Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 1 | """HMAC (Keyed-Hashing for Message Authentication) Python module. |
| 2 | |
| 3 | Implements the HMAC algorithm as described by RFC 2104. |
| 4 | """ |
| 5 | |
Guido van Rossum | 3f42908 | 2007-07-10 13:35:52 +0000 | [diff] [blame] | 6 | trans_5C = bytes((x ^ 0x5C) for x in range(256)) |
| 7 | trans_36 = bytes((x ^ 0x36) for x in range(256)) |
Tim Peters | b64bec3 | 2001-09-18 02:26:39 +0000 | [diff] [blame] | 8 | |
Andrew M. Kuchling | 1ccdff9 | 2001-11-02 21:49:20 +0000 | [diff] [blame] | 9 | # The size of the digests returned by HMAC depends on the underlying |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 10 | # hashing module used. Use digest_size from the instance of HMAC instead. |
Andrew M. Kuchling | 1ccdff9 | 2001-11-02 21:49:20 +0000 | [diff] [blame] | 11 | digest_size = None |
| 12 | |
Tim Peters | 934d31b | 2004-03-20 20:11:29 +0000 | [diff] [blame] | 13 | # A unique object passed by HMAC.copy() to the HMAC constructor, in order |
| 14 | # that the latter return very quickly. HMAC("") in contrast is quite |
| 15 | # expensive. |
| 16 | _secret_backdoor_key = [] |
| 17 | |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 18 | class HMAC: |
| 19 | """RFC2104 HMAC class. |
| 20 | |
Andrew M. Kuchling | 1ccdff9 | 2001-11-02 21:49:20 +0000 | [diff] [blame] | 21 | This supports the API for Cryptographic Hash Functions (PEP 247). |
Tim Peters | b64bec3 | 2001-09-18 02:26:39 +0000 | [diff] [blame] | 22 | """ |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 23 | blocksize = 64 # 512-bit HMAC; can be changed in subclasses. |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 24 | |
| 25 | def __init__(self, key, msg = None, digestmod = None): |
| 26 | """Create a new HMAC object. |
| 27 | |
| 28 | key: key for the keyed hash object. |
| 29 | msg: Initial input for the hash, if provided. |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 30 | digestmod: A module supporting PEP 247. *OR* |
| 31 | A hashlib constructor returning a new hash object. |
| 32 | Defaults to hashlib.md5. |
Guido van Rossum | 3f42908 | 2007-07-10 13:35:52 +0000 | [diff] [blame] | 33 | |
| 34 | Note: key and msg must be bytes objects. |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 35 | """ |
Tim Peters | 934d31b | 2004-03-20 20:11:29 +0000 | [diff] [blame] | 36 | |
| 37 | if key is _secret_backdoor_key: # cheap |
| 38 | return |
| 39 | |
Guido van Rossum | 39478e8 | 2007-08-27 17:23:59 +0000 | [diff] [blame] | 40 | assert isinstance(key, bytes), repr(key) |
Guido van Rossum | 3f42908 | 2007-07-10 13:35:52 +0000 | [diff] [blame] | 41 | |
Raymond Hettinger | 7fdfc2d | 2002-05-31 17:49:10 +0000 | [diff] [blame] | 42 | if digestmod is None: |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 43 | import hashlib |
| 44 | digestmod = hashlib.md5 |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 45 | |
Guido van Rossum | d59da4b | 2007-05-22 18:11:13 +0000 | [diff] [blame] | 46 | if hasattr(digestmod, '__call__'): |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 47 | self.digest_cons = digestmod |
| 48 | else: |
Guido van Rossum | 3f42908 | 2007-07-10 13:35:52 +0000 | [diff] [blame] | 49 | self.digest_cons = lambda d=b'': digestmod.new(d) |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 50 | |
| 51 | self.outer = self.digest_cons() |
| 52 | self.inner = self.digest_cons() |
| 53 | self.digest_size = self.inner.digest_size |
