2
:mod:`hashlib` --- Secure hashes and message digests
3
====================================================
6
:synopsis: Secure hash and message digest algorithms.
7
.. moduleauthor:: Gregory P. Smith <greg@krypto.org>
8
.. sectionauthor:: Gregory P. Smith <greg@krypto.org>
12
single: message digest, MD5
13
single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512
15
This module implements a common interface to many different secure hash and
16
message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
17
SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5
18
algorithm (defined in Internet :rfc:`1321`). The terms "secure hash" and
19
"message digest" are interchangeable. Older algorithms were called message
20
digests. The modern term is secure hash.
23
If you want the adler32 or crc32 hash functions they are available in
24
the :mod:`zlib` module.
28
Some algorithms have known hash collision weaknesses, see the FAQ at the end.
30
There is one constructor method named for each type of :dfn:`hash`. All return
31
a hash object with the same simple interface. For example: use :func:`sha1` to
32
create a SHA1 hash object. You can now feed this object with objects conforming
33
to the buffer interface (normally :class:`bytes` objects) using the
34
:meth:`update` method. At any point you can ask it for the :dfn:`digest` of the
35
concatenation of the data fed to it so far using the :meth:`digest` or
36
:meth:`hexdigest` methods.
40
For better multithreading performance, the Python GIL is released for
41
strings of more than 2047 bytes at object creation or on update.
45
Feeding string objects is to :meth:`update` is not supported, as hashes work
46
on bytes, not on characters.
48
.. index:: single: OpenSSL; (use in module hashlib)
50
Constructors for hash algorithms that are always present in this module are
51
:func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and
52
:func:`sha512`. Additional algorithms may also be available depending upon the
53
OpenSSL library that Python uses on your platform.
55
For example, to obtain the digest of the byte string ``b'Nobody inspects the
56
spammish repetition'``::
60
>>> m.update(b"Nobody inspects")
61
>>> m.update(b" the spammish repetition")
63
b'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
71
>>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest()
72
'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
74
A generic :func:`new` constructor that takes the string name of the desired
75
algorithm as its first parameter also exists to allow access to the above listed
76
hashes as well as any other algorithms that your OpenSSL library may offer. The
77
named constructors are much faster than :func:`new` and should be preferred.
79
Using :func:`new` with an algorithm provided by OpenSSL:
81
>>> h = hashlib.new('ripemd160')
82
>>> h.update(b"Nobody inspects the spammish repetition")
84
'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'
86
The following values are provided as constant attributes of the hash objects
87
returned by the constructors:
92
The size of the resulting hash in bytes.
96
The internal block size of the hash algorithm in bytes.
98
A hash object has the following methods:
101
.. method:: hash.update(arg)
103
Update the hash object with the object *arg*, which must be interpretable as
104
a buffer of bytes. Repeated calls are equivalent to a single call with the
105
concatenation of all the arguments: ``m.update(a); m.update(b)`` is
106
equivalent to ``m.update(a+b)``.
109
.. method:: hash.digest()
111
Return the digest of the data passed to the :meth:`update` method so far.
112
This is a bytes array of size :attr:`digest_size` which may contain bytes in
113
the whole range from 0 to 255.
116
.. method:: hash.hexdigest()
118
Like :meth:`digest` except the digest is returned as a string object of
119
double length, containing only hexadecimal digits. This may be used to
120
exchange the value safely in email or other non-binary environments.
123
.. method:: hash.copy()
125
Return a copy ("clone") of the hash object. This can be used to efficiently
126
compute the digests of data sharing a common initial substring.
132
A module to generate message authentication codes using hashes.
135
Another way to encode binary hashes for non-binary environments.
137
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
138
The FIPS 180-2 publication on Secure Hash Algorithms.
140
http://www.cryptography.com/cnews/hash.html
141
Hash Collision FAQ with information on which algorithms have known issues and
142
what that means regarding their use.