/Doc/library/hashlib.rst

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  1. :mod:`hashlib` --- Secure hashes and message digests
  2. ====================================================
  3. .. module:: hashlib
  4. :synopsis: Secure hash and message digest algorithms.
  5. .. moduleauthor:: Gregory P. Smith <greg@krypto.org>
  6. .. sectionauthor:: Gregory P. Smith <greg@krypto.org>
  7. .. versionadded:: 2.5
  8. .. index::
  9. single: message digest, MD5
  10. single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512
  11. This module implements a common interface to many different secure hash and
  12. message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
  13. SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5
  14. algorithm (defined in Internet :rfc:`1321`). The terms secure hash and message
  15. digest are interchangeable. Older algorithms were called message digests. The
  16. modern term is secure hash.
  17. .. note::
  18. If you want the adler32 or crc32 hash functions they are available in
  19. the :mod:`zlib` module.
  20. .. warning::
  21. Some algorithms have known hash collision weaknesses, see the FAQ at the end.
  22. There is one constructor method named for each type of :dfn:`hash`. All return
  23. a hash object with the same simple interface. For example: use :func:`sha1` to
  24. create a SHA1 hash object. You can now feed this object with arbitrary strings
  25. using the :meth:`update` method. At any point you can ask it for the
  26. :dfn:`digest` of the concatenation of the strings fed to it so far using the
  27. :meth:`digest` or :meth:`hexdigest` methods.
  28. .. index:: single: OpenSSL; (use in module hashlib)
  29. Constructors for hash algorithms that are always present in this module are
  30. :func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and
  31. :func:`sha512`. Additional algorithms may also be available depending upon the
  32. OpenSSL library that Python uses on your platform.
  33. For example, to obtain the digest of the string ``'Nobody inspects the spammish
  34. repetition'``:
  35. >>> import hashlib
  36. >>> m = hashlib.md5()
  37. >>> m.update("Nobody inspects")
  38. >>> m.update(" the spammish repetition")
  39. >>> m.digest()
  40. '\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
  41. >>> m.digest_size
  42. 16
  43. >>> m.block_size
  44. 64
  45. More condensed:
  46. >>> hashlib.sha224("Nobody inspects the spammish repetition").hexdigest()
  47. 'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
  48. A generic :func:`new` constructor that takes the string name of the desired
  49. algorithm as its first parameter also exists to allow access to the above listed
  50. hashes as well as any other algorithms that your OpenSSL library may offer. The
  51. named constructors are much faster than :func:`new` and should be preferred.
  52. Using :func:`new` with an algorithm provided by OpenSSL:
  53. >>> h = hashlib.new('ripemd160')
  54. >>> h.update("Nobody inspects the spammish repetition")
  55. >>> h.hexdigest()
  56. 'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'
  57. The following values are provided as constant attributes of the hash objects
  58. returned by the constructors:
  59. .. data:: digest_size
  60. The size of the resulting hash in bytes.
  61. .. data:: block_size
  62. The internal block size of the hash algorithm in bytes.
  63. A hash object has the following methods:
  64. .. method:: hash.update(arg)
  65. Update the hash object with the string *arg*. Repeated calls are equivalent to
  66. a single call with the concatenation of all the arguments: ``m.update(a);
  67. m.update(b)`` is equivalent to ``m.update(a+b)``.
  68. .. method:: hash.digest()
  69. Return the digest of the strings passed to the :meth:`update` method so far.
  70. This is a string of :attr:`digest_size` bytes which may contain non-ASCII
  71. characters, including null bytes.
  72. .. method:: hash.hexdigest()
  73. Like :meth:`digest` except the digest is returned as a string of double length,
  74. containing only hexadecimal digits. This may be used to exchange the value
  75. safely in email or other non-binary environments.
  76. .. method:: hash.copy()
  77. Return a copy ("clone") of the hash object. This can be used to efficiently
  78. compute the digests of strings that share a common initial substring.
  79. .. seealso::
  80. Module :mod:`hmac`
  81. A module to generate message authentication codes using hashes.
  82. Module :mod:`base64`
  83. Another way to encode binary hashes for non-binary environments.
  84. http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
  85. The FIPS 180-2 publication on Secure Hash Algorithms.
  86. http://www.cryptography.com/cnews/hash.html
  87. Hash Collision FAQ with information on which algorithms have known issues and
  88. what that means regarding their use.