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.
SEE ALSO¶
Authen::Passphrase, Crypt::PasswdMD5
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.
