crypt
— Function to check Unix passwords¶
Source code: Lib/crypt.py
Застаріло починаючи з версії 3.11: The crypt
module is deprecated
(see PEP 594 for details and alternatives).
The hashlib
module is a potential replacement for certain use cases.
This module implements an interface to the crypt(3) routine, which is a one-way hash function based upon a modified DES algorithm; see the Unix man page for further details. Possible uses include storing hashed passwords so you can check passwords without storing the actual password, or attempting to crack Unix passwords with a dictionary.
Notice that the behavior of this module depends on the actual implementation of the crypt(3) routine in the running system. Therefore, any extensions available on the current implementation will also be available on this module.
Availability: Unix. Not available on VxWorks.
Hashing Methods¶
Нове в версії 3.3.
The crypt
module defines the list of hashing methods (not all methods
are available on all platforms):
-
crypt.
METHOD_SHA512
¶ A Modular Crypt Format method with 16 character salt and 86 character hash based on the SHA-512 hash function. This is the strongest method.
-
crypt.
METHOD_SHA256
¶ Another Modular Crypt Format method with 16 character salt and 43 character hash based on the SHA-256 hash function.
-
crypt.
METHOD_BLOWFISH
¶ Another Modular Crypt Format method with 22 character salt and 31 character hash based on the Blowfish cipher.
Нове в версії 3.7.
-
crypt.
METHOD_MD5
¶ Another Modular Crypt Format method with 8 character salt and 22 character hash based on the MD5 hash function.
-
crypt.
METHOD_CRYPT
¶ The traditional method with a 2 character salt and 13 characters of hash. This is the weakest method.
Module Attributes¶
Нове в версії 3.3.
-
crypt.
methods
¶ A list of available password hashing algorithms, as
crypt.METHOD_*
objects. This list is sorted from strongest to weakest.
Module Functions¶
The crypt
module defines the following functions:
-
crypt.
crypt
(word, salt=None)¶ word will usually be a user’s password as typed at a prompt or in a graphical interface. The optional salt is either a string as returned from
mksalt()
, one of thecrypt.METHOD_*
values (though not all may be available on all platforms), or a full encrypted password including salt, as returned by this function. If salt is not provided, the strongest method available inmethods
will be used.Checking a password is usually done by passing the plain-text password as word and the full results of a previous
crypt()
call, which should be the same as the results of this call.salt (either a random 2 or 16 character string, possibly prefixed with
$digit$
to indicate the method) which will be used to perturb the encryption algorithm. The characters in salt must be in the set[./a-zA-Z0-9]
, with the exception of Modular Crypt Format which prefixes a$digit$
.Returns the hashed password as a string, which will be composed of characters from the same alphabet as the salt.
Since a few crypt(3) extensions allow different values, with different sizes in the salt, it is recommended to use the full crypted password as salt when checking for a password.
Змінено в версії 3.3: Accept
crypt.METHOD_*
values in addition to strings for salt.
-
crypt.
mksalt
(method=None, *, rounds=None)¶ Return a randomly generated salt of the specified method. If no method is given, the strongest method available in
methods
is used.The return value is a string suitable for passing as the salt argument to
crypt()
.rounds specifies the number of rounds for
METHOD_SHA256
,METHOD_SHA512
andMETHOD_BLOWFISH
. ForMETHOD_SHA256
andMETHOD_SHA512
it must be an integer between1000
and999_999_999
, the default is5000
. ForMETHOD_BLOWFISH
it must be a power of two between16
(24) and2_147_483_648
(231), the default is4096
(212).Нове в версії 3.3.
Змінено в версії 3.7: Added the rounds parameter.
Examples¶
A simple example illustrating typical use (a constant-time comparison
operation is needed to limit exposure to timing attacks.
hmac.compare_digest()
is suitable for this purpose):
import pwd
import crypt
import getpass
from hmac import compare_digest as compare_hash
def login():
username = input('Python login: ')
cryptedpasswd = pwd.getpwnam(username)[1]
if cryptedpasswd:
if cryptedpasswd == 'x' or cryptedpasswd == '*':
raise ValueError('no support for shadow passwords')
cleartext = getpass.getpass()
return compare_hash(crypt.crypt(cleartext, cryptedpasswd), cryptedpasswd)
else:
return True
To generate a hash of a password using the strongest available method and check it against the original:
import crypt
from hmac import compare_digest as compare_hash
hashed = crypt.crypt(plaintext)
if not compare_hash(hashed, crypt.crypt(plaintext, hashed)):
raise ValueError("hashed version doesn't validate against original")