Authen::Passphrase.3pm

Langue: en

Autres versions - même langue

Version: 2007-01-21 (ubuntu - 07/07/09)

Section: 3 (Bibliothèques de fonctions)

NAME

Authen::Passphrase - hashed passwords/passphrases as objects

SYNOPSIS

         use Authen::Passphrase;
 
         $ppr = Authen::Passphrase->from_crypt($passwd);
         $ppr = Authen::Passphrase->from_rfc2307($userPassword);
 
         if($ppr->match($passphrase)) { ...
 
         $passphrase = $ppr->passphrase;
 
         $crypt = $ppr->as_crypt;
         $userPassword = $ppr->as_rfc2307;
 
 

DESCRIPTION

This is the base class for a system of objects that encapsulate passphrases. An object of this type is a passphrase recogniser: its job is to recognise whether an offered passphrase is the right one. For security, such passphrase recognisers usually do not themselves know the passphrase they are looking for; they can merely recognise it when they see it. There are many schemes in use to achieve this effect, and the intent of this class is to provide a consistent interface to them all, hiding the details.

The CPAN package Authen::Passphrase contains implementations of several specific passphrase schemes in addition to the base class.

PASSPHRASE ENCODINGS

Because hashed passphrases frequently need to be stored, various encodings of them have been devised. This class has constructors and methods to support these.

crypt encoding

The Unix crypt() function, which performs passphrase hashing, returns hashes in a textual format intended to be stored in a text file. In particular, such hashes are stored in /etc/passwd (and now /etc/shadow) to control access to Unix user accounts. The same textual format has been adopted and extended by other passphrase-handling software such as password crackers.

For historical reasons, there are several different syntaxes used in this format. The original DES-based password scheme represents its hashes simply as a string of thirteen base 64 digits. An extended variant of this scheme uses nineteen base 64 digits, preceded by an "_`` marker. A more general syntax was developed later, which starts the string with ''$``, an alphanumeric scheme identifier, and another ''$".

In addition to actual passphrase hashes, the crypt format can also represent a couple of special cases. The empty string indicates that there is no access control; it is possible to login without giving a passphrase. Finally, any string that is not a possible output of crypt() may be used to prevent login completely; "*" is the usual choice, but other strings are used too.

crypt strings are intended to be used in text files that use colon and newline characters as delimiters. This module treats the crypt string syntax as being limited to ASCII graphic characters excluding colon.

RFC 2307 encoding

RFC 2307 describes an encoding system for passphrase hashes, to be used in the "userPassword`` attribute in LDAP databases. It encodes hashes as ASCII text, and supports several passphrase schemes in an extensible way by starting the encoding with an alphanumeric scheme identifier enclosed in braces. There are several standard scheme identifiers. The ''{CRYPT}" scheme allows the use of any crypt encoding.

This module treats the RFC 2307 string syntax as being limited to ASCII graphic characters.

The RFC 2307 encoding is a good one, and is recommended for storage and exchange of passphrase hashes.

CONSTRUCTORS

Authen::Passphrase->from_crypt(PASSWD)
Returns a passphrase recogniser object matching the supplied crypt encoding. This constructor may only be called on the base class, not any subclass.

The specific passphrase recogniser class is loaded at runtime, so successfully loading "Authen::Passphrase" does not guarantee that it will be possible to use a specific type of passphrase recogniser. If necessary, check separately for presence and loadability of the recogniser class.

Known scheme identifiers:

$1$
A baroque passphrase scheme based on MD5, designed by Poul-Henning Kamp and originally implemented in FreeBSD. See Authen::Passphrase::MD5Crypt.
$2$
$2a$
Two versions of a passphrase scheme based on Blowfish, designed by Niels Provos and David Mazieres for OpenBSD. See Authen::Passphrase::BlowfishCrypt.
$3$
The NT-Hash scheme, which stores the MD4 hash of the passphrase expressed in Unicode. See Authen::Passphrase::NTHash.
$IPB2$
Invision Power Board 2.x salted MD5
$K4$
Kerberos AFS DES
$LM$
Half of the Microsoft LAN Manager hash scheme. The two halves of a LAN Manager hash can be separated and manipulated independently; this represents such an isolated half. See Authen::Passphrase::LANManagerHalf.
$NT$
The NT-Hash scheme, which stores the MD4 hash of the passphrase expressed in Unicode. See Authen::Passphrase::NTHash.

The $3$ identifier refers to the same hash algorithm, but has a slightly different textual format (an extra "$").

$P$
Portable PHP password hash (phpass), based on MD5. See Authen::Passphrase::PHPass.
$VMS1$
$VMS2$
$VMS3$
Three variants of the Purdy polynomial system used in VMS. See Authen::Passphrase::VMSPurdy.
$af$
Kerberos v4 TGT
$apr1$
A variant of the $1$ scheme, used by Apache.
$krb5$
Kerberos v5 TGT

The historical formats supported are:
"bbbbbbbbbbbbb"
("b" represents a base 64 digit.) The original DES-based Unix password hash scheme. See Authen::Passphrase::DESCrypt.
"_bbbbbbbbbbbbbbbbbbb"
("b" represents a base 64 digit.) Extended DES-based passphrase hash scheme from BSDi. See Authen::Passphrase::DESCrypt.
""
Accept any passphrase. See Authen::Passphrase::AcceptAll.
"*"
To handle historical practice, anything non-empty but shorter than 13 characters and not starting with "$" is treated as deliberately rejecting all passphrases. (See Authen::Passphrase::RejectAll.) Anything 13 characters or longer, or starting with "$", that is not recognised as a hash is treated as an error.

