passlib.hash.cisco_pix - Cisco PIX hash

New in version 1.6.

Warning

This hash is not secure, and should not be used for any purposes besides manipulating existing Cisco PIX password hashes.

This class implements the password hash algorithm commonly found on Cisco PIX firewalls. This class can be used directly as follows:

>>> from passlib.hash import cisco_pix as pix

>>> # encrypt password using specified username
>>> hash = pix.encrypt("password", user="user")
>>> hash
'A5XOy94YKDPXCo7U'

>>> # verify correct password
>>> pix.verify("password", hash, user="user")
True
>>> # verify correct password w/ wrong username
>>> pm.verify("password", hash, user="other")
False
>>> # verify incorrect password
>>> pm.verify("letmein", hash, user="user")
False

>>> # encrypt password without associate user account
>>> hash2 = pix.encrypt("password")
>>> hash2
'NuLKvvWGg.x9HEKO'

>>> # verify password without associated user account
>>> pix.verify("password", hash2)
True

See also

the generic PasswordHash usage examples

Interface

class passlib.hash.cisco_pix

This class implements the password hash used by Cisco PIX firewalls, and follows the Password Hash Interface. It does a single round of hashing, and relies on the username as the salt.

The encrypt(), genhash(), and verify() methods have the following extra keyword:

Parameters:user (str) –

String containing name of user account this password is associated with.

This is required in order to correctly hash passwords associated with a user account on the Cisco device, as it is used to salt the hash.

Conversely, this must be omitted or set to "" in order to correctly hash passwords which don’t have an associated user account (such as the “enable” password).

Note

This hash algorithm has a context-sensitive percularity. It takes in an optional username, used to salt the hash, but with specific restrictions...

• The username must be provided in order to correctly hash passwords associated with a user account on the Cisco device.
• Conversely, the username must not be provided (or must be set to "") in order to correctly hash passwords which don’t have an associated user account (such as the “enable” password).

Format & Algorithm

Cisco PIX hashes consist of a 12 byte digest, encoded as a 16 character HASH64-encoded string. An example hash (of "password") is "NuLKvvWGg.x9HEKO".

The digest is calculated as follows:

1. The password is encoded using an ASCII-compatible encoding (all known references are strict 7-bit ascii, and Passlib uses UTF-8 to provide unicode support).
2. If the hash is associated with a user account, append the first four bytes of the user account name to the end of the password. If the hash is NOT associated with a user account (e.g. it’s the “enable” password), this step should be omitted.
3. The resulting password should be truncated to 16 bytes, or the right side NULL padded to 16 bytes, as appropriate.
4. Run the result of step 3 through MD5.
5. Discard every 4th byte of the 16-byte MD5 hash, starting with the 4th byte.
6. Encode the 12-byte result using HASH64.

Security Issues

This algorithm is not suitable for any use besides manipulating existing Cisco PIX hashes, due to the following flaws:

• It’s use of the username as a salt value (and only the first four characters at that), means that common usernames (e.g. admin, cisco) will occur more frequently as salts, weakening the effectiveness of the salt in foiling pre-computed tables.
• It’s truncation of the password+user combination to 16 characters additionally limits the keyspace, and the effectiveness of the username as a salt; making pre-computed and brute force attacks much more feasible.
• Since the keyspace of user+password is still a subset of ascii characters, existing MD5 lookup tables have an increased chance of being able to reverse common hashes.
• It’s simplicity, and the weakness of MD5, makes high-speed brute force attacks much more feasible.
• Furthermore, it discards of 1/4 of MD5’s already small 16 byte digest, making collisions much more likely.

Deviations

This implementation differs from the standard in one main way:

• Unicode Policy:

  The official Cisco PIX algorithm is primarily used with ascii passwords, how it handles other characters is not known.

  In order to provide support for unicode strings, Passlib will encode unicode passwords using utf-8 before running them through this algorithm. If a different encoding is desired by an application, the password should be encoded before handing it to Passlib.

• While this implementation agrees with all known references, the actual algorithm has not been published by Cisco, so there may be other unknown deviations.

Footnotes

[1]	Description of PIX algorithm - http://www.perlmonks.org/index.pl?node_id=797623

[2]	Message threads hinting at how username is handled - http://www.openwall.com/lists/john-users/2010/02/02/7, www.freerainbowtables.com/phpBB3/viewtopic.php?f=2&t=1441