;;; sasl-scram.el --- Compute SCRAM-MD5. -*- lexical-binding: t -*-
;; Copyright (C) 1999 Shuhei KOBAYASHI
;; Author: Shuhei KOBAYASHI <shuhei@aqua.ocn.ne.jp>
;; Kenichi OKADA <okada@opaopa.org>
;; Keywords: SCRAM-MD5, HMAC-MD5, SASL, IMAP, POP, ACAP
;; This file is part of FLIM (Faithful Library about Internet Message).
;; This program 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.
;; This program 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 this program; see the file COPYING. If not, write to
;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.
;;; Commentary:
;; This program is implemented from draft-newman-auth-scram-03.txt.
;;
;; It is caller's responsibility to base64-decode challenges and
;; base64-encode responses in IMAP4 AUTHENTICATE command.
;;
;; Passphrase should be longer than 16 bytes. (See RFC 2195)
;; Examples.
;;
;; (sasl-scram-md5-make-security-info nil t 0)
;; => "^A^@^@^@"
;;
;; (base64-encode-string
;; (sasl-scram-md5-make-client-msg-2
;; (base64-decode-string "dGVzdHNhbHQBAAAAaW1hcEBlbGVhbm9yLmlubm9zb2Z0LmNvbQBqaGNOWmxSdVBiemlGcCt2TFYrTkN3")
;; (base64-decode-string "AGNocmlzADx0NG40UGFiOUhCMEFtL1FMWEI3MmVnQGVsZWFub3IuaW5ub3NvZnQuY29tPg==")
;; (sasl-scram-md5-make-salted-pass
;; "secret stuff" "testsalt")
;; (sasl-scram-md5-make-security-info nil t 0)))
;; => "AQAAAMg9jU8CeB4KOfk7sUhSQPs="
;;
;; (base64-encode-string
;; (sasl-scram-md5-make-server-msg-2
;; (base64-decode-string "dGVzdHNhbHQBAAAAaW1hcEBlbGVhbm9yLmlubm9zb2Z0LmNvbQBqaGNOWmxSdVBiemlGcCt2TFYrTkN3")
;; (base64-decode-string "AGNocmlzADx0NG40UGFiOUhCMEFtL1FMWEI3MmVnQGVsZWFub3IuaW5ub3NvZnQuY29tPg==")
;; (sasl-scram-md5-make-security-info nil t 0)
;; "testsalt"
;; (sasl-scram-md5-make-salted-pass
;; "secret stuff" "testsalt")))
;; => "U0odqYw3B7XIIW0oSz65OQ=="
;;; Code:
(require 'sasl)
(require 'hmac-md5)
(defvar sasl-scram-md5-unique-id-function
sasl-unique-id-function)
(defconst sasl-scram-md5-steps
'(ignore ;no initial response
sasl-scram-md5-response-1
sasl-scram-md5-response-2
sasl-scram-md5-authenticate-server))
(defmacro sasl-scram-md5-security-info-no-security-layer (security-info)
`(eq (logand (aref ,security-info 0) 1) 1))
(defmacro sasl-scram-md5-security-info-integrity-protection-layer (security-info)
`(eq (logand (aref ,security-info 0) 2) 2))
(defmacro sasl-scram-md5-security-info-buffer-size (security-info)
`(let ((ssecinfo ,security-info))
(+ (lsh (aref ssecinfo 1) 16)
(lsh (aref ssecinfo 2) 8)
(aref ssecinfo 3))))
(defun sasl-scram-md5-make-security-info (integrity-protection-layer
no-security-layer buffer-size)
(let ((csecinfo (make-string 4 0)))
(when integrity-protection-layer
(aset csecinfo 0 2))
(if no-security-layer
(aset csecinfo 0 (logior (aref csecinfo 0) 1))
(aset csecinfo 1
(lsh (logand buffer-size (lsh 255 16)) -16))
(aset csecinfo 2
(lsh (logand buffer-size (lsh 255 8)) -8))
(aset csecinfo 3 (logand buffer-size 255)))
csecinfo))
(defun sasl-scram-md5-make-unique-nonce () ; 8*OCTET, globally unique.
;; For example, concatenated string of process-identifier, system-clock,
;; sequence-number, random-number, and domain-name.
(let* ((sasl-unique-id-function sasl-scram-md5-unique-id-function)
(id (sasl-unique-id)))
(unwind-protect
(concat "<" id "@" (system-name) ">")
(fillarray id 0))))
(defun sasl-scram-md5-xor-string (str1 str2)
;; (length str1) == (length str2) == (length dst) == 16 (in SCRAM-MD5)
(let* ((len (length str1))
(dst (make-string len 0))
(pos 0))
(while (< pos len)
(aset dst pos (logxor (aref str1 pos) (aref str2 pos)))
(setq pos (1+ pos)))
dst))
(defun sasl-scram-md5-make-client-msg-1 (authenticate-id &optional authorize-id nonce)
"Make an initial client message from AUTHENTICATE-ID and AUTHORIZE-ID.
