crypt

Description

string crypt ( string str [, string salt] )

crypt() will return an encrypted string using the standard Unix DES-based encryption algorithm or alternative algorithms that may be available on the system. Arguments are a string to be encrypted and an optional salt string to base the encryption on. See the Unix man page for your crypt function for more information.

If the salt argument is not provided, one will be randomly generated by PHP each time you call this function.

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.

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.

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 $2a$

注: There is no decrypt function, since crypt() uses a one-way algorithm.

例子 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!";
}
?>

例子 2. Using crypt() with htpasswd


<?php
// Set the password
$password = 'mypassword';

// Get the hash, letting the salt be automatically generated
$hash = crypt($password);
?>

例子 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";
}
?>

上例的输出类似于：

Standard DES: rl.3StKT.4T8M
Extended DES: _J9..rasmBYk8r9AiWNc
MD5:          $1$rasmusle$rISCgZzpwk3UhDidwXvin0
Blowfish:     $2a$07$rasmuslerd............nIdrcHdxcUxWomQX9j6kvERCFjTg7Ra

See also md5() and the Mcrypt extension.

add a note User Contributed Notes

solar at openwall dot com
26-Oct-2006 05:17


The approach suggested in the note by Michael Stapelberg must not be used - it's an obvious security hole, leaking up to 12 bits of the plaintext password into the resulting string.

Michael Stapelberg
10-Oct-2006 03:30


In order to use crypt() for generating htpasswd-passwords I had to use it with base64_encode($password) as second paramter:



<?php

$hash = crypt($password, base64_encode($password));

?>

picolobo at pilab dot dyndns dot org
22-Sep-2006 04:49


I had problems with ENCRYPT MySQL function when i tried to compare with the encrypted password (with ENCRYPT).



Another solution i read from "UNIX Advanced programming" where i found about the UNIX system call "crypt()":



Password="tB" //The two first letters of encrypted password



SELECT password from users where Password=ENCRYPT('".$_POST['password']."',Password)



mysql> select password from users where password=encrypt('pasword','tB');

+---------------+

| password      |

+---------------+

| tBY8OVuabSiTU |

+---------------+

1 row in set (0.01 sec)



Bye.



> topace at lightbox dot org

> 22-Sep-2005 06:34

>

> To authenticate against a stored crypt in MySQL, simply use:

>

> SELECT ................

>           AND Password=ENCRYPT('".$_POST['password']."',Password)

solar at openwall dot com
24-Dec-2005 03:20


With different password hashing methods supported on different systems and with the need to generate salts with your own PHP code in order to use the more advanced / more secure methods, it takes special knowledge to use crypt() optimally, producing strong password hashes.  Other message digest / hashing functions supported by PHP, such as md5() and sha1(), are really no good for password hashing if used naively, resulting in hashes which may be brute-forced at rates much higher than those possible for hashes produced by crypt().



I have implemented a PHP password hashing framework (in PHP, tested with all of PHP 3, 4, and 5) which hides the complexity from your PHP applications (no need for you to worry about salts, etc.), yet does things in almost the best way possible given the constraints of the available functions.  The homepage for the framework is:



http://www.openwall.com/phpass/



I have placed this code in the public domain, so there are no copyrights or licensing restrictions to worry about.



P.S. I have 10 years of experience in password (in)security and I've developed several other password security tools and libraries.  So most people can feel confident they're getting this done better by using my framework than they could have done it on their own.

hotdog (at) gmx (dot) net
16-Nov-2005 11:34


WRONG:



$mypassword = "toto";

$smd5_pass = "{SMD5}......." // in openldap



if (preg_match ("/{SMD5}/i", $smd5_pass))

 {

  $encrypted = substr($md5_pass, 6);

  $hash = base64_decode($encrypted);

  $salt = substr($hash,16);

  $mhashed =  mhash(MHASH_MD5, $mypassword . $salt) ;