Tim Peters | 8876848 | 2001-11-13 21:51:26 +0000 | [diff] [blame] | 54 | |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 55 | blocksize = self.blocksize |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 56 | if len(key) > blocksize: |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 57 | key = self.digest_cons(key).digest() |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 58 | |
Guido van Rossum | 3f42908 | 2007-07-10 13:35:52 +0000 | [diff] [blame] | 59 | key = key + bytes(blocksize - len(key)) |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 60 | self.outer.update(key.translate(trans_5C)) |
| 61 | self.inner.update(key.translate(trans_36)) |
Raymond Hettinger | 094662a | 2002-06-01 01:29:16 +0000 | [diff] [blame] | 62 | if msg is not None: |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 63 | self.update(msg) |
| 64 | |
| 65 | ## def clear(self): |
| 66 | ## raise NotImplementedError, "clear() method not available in HMAC." |
| 67 | |
| 68 | def update(self, msg): |
| 69 | """Update this hashing object with the string msg. |
| 70 | """ |
Guido van Rossum | 39478e8 | 2007-08-27 17:23:59 +0000 | [diff] [blame] | 71 | assert isinstance(msg, bytes), repr(msg) |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 72 | self.inner.update(msg) |
| 73 | |
| 74 | def copy(self): |
| 75 | """Return a separate copy of this hashing object. |
| 76 | |
| 77 | An update to this copy won't affect the original object. |
| 78 | """ |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 79 | other = self.__class__(_secret_backdoor_key) |
Gregory P. Smith | f21a5f7 | 2005-08-21 18:45:59 +0000 | [diff] [blame] | 80 | other.digest_cons = self.digest_cons |
Tim Peters | 934d31b | 2004-03-20 20:11:29 +0000 | [diff] [blame] | 81 | other.digest_size = self.digest_size |
Andrew M. Kuchling | 1ccdff9 | 2001-11-02 21:49:20 +0000 | [diff] [blame] | 82 | other.inner = self.inner.copy() |
| 83 | other.outer = self.outer.copy() |
| 84 | return other |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 85 | |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 86 | def _current(self): |
| 87 | """Return a hash object for the current state. |
| 88 | |
| 89 | To be used only internally with digest() and hexdigest(). |
| 90 | """ |
| 91 | h = self.outer.copy() |
| 92 | h.update(self.inner.digest()) |
| 93 | return h |
| 94 | |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 95 | def digest(self): |
| 96 | """Return the hash value of this hashing object. |
| 97 | |
| 98 | This returns a string containing 8-bit data. The object is |
| 99 | not altered in any way by this function; you can continue |
| 100 | updating the object after calling this function. |
| 101 | """ |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 102 | h = self._current() |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 103 | return h.digest() |
| 104 | |
| 105 | def hexdigest(self): |
| 106 | """Like digest(), but returns a string of hexadecimal digits instead. |
| 107 | """ |
Thomas Wouters | 902d6eb | 2007-01-09 23:18:33 +0000 | [diff] [blame] | 108 | h = self._current() |
| 109 | return h.hexdigest() |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 110 | |
| 111 | def new(key, msg = None, digestmod = None): |
| 112 | """Create a new hashing object and return it. |
| 113 | |
| 114 | key: The starting key for the hash. |
| 115 | msg: if available, will immediately be hashed into the object's starting |
Tim Peters | b64bec3 | 2001-09-18 02:26:39 +0000 | [diff] [blame] | 116 | state. |
Guido van Rossum | 8ceef41 | 2001-09-11 15:54:00 +0000 | [diff] [blame] | 117 | |
| 118 | You can now feed arbitrary strings into the object using its update() |
| 119 | method, and can ask for the hash value at any time by calling its digest() |
| 120 | method. |
| 121 | """ |
| 122 | return HMAC(key, msg, digestmod) |