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+;;; rfc2104.el --- RFC2104 Hashed Message Authentication Codes
+;; Copyright (C) 1998,1999 Free Software Foundation, Inc.
+
+;; Author: Simon Josefsson <jas@pdc.kth.se>
+;; Keywords: mail
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;;; This is a quick'n'dirty, low performance, implementation of RFC2104.
+;;;
+;;; Example:
+;;;
+;;; (require 'md5)
+;;; (rfc2104-hash 'md5 64 16 "Jefe" "what do ya want for nothing?")
+;;; "750c783e6ab0b503eaa86e310a5db738"
+;;;
+;;; 64 is block length of hash function (64 for MD5 and SHA), 16 is
+;;; resulting hash length (16 for MD5, 20 for SHA).
+;;;
+;;; Tested with Emacs 20.2 and XEmacs 20.3.
+
+;;; Release history:
+;;;
+;;; 1998-08-16  initial release posted to gnu.emacs.sources
+;;; 1998-08-17  use append instead of char-list-to-string
+;;; 1998-08-26  don't require hexl
+;;; 1998-09-25  renamed from hmac.el to rfc2104.el, also renamed functions
+;;; 1999-10-23  included in pgnus
+ 
+(eval-when-compile (require 'cl))
+
+;; Magic character for inner HMAC round. 0x36 == 54 == '6'
+(defconst rfc2104-ipad ?\x36)
+
+;; Magic character for outer HMAC round. 0x5C == 92 == '\'
+(defconst rfc2104-opad ?\x5C)
+
+;; Not so magic character for padding the key. 0x00
+(defconst rfc2104-zero ?\x00)
+
+;; Alist for converting hex to decimal.
+(defconst rfc2104-hex-alist 
+  '((?0 . 0)	      (?a . 10)	      (?A . 10)
+    (?1 . 1)	      (?b . 11)	      (?B . 11)
+    (?2 . 2)	      (?c . 12)	      (?C . 12)
+    (?3 . 3)	      (?d . 13)	      (?D . 13)
+    (?4 . 4)	      (?e . 14)	      (?E . 14)
+    (?5 . 5)	      (?f . 15)	      (?F . 15)
+    (?6 . 6)
+    (?7 . 7)
+    (?8 . 8)
+    (?9 . 9)))
+
+(defun rfc2104-hex-to-int (str)
+  (if str
+      (if (listp str)
+	  (+ (* 16 (rfc2104-hex-to-int (cdr str)))
+	     (cdr (assoc (car str) rfc2104-hex-alist)))
+	(rfc2104-hex-to-int (reverse (append str nil))))
+    0))
+
+(defun rfc2104-hash (hash block-length hash-length key text)
+  (let* (;; if key is longer than B, reset it to HASH(key)
+	 (key (if (> (length key) block-length) 
+		  (funcall hash key) key))
+	 (k_ipad (append key nil))
+	 (k_opad (append key nil)))
+    ;; zero pad k_ipad/k_opad
+    (while (< (length k_ipad) block-length)
+      (setq k_ipad (append k_ipad (list rfc2104-zero))))
+    (while (< (length k_opad) block-length)
+      (setq k_opad (append k_opad (list rfc2104-zero))))
+    ;; XOR key with ipad/opad into k_ipad/k_opad
+    (setq k_ipad (mapcar (lambda (c) (logxor c rfc2104-ipad)) k_ipad))
+    (setq k_opad (mapcar (lambda (c) (logxor c rfc2104-opad)) k_opad))
+    ;; perform inner hash
+    (let ((first-round (funcall hash (concat k_ipad text)))
+	  de-hexed)
+      (while (< 0 (length first-round))
+	(push (rfc2104-hex-to-int (substring first-round -2)) de-hexed)
+	(setq first-round (substring first-round 0 -2)))
+      ;; perform outer hash
+      (funcall hash (concat k_opad de-hexed)))))
+
+(provide 'rfc2104)
+
+;;; rfc2104.el ends here