  $without_salt = explode($salt,$hash_hex);

   if ($without_salt[0] == $mhashed) {

    echo "Password verified <br>";

    } else {

    echo "Password Not verified<br>";

    }

 }



$without_salt = explode($salt,$hash_hex); should be $without_salt = explode($salt,$hash); 



RIGHT:



$mypassword = "toto";

$smd5_pass = "{SMD5}......." // in openldap



if (preg_match ("/{SMD5}/i", $smd5_pass))

 {

  $encrypted = substr($md5_pass, 6);

  $hash = base64_decode($encrypted);

  $salt = substr($hash,16);

  $mhashed =  mhash(MHASH_MD5, $mypassword . $salt) ;

  $without_salt = explode($salt,$hash);

   if ($without_salt[0] == $mhashed) {

    echo "Password verified <br>";

    } else {

    echo "Password Not verified<br>";

    }

 }

bjorninges dot spam at gmail dot com
07-Nov-2005 06:16


Note to topace's code: you should not use $_POST['password'] directly in your query as you are open to sql-injects.

Use the quote_smart() function from http://no.php.net/mysql_real_escape_string before adding user-submitted data to the query

topace at lightbox dot org
23-Sep-2005 12:34


To authenticate against a stored crypt in MySQL, simply use:



SELECT ................

            AND Password=ENCRYPT('".$_POST['password']."',Password)

MagicalTux at FF dot st
15-Jun-2005 03:53


Since many of you are wondering why when providing salt the characters over the 8th are ignored in the password, I'll clarify it a bit.



By default, PHP will try to use the best encryption method available on your system : MD5 or Simple DES.

Usually this is the MD5 method ($1$).

In this case, the salt must look like : "$1$xxxxxxxx$" where x are random ASCII characters. When you use MD5 passwords, all characters of the password are encrypted in this 34 characters hash.



However if your salt starts with an ASCII character, the system will assume it's a standard DES encrypted password. The main weakness of this system : only the 8 first characters of the password are used.



A correct version of the code :



<?php

function makesalt($type=CRYPT_SALT_LENGTH) {

  switch($type) {

    case 8:

      $saltlen=9; $saltprefix='$1$'; $saltsuffix='$'; break;

    case 2:

    default: // by default, fall back on Standard DES (should work everywhere)

      $saltlen=2; $saltprefix=''; $saltsuffix=''; break;

    #

  }

  $salt='';

  while(strlen($salt)<$saltlen) $salt.=chr(rand(64,126));

  return $saltprefix.$salt.$saltsuffix;

}



$salt=makesalt();

$longpassword='fez1c89ez1c98ez4c89z4eqf98ez';



$encrypted = crypt($longpassword, $salt);



$encrypted2 = crypt(substr($longpassword, 0, 8), $encrypted);



if ($encrypted == $encrypted2) {

  echo 'Match: Weak encryption method (Standard DES)';

} else {

  echo 'NoMatch: Strong encryption method (MD5)';

}

?>



If you use makesalt(2) you will force usage of Standard DES method, and the passwords will match. If you just use makesalt() there's great chances you'll have a MD5 password (don't know any system used nowadays which does not support MD5 passwords).



Finally, do not look at md5() PHP function if you want a md5 password, that's not related. UNIX MD5 passwords uses a salt, are 34 character long and start with $1$. The reply from md5() is 32 characters long, and is more adapted for file integrity check (call that a checksum).



Some people use sha1() passwords but without salt. Here's my simple sha1crypt function which will work with standard crypt passwords (by calling crypt()) AND a home-made "sha1" encryption method.



