1 ;;; hmac-def.el --- Functions/macros for defining HMAC functions.
3 ;; Copyright (C) 1999 Shuhei KOBAYASHI
5 ;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
6 ;; Keywords: HMAC, RFC 2104
8 ;; This program is free software; you can redistribute it and/or
9 ;; modify it under the terms of the GNU General Public License as
10 ;; published by the Free Software Foundation; either version 2, or
11 ;; (at your option) any later version.
13 ;; This program is distributed in the hope that it will be useful,
14 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
15 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 ;; GNU General Public License for more details.
18 ;; You should have received a copy of the GNU General Public License
19 ;; along with this program; see the file COPYING. If not, write to
20 ;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
21 ;; Boston, MA 02111-1307, USA.
25 ;; See RFC 2104, "HMAC: Keyed-Hashing for Message Authentication"
26 ;; for definition of HMAC.
32 (defmacro hmac-unhex-string-macro (string length)
33 (let* ((len (eval length))
34 (dst (make-string (/ len 2) 0)))
39 (aset dst idx (+ (* (hmac-hex-to-int (aref str pos)) 16)
40 (hmac-hex-to-int (aref str (1+ pos)))))
45 ;; Note that H, B, and L will be evaluated multiple times. They are
46 ;; usually constants, so I don't want to bother to bind them locally.
47 (defmacro define-hmac-function (name H B L &optional bit)
48 "Define a function NAME which computes HMAC with hash function H.
50 HMAC function is H\(KEY XOR opad, H\(KEY XOR ipad, TEXT\)\):
52 H is a cryptographic hash function, such as SHA1 and MD5, which takes
53 a string and return a digest of it \(in hexadecimal form\).
54 B is a byte-length of a block size of H. \(B=64 for both SHA1 and MD5.\)
55 L is a byte-length of hash outputs. \(L=16 for MD5, L=20 for SHA1.\)
56 If BIT is non-nil, truncate output to specified bits."
57 `(defun ,name (text key)
58 ,(concat "Compute " (upcase (symbol-name name)) " over TEXT with KEY.")
59 (let ((key-xor-ipad (make-string ,B ?\x36))
60 (key-xor-opad (make-string ,B ?\x5C))
64 (setq key (hmac-unhex-string-macro (,H key) ,(* L 2)))
67 (aset key-xor-ipad pos (logxor (aref key pos) ?\x36))
68 (aset key-xor-opad pos (logxor (aref key pos) ?\x5C))
70 ;; If outer `hmac-unhex-string-macro' is removed, return value
71 ;; will be in hexadecimal form. It is useful for test.
72 ,(if (and bit (< (/ bit 8) L))
74 (hmac-unhex-string-macro
77 (hmac-unhex-string-macro
78 (,H (concat key-xor-ipad text))
82 `(hmac-unhex-string-macro
85 (hmac-unhex-string-macro
86 (,H (concat key-xor-ipad text))
92 ;;; hmac-def.el ends here.