lisp/net/hmac-def.el

   1 ;;; hmac-def.el --- A macro for defining HMAC functions.
   2
   3 ;; Copyright (C) 1999, 2001, 2007-2017 Free Software Foundation, Inc.
   4
   5 ;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
   6 ;; Keywords: HMAC, RFC2104
   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 of the License, or
  13 ;; (at your option) 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.  If not, see <https://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24
  25 ;; This program is implemented from RFC2104,
  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
  33 HMAC function is H(KEY XOR opad, H(KEY XOR ipad, TEXT)):
  34
  35 H is a cryptographic hash function, such as SHA1 and MD5, which takes
  36 a string and return a digest of it (in binary form).
  37 B is a byte-length of a block size of H. (B=64 for both SHA1 and MD5.)
  38 L is a byte-length of hash outputs. (L=16 for MD5, L=20 for SHA1.)
  39 If 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
  83 ;;; hmac-def.el ends here