There are also two different passphrase schemes that use a crypt string consisting of 24 base 64 digits. One is named ``bigcrypt'' and appears in HP-UX, Digital Unix, and OSF/1 (see Authen::Passphrase::BigCrypt). The other is named ``crypt16'' and appears in Ultrix and Tru64 (see Authen::Passphrase::Crypt16). These schemes conflict. Neither of them is accepted as a crypt string by this constructor; such strings are regarded as invalid encodings.
Authen::Passphrase->from_rfc2307(USERPASSWORD)
Returns a passphrase recogniser object matching the supplied RFC 2307 encoding. This constructor may only be called on the base class, not any subclass.

The specific passphrase recogniser class is loaded at runtime. See the note about this for the "from_crypt" constructor above.

Known scheme identifiers:

{CLEARTEXT}
Passphrase stored in cleartext. See Authen::Passphrase::Clear.
{CRYPT}
The scheme identifier is followed by a crypt string.
{CRYPT16}
Used ambiguously by Exim, to refer to either crypt16 (see Authen::Passphrase::Crypt16) or bigcrypt (see Authen::Passphrase::BigCrypt) depending on compilation options. This is a bug, resulting from a confusion between the two algorithms. This module does not support any meaning for this scheme identifier.
{K5KEY}
Not a real passphrase scheme, but a placeholder to indicate that a Kerberos key stored separately should be checked against. No data follows the scheme identifier.
{KERBEROS}
Not a real passphrase scheme, but a placeholder to indicate that Kerberos should be invoked to check against a user's passphrase. The scheme identifier is followed by the user's username, in the form "name@realm".
{LANM}
Synonym for {LANMAN}, used by CommuniGate Pro.
{LANMAN}
The Microsoft LAN Manager hash scheme. See Authen::Passphrase::LANManager.
{MD4}
The MD4 digest of the passphrase is stored. See Authen::Passphrase::SaltedDigest.
{MD5}
The MD5 digest of the passphrase is stored. See Authen::Passphrase::SaltedDigest.
{MSNT}
The NT-Hash scheme, which stores the MD4 hash of the passphrase expressed in Unicode. See Authen::Passphrase::NTHash.
{NS-MTA-MD5}
An MD5-based scheme used by Netscape Mail Server. See Authen::Passphrase::NetscapeMail.
{RMD160}
The RIPEMD-160 digest of the passphrase is stored. See Authen::Passphrase::SaltedDigest.
{SASL}
Not a real passphrase scheme, but a placeholder to indicate that SASL should be invoked to check against a user's passphrase. The scheme identifier is followed by the user's username.
{SHA}
The SHA-1 digest of the passphrase is stored. See Authen::Passphrase::SaltedDigest.
{SMD5}
The MD5 digest of the passphrase plus a salt is stored. See Authen::Passphrase::SaltedDigest.
{SSHA}
The SHA-1 digest of the passphrase plus a salt is stored. See Authen::Passphrase::SaltedDigest.
{UNIX}
Not a real passphrase scheme, but a placeholder to indicate that Unix mechanisms should be used to check against a Unix user's login passphrase. The scheme identifier is followed by the user's username.
{WM-CRY}
Synonym for {CRYPT}, used by CommuniGate Pro.

METHODS

$ppr->match(PASSPHRASE)
Checks whether the supplied passphrase is correct. Returns a boolean.
$ppr->passphrase
If a matching passphrase can be easily determined by the passphrase recogniser then this method will return it. This is only feasible for very weak passphrase schemes. The method "die"s if it is infeasible.
$ppr->as_crypt
Encodes the passphrase recogniser in crypt format and returns the encoded result. "die"s if the passphrase recogniser cannot be represented in this form.
$ppr->as_rfc2307
Encodes the passphrase recogniser in RFC 2307 format and returns the encoded result. "die"s if the passphrase recogniser cannot be represented in this form.

SUBCLASSING

This class is designed to be subclassed, and cannot be instantiated alone. Any subclass must implement the "match" method. That is the minimum required.

Subclasses should implement the "as_crypt" and "as_rfc2307" methods and the "from_crypt" and "from_rfc2307" constructors wherever appropriate, with the following exception. If a passphrase scheme has a crypt encoding but no native RFC 2307 encoding, so it can be RFC 2307 encoded only by using the "{CRYPT}" scheme, then "as_rfc2307" and "from_rfc2307" should not be implemented by the class. There is a default implementation of the "as_rfc2307" method that uses "{CRYPT}" and "as_crypt", and a default implementation of the "from_rfc2307" method that recognises "{CRYPT}" and passes the embedded crypt string to the "from_crypt" constructor.

Implementation of the "passphrase" method is entirely optional. It should be attempted only for schemes that are so ludicrously weak as to allow passphrases to be cracked reliably in a short time. Dictionary attacks are not appropriate implementations.

SEE ALSO

crypt(3), RFC 2307

AUTHOR

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

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