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diff --git a/Doc/library/hashlib.rst b/Doc/library/hashlib.rst index d5531c4..3bf30bb 100644 --- a/Doc/library/hashlib.rst +++ b/Doc/library/hashlib.rst @@ -32,6 +32,10 @@ digests. The modern term is secure hash. Some algorithms have known hash collision weaknesses, refer to the "See also" section at the end. + +Hash algorithms +--------------- + 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 :term:`bytes-like @@ -174,6 +178,43 @@ A hash object has the following methods: compute the digests of data sharing a common initial substring. +Key Derivation Function +----------------------- + +Key derivation and key stretching algorithms are designed for secure password +hashing. Naive algorithms such as ``sha1(password)`` are not resistant +against brute-force attacks. A good password hashing function must be tunable, +slow and include a salt. + + +.. function:: pbkdf2_hmac(name, password, salt, rounds, dklen=None) + + The function provides PKCS#5 password-based key derivation function 2. It + uses HMAC as pseudorandom function. + + The string *name* is the desired name of the hash digest algorithm for + HMAC, e.g. 'sha1' or 'sha256'. *password* and *salt* are interpreted as + buffers of bytes. Applications and libraries should limit *password* to + a sensible value (e.g. 1024). *salt* should be about 16 or more bytes from + a proper source, e.g. :func:`os.urandom`. + + The number of *rounds* should be chosen based on the hash algorithm and + computing power. As of 2013 a value of at least 100,000 rounds of SHA-256 + have been suggested. + + *dklen* is the length of the derived key. If *dklen* is ``None`` then the + digest size of the hash algorithm *name* is used, e.g. 64 for SHA-512. + + >>> import hashlib, binascii + >>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000) + >>> binascii.hexlify(dk) + b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5' + + .. versionadded:: 3.4 + + .. note:: *pbkdf2_hmac* is only available with OpenSSL 1.0 and newer. + + .. seealso:: Module :mod:`hmac` @@ -189,3 +230,5 @@ A hash object has the following methods: Wikipedia article with information on which algorithms have known issues and what that means regarding their use. + http://www.ietf.org/rfc/rfc2898.txt + PKCS #5: Password-Based Cryptography Specification Version 2.0 |