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Manual Reference Pages  -  CRYPT::UNIXCRYPT_XS (3)

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Crypt::UnixCrypt_XS - perl xs interface for a portable traditional crypt function.



  use Crypt::UnixCrypt_XS qw/crypt/;
  my $hashed = crypt( $password, $salt );

  use Crypt::UnixCrypt_XS qw/crypt_rounds fold_password
      base64_to_block block_to_base64
      base64_to_int24 int24_to_base64
      base64_to_int12 int12_to_base64/;
  $block = crypt_rounds( $password, $nrounds, $saltnum, $block );
  $password = fold_password( $password );
  $block = base64_to_block( $base64 );
  $base64 = block_to_base64( $block );
  $saltnum = base64_to_int24( $base64 );
  $base64 = int24_to_base64( $saltnum );
  $saltnum = base64_to_int12( $base64 );
  $base64 = int12_to_base64( $saltnum );


This module implements the DES-based Unix crypt function. For those who need to construct non-standard variants of crypt, the various building blocks used in crypt are also supplied separately.


crypt( PASSWORD, SALT ) This is the conventional crypt interface. PASSWORD and SALT are both strings. The password will be hashed, in a manner determined by the salt, and a string is returned containing the salt and hash. The salt is at the beginning of the returned string, and only the beginning of the salt string is examined, so it is acceptable to use a string returned by crypt as a salt argument. Three different types of hashing may occur:

If the salt is an empty string, then the password is ignored and an empty string is returned. The empty salt/hash string is thus used to not require a password.

If the salt string starts with two base 64 digits (from the set [./0-9A-Za-z]), then the password is hashed using the traditional DES-based algorithm. The salt is used to modify the DES algorithm in one of 4096 different ways. The first eight characters of the password are used as a DES key, to encrypt a block of zeroes through 25 iterations of the modified DES. The block output by the final iteration is the hash, and it is returned in base 64 (as eleven digits).

If the salt string starts with an underscore character and then eight base 64 digits then the password is hashed using the extended DES-based algorithm from BSDi. The first four base 64 digits specify how many encryption rounds are to be performed. The next four base 64 digits are used to modify the DES algorithm in one of 16777216 different ways. If the password is longer than eight characters, it is hashed down to eight characters before being used as a key, so all characters of the password are significant.

crypt_rounds( PASSWORD, NROUNDS, SALTNUM, BLOCK ) This is the core of the DES-based crypt algorithm, exposed here to allow variant hash functions to be built. PASSWORD is a string; its first eight characters are used as a DES key. SALTNUM is an integer; its low 24 bits are used to modify the DES algorithm. BLOCK must be a string exactly eight bytes long. The data block is passed through NROUNDS iterations of the modified DES, and the final output block (also a string of exactly eight bytes) is returned.
fold_password( PASSWORD ) This is the pre-hashing algorithm used in the extended DES algorithm to fold a long password to the size of a DES key. It takes a password of any length, and returns a password of eight characters which is completely equivalent in the extended DES algorithm. Note: the password returned may contain NUL characters. The functions in this module correctly handle NULs in password strings, but a normal C library crypt cannot. If you need the short password to contain no NULs, perform the substitution s/\0/\x80/g: the top bit of each password character is ignored, so the result is equivalent.
base64_to_block( BASE64 ) This converts a data block from a string of eleven base 64 digits to a raw string of eight bytes.
block_to_base64( BLOCK ) This converts a data block from a raw string of eight bytes to a string of eleven base 64 digits.
base64_to_int24( BASE64 ) This converts a 24-bit integer from a string of four base 64 digits to a Perl integer.
int24_to_base64( VALUE ) This converts a 24-bit integer from a Perl integer to a string of four base 64 digits.
base64_to_int12( BASE64 ) This converts a 12-bit integer from a string of two base 64 digits to a Perl integer.
int12_to_base64( VALUE ) This converts a 12-bit integer from a Perl integer to a string of two base 64 digits.


None by default.


Crypt::UnixCrypt_XS provide a fast portable crypt function. Perl’s internal crypt is not present at every system. Perl calls the crypt function of the system’s C library. This may lead to trouble if the system’s crypt presents different results for the same key and salt, but different processid’s. Crypt::UnixCrypt is the cure here, but it is to slow. On my computer Crypt::UnixCrypt_XS is about 800 times faster than Crypt::UnixCrypt.


crypt(3), Crypt::UnixCrypt


Boris Zentner, <>, the original C source code was written by Eric Young,


Fixes, Bug Reports, Docs have been generously provided by:

  Andrew Main (Zefram) <>
  Guenter Knauf


Copyright (C) 2004, 2005, 2006, 2007 by Boris Zentner

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.3 or, at your option, any later version of Perl 5 you may have available.

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perl v5.20.3 CRYPT::UNIXCRYPT_XS (3) 2014-01-11

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