Ubuntu Manpage: Authen::Passphrase::MD5Crypt - passphrases using the MD5-based Unix crypt()

Provided by: libauthen-passphrase-perl_0.008-3_all

NAME

       Authen::Passphrase::MD5Crypt - passphrases using the MD5-based Unix crypt()

SYNOPSIS

               use Authen::Passphrase::MD5Crypt;

               $ppr = Authen::Passphrase::MD5Crypt->new(
                               salt => "Vd3f8aG6",
                               hash_base64 => "GcsdF4YCXb0PM2UmXjIoI1");

               $ppr = Authen::Passphrase::MD5Crypt->new(
                               salt_random => 1,
                               passphrase => "passphrase");

               $ppr = Authen::Passphrase::MD5Crypt->from_crypt(
                       '$1$Vd3f8aG6$GcsdF4YCXb0PM2UmXjIoI1');

               $ppr = Authen::Passphrase::MD5Crypt->from_rfc2307(
                       '{CRYPT}$1$Vd3f8aG6$GcsdF4YCXb0PM2UmXjIoI1');

               $salt = $ppr->salt;
               $hash_base64 = $ppr->hash_base64;

               if($ppr->match($passphrase)) { ...

               $passwd = $ppr->as_crypt;
               $userPassword = $ppr->as_rfc2307;

DESCRIPTION

       An object of this class encapsulates a passphrase hashed using the MD5-based Unix crypt() hash function.
       This is a subclass of Authen::Passphrase, and this document assumes that the reader is familiar with the
       documentation for that class.

       The crypt() function in a modern Unix actually supports several different passphrase schemes.  This class
       is concerned only with one particular scheme, an MD5-based algorithm designed by Poul-Henning Kamp and
       originally implemented in FreeBSD.  To handle the whole range of passphrase schemes supported by the
       modern crypt(), see the from_crypt constructor and the as_crypt method in Authen::Passphrase.

       The MD5-based crypt() scheme uses the whole passphrase, a salt which can in principle be an arbitrary
       byte string, and the MD5 message digest algorithm.  First the passphrase and salt are hashed together,
       yielding an MD5 message digest.  Then a new digest is constructed, hashing together the passphrase, the
       salt, and the first digest, all in a rather complex form.  Then this digest is passed through a thousand
       iterations of a function which rehashes it together with the passphrase and salt in a manner that varies
       between rounds.  The output of the last of these rounds is the resulting passphrase hash.

       In the crypt() function the raw hash output is then represented in ASCII as a 22-character string using a
       base 64 encoding.  The base 64 digits are ".", "/", "0" to "9", "A" to "Z", "a" to "z" (in ASCII order).
       Because the base 64 encoding can represent 132 bits in 22 digits, more than the 128 required, the last
       digit can only take four of the base 64 digit values.  An additional complication is that the bytes of
       the raw algorithm output are permuted in a bizarre order before being represented in base 64.

       There is no tradition of handling these passphrase hashes in raw binary form.  The textual encoding
       described above, including the final permutation, is used universally, so this class does not support any
       binary format.

       The complex algorithm was designed to be slow to compute, in order to resist brute force attacks.
       However, the complexity is fixed, and the operation of Moore's Law has rendered it far less expensive
       than intended.  If efficiency of a brute force attack is a concern, see
       Authen::Passphrase::BlowfishCrypt.

CONSTRUCTORS

Authen::Passphrase::MD5Crypt->new(ATTR => VALUE, ...)
Generates a new passphrase recogniser object using the MD5-based crypt() algorithm. The following
attributes may be given:

salt
The salt, as a raw string. It may be any byte string, but in crypt() usage it is conventionally
limited to zero to eight base 64 digits.

salt_random
Causes salt to be generated randomly. The value given for this attribute is ignored. The salt
will be a string of eight base 64 digits. The source of randomness may be controlled by the
facility described in Data::Entropy.

hash_base64
The hash, as a string of 22 base 64 digits. This is the final part of what crypt() outputs.

passphrase
A passphrase that will be accepted.

The salt must be given, and either the hash or the passphrase.

Authen::Passphrase::MD5Crypt->from_crypt(PASSWD)
Generates a new passphrase recogniser object using the MD5-based crypt() algorithm, from a crypt
string. The crypt string must consist of "$1$", the salt, "$", then 22 base 64 digits giving the
hash. The salt may be up to 8 characters long, and cannot contain "$" or any character that cannot
appear in a crypt string.

Authen::Passphrase::MD5Crypt->from_rfc2307(USERPASSWORD)
Generates a new passphrase recogniser object using the MD5-based crypt() algorithm, from an RFC 2307
string. The string must consist of "{CRYPT}" (case insensitive) followed by an acceptable crypt
string.

METHODS

       $ppr->salt
           Returns the salt, in raw form.

       $ppr->hash_base64
           Returns the hash value, as a string of 22 base 64 digits.

       $ppr->match(PASSPHRASE)
       $ppr->as_crypt
       $ppr->as_rfc2307
           These methods are part of the standard Authen::Passphrase interface.  Not every passphrase recogniser
           of this type can be represented as a crypt string: the crypt format only allows the salt to be up  to
           eight bytes, and it cannot contain any NUL or "$" characters.

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2006, 2007, 2009, 2010, 2012 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This  module  is  free  software;  you  can redistribute it and/or modify it under the same terms as Perl
       itself.

perl v5.34.0                                       2022-06-08                  Authen::Passphrase::MD5Crypt(3pm)