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author | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
commit | 116aa62bf54a39697e25f21d6cf6799f7faa1349 (patch) | |
tree | 8db5729518ed4ca88e26f1e26cc8695151ca3eb3 /Doc/library/hashlib.rst | |
parent | 739c01d47b9118d04e5722333f0e6b4d0c8bdd9e (diff) | |
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Move the 3k reST doc tree in place.
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diff --git a/Doc/library/hashlib.rst b/Doc/library/hashlib.rst new file mode 100644 index 0000000..f255554 --- /dev/null +++ b/Doc/library/hashlib.rst @@ -0,0 +1,121 @@ + +:mod:`hashlib` --- Secure hashes and message digests +==================================================== + +.. module:: hashlib + :synopsis: Secure hash and message digest algorithms. +.. moduleauthor:: Gregory P. Smith <greg@users.sourceforge.net> +.. sectionauthor:: Gregory P. Smith <greg@users.sourceforge.net> + + +.. versionadded:: 2.5 + +.. index:: + single: message digest, MD5 + single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512 + +This module implements a common interface to many different secure hash and +message digest algorithms. Included are the FIPS secure hash algorithms SHA1, +SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5 +algorithm (defined in Internet :rfc:`1321`). The terms secure hash and message +digest are interchangeable. Older algorithms were called message digests. The +modern term is secure hash. + +.. warning:: + + Some algorithms have known hash collision weaknesses, see the FAQ at the end. + +There is one constructor method named for each type of :dfn:`hash`. All return +a hash object with the same simple interface. For example: use :func:`sha1` to +create a SHA1 hash object. You can now feed this object with arbitrary strings +using the :meth:`update` method. At any point you can ask it for the +:dfn:`digest` of the concatenation of the strings fed to it so far using the +:meth:`digest` or :meth:`hexdigest` methods. + +.. index:: single: OpenSSL + +Constructors for hash algorithms that are always present in this module are +:func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and +:func:`sha512`. Additional algorithms may also be available depending upon the +OpenSSL library that Python uses on your platform. + +For example, to obtain the digest of the string ``'Nobody inspects the spammish +repetition'``:: + + >>> import hashlib + >>> m = hashlib.md5() + >>> m.update("Nobody inspects") + >>> m.update(" the spammish repetition") + >>> m.digest() + '\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9' + +More condensed:: + + >>> hashlib.sha224("Nobody inspects the spammish repetition").hexdigest() + 'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2' + +A generic :func:`new` constructor that takes the string name of the desired +algorithm as its first parameter also exists to allow access to the above listed +hashes as well as any other algorithms that your OpenSSL library may offer. The +named constructors are much faster than :func:`new` and should be preferred. + +Using :func:`new` with an algorithm provided by OpenSSL:: + + >>> h = hashlib.new('ripemd160') + >>> h.update("Nobody inspects the spammish repetition") + >>> h.hexdigest() + 'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc' + +The following values are provided as constant attributes of the hash objects +returned by the constructors: + + +.. data:: digest_size + + The size of the resulting digest in bytes. + +A hash object has the following methods: + + +.. method:: hash.update(arg) + + Update the hash object with the string *arg*. Repeated calls are equivalent to + a single call with the concatenation of all the arguments: ``m.update(a); + m.update(b)`` is equivalent to ``m.update(a+b)``. + + +.. method:: hash.digest() + + Return the digest of the strings passed to the :meth:`update` method so far. + This is a string of :attr:`digest_size` bytes which may contain non-ASCII + characters, including null bytes. + + +.. method:: hash.hexdigest() + + Like :meth:`digest` except the digest is returned as a string of double length, + containing only hexadecimal digits. This may be used to exchange the value + safely in email or other non-binary environments. + + +.. method:: hash.copy() + + Return a copy ("clone") of the hash object. This can be used to efficiently + compute the digests of strings that share a common initial substring. + + +.. seealso:: + + Module :mod:`hmac` + A module to generate message authentication codes using hashes. + + Module :mod:`base64` + Another way to encode binary hashes for non-binary environments. + + http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf + The FIPS 180-2 publication on Secure Hash Algorithms. + + http://www.cryptography.com/cnews/hash.html + Hash Collision FAQ with information on which algorithms have known issues and + what that means regarding their use. + |