If AUTHORIZE-ID is the same as AUTHENTICATE-ID, it may be omitted."
(concat authorize-id "\0" authenticate-id "\0"
(or nonce
(sasl-scram-md5-make-unique-nonce))))
(defun sasl-scram-md5-parse-server-msg-1 (server-msg-1)
"Parse SERVER-MSG-1 and return a list of (SALT SECURITY-INFO SERVICE-ID)."
(if (and (> (length server-msg-1) 16)
(eq (string-match "[^@]+@[^\0]+\0" server-msg-1 12) 12))
(list (substring server-msg-1 0 8) ; salt
(substring server-msg-1 8 12) ; server-security-info
(substring server-msg-1 ; service-id
12 (1- (match-end 0))))
(sasl-error (format "Unexpected response: %s" server-msg-1))))
(defun sasl-scram-md5-server-salt (server-msg-1)
(car (sasl-scram-md5-parse-server-msg-1 server-msg-1)))
(defun sasl-scram-md5-make-salted-pass (passphrase salt)
(hmac-md5 salt passphrase))
(defun sasl-scram-md5-make-client-key (salted-pass)
(md5-binary salted-pass))
(defun sasl-scram-md5-make-client-verifier (client-key)
(md5-binary client-key))
(defun sasl-scram-md5-make-shared-key (server-msg-1
client-msg-1
client-security-info
client-verifier)
(let (buff)
(unwind-protect
(hmac-md5
(setq buff
(concat server-msg-1 client-msg-1 client-security-info))
client-verifier)
(fillarray buff 0))))
(defun sasl-scram-md5-make-client-proof (client-key shared-key)
(sasl-scram-md5-xor-string client-key shared-key))
(defun sasl-scram-md5-make-client-msg-2 (server-msg-1
client-msg-1
salted-pass
client-security-info)
(let (client-proof client-key shared-key client-verifier)
(setq client-key
(sasl-scram-md5-make-client-key salted-pass))
(setq client-verifier
(sasl-scram-md5-make-client-verifier client-key))
(setq shared-key
(unwind-protect
(sasl-scram-md5-make-shared-key
server-msg-1
client-msg-1
client-security-info
client-verifier)
(fillarray client-verifier 0)))
(setq client-proof
(unwind-protect
(sasl-scram-md5-make-client-proof
client-key shared-key)
(fillarray client-key 0)
(fillarray shared-key 0)))
(unwind-protect
(concat
client-security-info
client-proof)
(fillarray client-proof 0))))
(defun sasl-scram-md5-make-server-msg-2 (server-msg-1
client-msg-1
client-security-info
salt salted-pass)
(let ((server-salt
(hmac-md5 salt salted-pass))
buff)
(unwind-protect
(hmac-md5
(setq buff
(concat
client-msg-1
server-msg-1
client-security-info))
server-salt)
(fillarray server-salt 0)
(fillarray buff 0))))
(defun sasl-scram-md5-response-1 (client _step)
(sasl-client-set-property
client 'client-msg-1
(sasl-scram-md5-make-client-msg-1
(sasl-client-name client)
(sasl-client-property client 'authorize-id)
(sasl-client-property client 'nonce))))
(defun sasl-scram-md5-response-2 (client step)
(let* ((server-msg-1
(sasl-client-set-property
client 'server-msg-1
(sasl-step-data step)))
(salted-pass
(sasl-client-set-property
client 'salted-pass
(sasl-scram-md5-make-salted-pass
(sasl-read-passphrase
(format "SCRAM-MD5 passphrase for %s: "
(sasl-client-name client)))
(sasl-scram-md5-server-salt server-msg-1)))))
(sasl-client-set-property
client 'client-msg-2
(sasl-scram-md5-make-client-msg-2
server-msg-1
(sasl-client-property client 'client-msg-1)
salted-pass
(or (sasl-client-property client 'client-security-info)
(sasl-scram-md5-make-security-info nil t 0))))))
(defun sasl-scram-md5-authenticate-server (client step)
(let ((server-msg-2
(sasl-client-set-property
client 'server-msg-2
(sasl-step-data step)))
(server-msg-1
(sasl-client-property client 'server-msg-1)))
(if (string= server-msg-2
(sasl-scram-md5-make-server-msg-2
server-msg-1
(sasl-client-property client 'client-msg-1)
(or (sasl-client-property client 'client-security-info)
(sasl-scram-md5-make-security-info nil t 0))
(sasl-scram-md5-server-salt server-msg-1)
(sasl-client-property client 'salted-pass)))
" "
(sasl-error "SCRAM-MD5: authenticate server failed."))))
(put 'sasl-scram 'sasl-mechanism
(sasl-make-mechanism "SCRAM-MD5" sasl-scram-md5-steps))
(provide 'sasl-scram)
;;; sasl-scram.el ends here