<?php

// NOTE: This function requires PHP 5.0.0 as we use "raw output" option of sha1()

function sha1crypt($password, $salt=null) {

  if ( (is_null($salt)) || (strlen($salt)<1) ) {

    $salt='';

    while(strlen($salt)<10) $salt.=chr(rand(64,126));

    $salt='$sha1$'.$salt.'$';

  }

  if ($salt{0}!='$') return crypt($password, $salt);

  $tmp=explode('$',$salt);

  if ($tmp[1]!='sha1') return crypt($password, $salt);

  $saltstr=$tmp[2];

  if (strlen($saltstr) != 10) return crypt($password, $salt);

  $encrypt=base64_encode(sha1($saltstr.$password,true));

  return '$sha1$'.$saltstr.'$'.$encrypt;

}



// without salt, sha1crypt() will generate on

$pass=sha1crypt('foobar');

echo $pass."\n";



// pass directly password as salt - different output as password is not the same

echo sha1crypt('foobarbaz',$pass)."\n";



// same password - same output

echo sha1crypt('foobar',$pass)."\n";



// Encrypt using MD5 passwords

echo sha1crypt('foobar','$1$blahblahg$')."\n";

?>



will output:

$sha1$oFkYeI|vuu$d3n7D30OnecZSbS6KIbxCch608A=

$sha1$oFkYeI|vuu$iA8KmbCZun1G1gEw2qVr42ELVH4=

$sha1$oFkYeI|vuu$d3n7D30OnecZSbS6KIbxCch608A=

$1$blahblah$/8Hme91aEkHzLaVk0g9EQ0



My sha1-encrypted passwords are 45 characters long.



Remember to read that too before using SHA1 passwords too :

http://www.schneier.com/blog/archives/2005/02/sha1_broken.html

ceo at l-i-e dot com
07-Jun-2005 09:03


The people confused about the first 2 characters of the plain-text password being used as the salt are... confused.



AFTER you crypt() your plain-text password, with 2 RANDOM characters, the RESULTING scrambled output with have the 2 randomly-selected characters as its first 2 characters.



Later, to check a password presented by the user, you use the first 2 characters of the SCRAMBLED password as the salt.



So you do not need to remember the salt elsewhere -- it is buried in the encrypted output.



This is by design by very very very clever cryptologists, and in no way, shape, or form decreases the "security" of the algorithm.



The same is true of all the encryption algorithms here -- The salt may be 27 characters long, and embedded in the middle of the crypted string, but it's still there, and that's Good.



I hope this note decreases the confusion caused by the 2 early notes discussing salt.

Vlad Alexa Mancini mancin at nextcode dot org
16-May-2005 04:57


cleaner version of shadow() and with more ascii chars



<?php



function shadow ($input){

         for ($n = 0; $n < 9; $n++){

              $s .= chr(rand(64,126));

         }

         $seed =  "$1$".$s."$";

         $return = crypt($input,$seed);

    return $return;

}



>

kevin at sylandroXgetridofthisbitX dot com
20-Apr-2005 03:55


Even worse, using the first two letters of the password as the salt removes the whole point of having salt in the first place, which is that without it, it's trivial to create a dictionary of passwords-to-encrypted-passwords.  Without salt (or with using a salt directly derived from the password) there's only one possible encrypted password per password.  With the two character salt, there's 4096, which makes the idea a lot less feasible.

19-Apr-2005 04:57


>icecube at fr dot fm 07-Mar-2002 09:53 

>To generate a .htaccess-based authentication with DES,

>you have to use the first two characters of your password

>as salt.



This is a _really_ bad idea, seeing how the two first letters of your password will be reveiled, effectively reducing the quality of your password.



Your example assigns "sonH/h2hpGtHk" to $ht_pass, where "so" of course are the first to letters in something. Try it out for yourself. Switching the password to "icecube" gives "ickJ.ZxzjXpNE" as the output. Get my point?



The salt is always included in the encrypted string. Use a random salt instead.

postal2600 at yahoo dot com
16-Mar-2005 06:07


I'll take the example from above and take a situation that I've ecountered and show you something that puts this function in a dark shadow of insecurity:



<?php

$password = crypt('postal2600','CyberBoard');



if (crypt('postal26??', $password) == $password) {

   echo "Password verified!";

}

?> 



Instad of ?? you can put anything an see that allway the password will be verified. So i strongly recomand that the md5 function should be used instead.

kb at -NOSPAM-diggersdive dot info
31-Dec-2004 12:18


It is likely that the php version of crypt() interfaces relatively directly with the C-library crypt() function, usually contained in libcrypt.  



