_BLOWFISH only uses 128 bits for the salt, even though there are 132 bits in 22 base64 characters. If you examine the CRYPT_BLOWFISH input and output, you can see that it ignores the last four bits on input, and sets them to zero on output.)
Note that the high-order bits of the four 32-bit dwords returned by mt_rand() will always be zero (since mt_getrandmax == 2^31), so only 124 of the 128 bits will be pseudorandom. I found that acceptable for my application.
To generate salt use mcrypt_create_iv() not mt_rand() because no matter how many times you call mt_rand() it will only have at most 32 bits of entropy. Which you will start seeing salt collisions after about 2^16 users. mt_rand() is seeded poorly so it should happen sooner.
For bcrypt this will actually generate a 128 bit salt:
<?php $salt = strtr(base64_encode(mcrypt_create_iv(16, MCRYPT_DEV_URANDOM)), '+', '.'); ?>
*** Bike shed ***
The last character in the 22 character salt is 2 bits.
base64_encode() will have these four character "AQgw"
bcrypt will have these four character ".Oeu"
You don't need to do a full translate because they "round" to different characters:
echo crypt('', '$2y$05$.....................A') . "\n";
echo crypt('', '$2y$05$.....................Q') . "\n";
echo crypt('', '$2y$05$.....................g') . "\n";
echo crypt('', '$2y$05$.....................w') . "\n";
$2y$05$......................J2ihDv8vVf7QZ9BsaRrKyqs2tkn55Yq
$2y$05$.....................O/jw2XygQa2.LrIT7CFCBQowLowDP6Y.
$2y$05$.....................eDOx4wMcy7WU.kE21W6nJfdMimsBE3V6
$2y$05$.....................uMMcgjnOELIa6oydRivPkiMrBG8.aFp.
The crypt() function cant handle plus signs correctly. So if for example you are using crypt in a login function, use urlencode on the password first to make sure that the login procedure can handle any character:
<?php
$user_input = '12+#æ345';
$pass = urlencode($user_input));
$pass_crypt = crypt($pass);
if ($pass_crypt == crypt($pass, $pass_crypt)) {
echo "Success! Valid password";
} else {
echo "Invalid password";
}
?>
As I understand it, blowfish is generally seen a secure hashing algorithm, even for enterprise use (correct me if I'm wrong). Because of this, I created functions to create and check secure password hashes using this algorithm, and using the (also deemed cryptographically secure) openssl_random_pseudo_bytes function to generate the salt.
<?php
/*
* Generate a secure hash for a given password. The cost is passed
* to the blowfish algorithm. Check the PHP manual page for crypt to
* find more information about this setting.
*/
function generate_hash($password, $cost=11){
/* To generate the salt, first generate enough random bytes. Because
* base64 returns one character for each 6 bits, the we should generate
* at least 22*6/8=16.5 bytes, so we generate 17. Then we get the first
* 22 base64 characters
*/
$salt=substr(base64_encode(openssl_random_pseudo_bytes(17)),0,22);
/* As blowfish takes a salt with the alphabet ./A-Za-z0-9 we have to
* replace any '+' in the base64 string with '.'. We don't have to do
* anything about the '=', as this only occurs when the b64 string is
* padded, which is always after the first 22 characters.
*/
$salt=str_replace("+",".",$salt);
/* Next, create a string that will be passed to crypt, containing all
* of the settings, separated by dollar signs
*/
$param='$'.implode('$',array(
"2y", //select the most secure version of blowfish (>=PHP 5.3.7)
str_pad($cost,2,"0",STR_PAD_LEFT), //add the cost in two digits
$salt //add the salt
));
//now do the actual hashing
return crypt($password,$param);
}
/*
* Check the password against a hash generated by the generate_hash
* function.
*/
function validate_pw($password, $hash){
/* Regenerating the with an available hash as the options parameter should
* produce the same hash if the same password is passed.
*/
return crypt($password, $hash)==$hash;
}
?>
The #2 comment on this comments page (as of Feb 2015) is 9 years old and recommends phpass. I have independently security audited this product and, while it continues to be recommended for password security, it is actually insecure and should NOT be used. It hasn't seen any updates in years (still at v0.3) and there are more recent alternatives such as using the newer built-in PHP password_hash() function that are much better. Everyone, please take a few moments to confirm what I'm saying is accurate (i.e. review the phpass code for yourself) and then click the down arrow to sink the phpass comment to the bottom. You'll be increasing security across the Internet by doing so.
For those who want details: md5() with microtime() are a fallback position within the source code of phpass. Instead of terminating, it continues to execute code. The author's intentions of trying to work everywhere are admirable but, when it comes to application security, that stance actually backfires. The only correct answer in a security context is to terminate the application rather than fallback to a weak position that can potentially be exploited (usually by forcing that weaker position to happen).