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[bpt/emacs.git] / lisp / net / hmac-def.el
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1;;; hmac-def.el --- A macro for defining HMAC functions.
2
ba318903 3;; Copyright (C) 1999, 2001, 2007-2014 Free Software Foundation, Inc.
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4
5;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
88f4758e 6;; Keywords: HMAC, RFC2104
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7
8;; This file is part of GNU Emacs.
9
874a927a 10;; GNU Emacs is free software: you can redistribute it and/or modify
0cd1fac2 11;; it under the terms of the GNU General Public License as published by
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12;; the Free Software Foundation, either version 3 of the License, or
13;; (at your option) any later version.
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14
15;; GNU Emacs is distributed in the hope that it will be useful,
16;; but WITHOUT ANY WARRANTY; without even the implied warranty of
17;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18;; GNU General Public License for more details.
19
20;; You should have received a copy of the GNU General Public License
874a927a 21;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
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22
23;;; Commentary:
24
88f4758e 25;; This program is implemented from RFC2104,
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26;; "HMAC: Keyed-Hashing for Message Authentication".
27
28;;; Code:
29
30(defmacro define-hmac-function (name H B L &optional bit)
31 "Define a function NAME(TEXT KEY) which computes HMAC with function H.
32
33HMAC function is H(KEY XOR opad, H(KEY XOR ipad, TEXT)):
34
35H is a cryptographic hash function, such as SHA1 and MD5, which takes
36a string and return a digest of it (in binary form).
37B is a byte-length of a block size of H. (B=64 for both SHA1 and MD5.)
38L is a byte-length of hash outputs. (L=16 for MD5, L=20 for SHA1.)
39If BIT is non-nil, truncate output to specified bits."
40 `(defun ,name (text key)
41 ,(concat "Compute "
42 (upcase (symbol-name name))
43 " over TEXT with KEY.")
44 (let ((key-xor-ipad (make-string ,B ?\x36))
45 (key-xor-opad (make-string ,B ?\x5C))
46 (len (length key))
47 (pos 0))
48 (unwind-protect
49 (progn
50 ;; if `key' is longer than the block size, apply hash function
51 ;; to `key' and use the result as a real `key'.
52 (if (> len ,B)
53 (setq key (,H key)
54 len ,L))
55 (while (< pos len)
56 (aset key-xor-ipad pos (logxor (aref key pos) ?\x36))
57 (aset key-xor-opad pos (logxor (aref key pos) ?\x5C))
58 (setq pos (1+ pos)))
59 (setq key-xor-ipad (unwind-protect
60 (concat key-xor-ipad text)
61 (fillarray key-xor-ipad 0))
62 key-xor-ipad (unwind-protect
63 (,H key-xor-ipad)
64 (fillarray key-xor-ipad 0))
65 key-xor-opad (unwind-protect
66 (concat key-xor-opad key-xor-ipad)
67 (fillarray key-xor-opad 0))
68 key-xor-opad (unwind-protect
69 (,H key-xor-opad)
70 (fillarray key-xor-opad 0)))
71 ;; now `key-xor-opad' contains
72 ;; H(KEY XOR opad, H(KEY XOR ipad, TEXT)).
73 ,(if (and bit (< (/ bit 8) L))
74 `(substring key-xor-opad 0 ,(/ bit 8))
75 ;; return a copy of `key-xor-opad'.
76 `(concat key-xor-opad)))
77 ;; cleanup.
78 (fillarray key-xor-ipad 0)
79 (fillarray key-xor-opad 0)))))
80
81(provide 'hmac-def)
82
0cd1fac2 83;;; hmac-def.el ends here