85 lines
2.9 KiB
EmacsLisp
85 lines
2.9 KiB
EmacsLisp
;;; hmac-def.el --- A macro for defining HMAC functions. -*- lexical-binding: t -*-
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;; Copyright (C) 1999, 2001, 2007-2024 Free Software Foundation, Inc.
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;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
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;; Keywords: HMAC, RFC2104
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; This program is implemented from RFC2104,
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;; "HMAC: Keyed-Hashing for Message Authentication".
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;;; Code:
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(defmacro define-hmac-function (name H B L &optional bit)
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"Define a function NAME(TEXT KEY) which computes HMAC with function H.
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HMAC function is H(KEY XOR opad, H(KEY XOR ipad, TEXT)):
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H is a cryptographic hash function, such as SHA1 and MD5, which takes
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a string and return a digest of it (in binary form).
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B is a byte length of a block size of H. (B=64 for both SHA1 and MD5.)
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L is a byte length of hash outputs. (L=16 for MD5, L=20 for SHA1.)
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If BIT is non-nil, truncate output to specified bits."
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(declare (indent defun))
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`(defun ,name (text key)
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,(concat "Compute "
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(upcase (symbol-name name))
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" over TEXT with KEY.")
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(let ((key-xor-ipad (make-string ,B ?\x36))
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(key-xor-opad (make-string ,B ?\x5C))
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(len (length key))
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(pos 0))
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(unwind-protect
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(progn
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;; if `key' is longer than the block size, apply hash function
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;; to `key' and use the result as a real `key'.
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(if (> len ,B)
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(setq key (,H key)
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len ,L))
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(while (< pos len)
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(aset key-xor-ipad pos (logxor (aref key pos) ?\x36))
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(aset key-xor-opad pos (logxor (aref key pos) ?\x5C))
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(setq pos (1+ pos)))
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(setq key-xor-ipad (unwind-protect
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(concat key-xor-ipad text)
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(fillarray key-xor-ipad 0))
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key-xor-ipad (unwind-protect
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(,H key-xor-ipad)
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(fillarray key-xor-ipad 0))
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key-xor-opad (unwind-protect
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(concat key-xor-opad key-xor-ipad)
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(fillarray key-xor-opad 0))
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key-xor-opad (unwind-protect
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(,H key-xor-opad)
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(fillarray key-xor-opad 0)))
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;; now `key-xor-opad' contains
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;; H(KEY XOR opad, H(KEY XOR ipad, TEXT)).
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,(if (and bit (< (/ bit 8) L))
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`(substring key-xor-opad 0 ,(/ bit 8))
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;; return a copy of `key-xor-opad'.
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'(concat key-xor-opad)))
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;; cleanup.
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(fillarray key-xor-ipad 0)
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(fillarray key-xor-opad 0)))))
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(provide 'hmac-def)
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;;; hmac-def.el ends here
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