Depending on your implementation and the default salt, you may or may not get the same crypt'd password out of eight characters as you would a longer string starting with those same eight characters.



See crypt(3) on your system for more documentation on how it works based on different encryption types.

genius at clan-aftershock dot com
29-Nov-2004 09:10


I discovered in the script stated before, when using a salt string the passwords length cannot be longer than 8 characters. However, when not using a salt string, it can exceded that limit.



Modified Example from athony, not using the salt.



<?php

$password = "qwertyuiopasdfghjkl";



// Not using any salts



$encrypted = crypt($password);



// Now do the comparison



$shortPass = substr($password, 0, 8);



if (crypt( $shortPass,  $encrypted ) == $encrypted )

   echo "The passwords match";

else

   echo "The passwords do not match";

?>



This will print: "The passwords do not match"



The check for password would still work if it was correct. Just by shortening the password string to eight, or extending the substr, or decalring the shortpass the same as the pass, it would be: "The passwords do match"



So the eight letter limit only works when using a salt.

antony at anonymous dot anon dot com
27-Nov-2004 12:21


There appears to be a limitation with this function, where it only validates upto a characters, therefore the 9th character onwards can be ommitted, which limits useful passwords to 8 characters only. Example



<?php

$password = "qwertyuiopasdfghjkl";



// Encrypt the password, but let's use a known MD5 hash as the salt



$salt = ""0f2d92cee71e5f93f3abecdc666a6b7d";

$salt = substr($salt, 0, CRYPT_SALT_LENGTH );



$encrypted = crypt($password, $salt);



// Now do the comparison



$shortPass = substr($password, 0, 8);



if (crypt( $shortPass,  $encrypted ) == $encrypted )

    echo "The passwords match";

else

    echo "The passwords do not match";

?>



This will print: "The passwords match" even though $shortPass is "qwertyui" and $password is "qwertyuiopasdfghjkl"

thorhajo at gmail dot com
03-Sep-2004 06:34


Here's a little function I wrote to generate MD5 password hashes in the format they're found in /etc/shadow:



function shadow($password)

{

  $hash = '';

  for($i=0;$i<8;$i++)

  {

    $j = mt_rand(0,53);

    if($j<26)$hash .= chr(rand(65,90));

    else if($j<52)$hash .= chr(rand(97,122));

    else if($j<53)$hash .= '.';

    else $hash .= '/';

  }

  return crypt($password,'$1$'.$hash.'$');

}



I've written this so that each character in the a-zA-Z./ set has a 1/54 of a chance of being selected (26 + 26 + 2 = 54), thus being statistically even.

aidan at php dot net
05-Jul-2004 10:52


Text_Password allows one to create pronounceable and unpronounceable passwords.



http://pear.php.net/package/text_password

php at SPAM_tlarson dot com
26-Jun-2002 01:17


There's always been a bit of confusion as to what makes a good salt and what doesn't.  Remember that it doesn't matter at all how easy a salt is to guess. No one ever HAS to guess the salt: it's already given.





The only only important consideration when generating a salt is to make sure that all salts are unique--that way the same password will be encrypted differently (i.e. the encrypted passwords will look different) for different users.





One of the simplest ways to generate a unique salt is to use some string that will be different every time the procedure is called.  Here's a simple example:





<?php


$jumble = md5(time() . getmypid());


$salt = substr($jumble,0,$salt_length);


?>





Given a string consisting of the current time (in seconds) concatinated with the current process id, the string will never be the same twice, assuming that the function is never called more than once per second.  Calculating the md5 sum over that string creates another string from which you can extract any substring and still end up with a unique sequence.





If you're going to be generating more than one password per second, just throw a rand($x,$y) in there to add a little more entropy.

add a note