lisp/net/hmac-def.el

   1 ;;; hmac-def.el --- A macro for defining HMAC functions.
   2
   3 ;; Copyright (C) 1999, 2001, 2007, 2008  Free Software Foundation, Inc.
   4
   5 ;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
   6 ;; Keywords: HMAC, RFC 2104
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software; you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation; either version 3, or (at your option)
  13 ;; any later version.
  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
  21 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  22 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  23 ;; Boston, MA 02110-1301, USA.
  24
  25 ;;; Commentary:
  26
  27 ;; This program is implemented from RFC 2104,
  28 ;; "HMAC: Keyed-Hashing for Message Authentication".
  29
  30 ;;; Code:
  31
  32 (defmacro define-hmac-function (name H B L &optional bit)
  33   "Define a function NAME(TEXT KEY) which computes HMAC with function H.
  34
  35 HMAC function is H(KEY XOR opad, H(KEY XOR ipad, TEXT)):
  36
  37 H is a cryptographic hash function, such as SHA1 and MD5, which takes
  38 a string and return a digest of it (in binary form).
  39 B is a byte-length of a block size of H. (B=64 for both SHA1 and MD5.)
  40 L is a byte-length of hash outputs. (L=16 for MD5, L=20 for SHA1.)
  41 If BIT is non-nil, truncate output to specified bits."
  42   `(defun ,name (text key)
  43      ,(concat "Compute "
  44               (upcase (symbol-name name))
  45               " over TEXT with KEY.")
  46      (let ((key-xor-ipad (make-string ,B ?\x36))
  47            (key-xor-opad (make-string ,B ?\x5C))
  48            (len (length key))
  49            (pos 0))
  50        (unwind-protect
  51            (progn
  52              ;; if `key' is longer than the block size, apply hash function
  53              ;; to `key' and use the result as a real `key'.
  54              (if (> len ,B)
  55                  (setq key (,H key)
  56                        len ,L))
  57              (while (< pos len)
  58                (aset key-xor-ipad pos (logxor (aref key pos) ?\x36))
  59                (aset key-xor-opad pos (logxor (aref key pos) ?\x5C))
  60                (setq pos (1+ pos)))
  61              (setq key-xor-ipad (unwind-protect
  62                                     (concat key-xor-ipad text)
  63                                   (fillarray key-xor-ipad 0))
  64                    key-xor-ipad (unwind-protect
  65                                     (,H key-xor-ipad)
  66                                   (fillarray key-xor-ipad 0))
  67                    key-xor-opad (unwind-protect
  68                                     (concat key-xor-opad key-xor-ipad)
  69                                   (fillarray key-xor-opad 0))
  70                    key-xor-opad (unwind-protect
  71                                     (,H key-xor-opad)
  72                                   (fillarray key-xor-opad 0)))
  73              ;; now `key-xor-opad' contains
  74              ;; H(KEY XOR opad, H(KEY XOR ipad, TEXT)).
  75              ,(if (and bit (< (/ bit 8) L))
  76                   `(substring key-xor-opad 0 ,(/ bit 8))
  77                 ;; return a copy of `key-xor-opad'.
  78                 `(concat key-xor-opad)))
  79          ;; cleanup.
  80          (fillarray key-xor-ipad 0)
  81          (fillarray key-xor-opad 0)))))
  82
  83 (provide 'hmac-def)
  84
  85 ;; arch-tag: 645adcef-b835-4900-a10a-11f636c982b9
  86 ;;; hmac-def.el ends here