1 ;;; sasl-scram-rfc.el --- SCRAM-SHA-1 module for the SASL client framework -*- lexical-binding: t; -*-
3 ;; Copyright (C) 2014-2016 Free Software Foundation, Inc.
5 ;; Author: Magnus Henoch <magnus.henoch@gmail.com>
8 ;; This file is part of GNU Emacs.
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.
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.
20 ;; You should have received a copy of the GNU General Public License
21 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
25 ;; This program is implemented from RFC 5802. It implements the
26 ;; SCRAM-SHA-1 SASL mechanism.
28 ;; RFC 5802 foresees "hash agility", i.e. new mechanisms based on the
29 ;; same protocol but using a different hash function. Likewise, this
30 ;; module attempts to separate generic and specific functions, which
31 ;; should make it easy to implement any future SCRAM-* SASL mechanism.
32 ;; It should be as simple as copying the SCRAM-SHA-1 section below and
33 ;; replacing all SHA-1 references.
35 ;; This module does not yet implement the variants with channel
36 ;; binding, i.e. SCRAM-*-PLUS. That would require cooperation from
41 (ignore-errors (require 'cl-lib))
47 ;;; Generic for SCRAM-*
49 (defun sasl-scram-client-first-message (client _step)
50 (let ((c-nonce (sasl-unique-id)))
51 (sasl-client-set-property client 'c-nonce c-nonce))
53 ;; n = client doesn't support channel binding
55 ;; TODO: where would we get authorization id from?
57 (sasl-scram--client-first-message-bare client)))
59 (defun sasl-scram--client-first-message-bare (client)
60 (let ((c-nonce (sasl-client-property client 'c-nonce)))
62 ;; TODO: saslprep username or disallow non-ASCII characters
63 "n=" (sasl-client-name client) ","
67 (declare-function sasl-cl-coerce "sasl-scram-rfc")
68 (declare-function sasl-cl-mapcar-many "sasl-scram-rfc")
70 (defalias 'sasl-cl-map 'cl-map)
71 (defun sasl-cl-mapcar-many (func seqs)
74 (n (apply 'min (mapcar 'length seqs)))
76 (args (copy-sequence seqs))
78 (setq seqs (copy-sequence seqs))
80 (setq p1 seqs p2 args)
85 (setcar p1 (cdr (car p1))))
87 (setq p1 (cdr p1) p2 (cdr p2)))
88 (push (apply func args) res)
94 (let ((n (min (length x) (length y)))
96 (while (< (setq i (1+ i)) n)
98 (if (consp x) (pop x) (aref x i))
99 (if (consp y) (pop y) (aref y i)))
103 (defun sasl-cl-coerce (x type)
104 "Coerce OBJECT to type TYPE.
105 TYPE is a Common Lisp type specifier.
107 (cond ((eq type 'list) (if (listp x) x (append x nil)))
108 ((eq type 'vector) (if (vectorp x) x (vconcat x)))
109 ((eq type 'string) (if (stringp x) x (concat x)))
110 ((eq type 'array) (if (arrayp x) x (vconcat x)))
111 ((and (eq type 'character) (stringp x) (= (length x) 1)) (aref x 0))
112 ((and (eq type 'character) (symbolp x))
113 (sasl-cl-coerce (symbol-name x) type))
114 ((eq type 'float) (float x))
115 ;;((cl-typep x type) x)
116 (t (error "Can't coerce %s to type %s" x type))))
118 (defun sasl-cl-map (type func seq &rest rest)
119 "Map a FUNCTION across one or more SEQUENCEs, returning a sequence.
120 TYPE is the sequence type to return.
121 \n(fn TYPE FUNCTION SEQUENCE...)"
124 (if (or (cdr rest) (nlistp seq) (nlistp (car rest)))
125 (setq res (sasl-cl-mapcar-many func (cons seq rest)))
128 (push (funcall func (pop seq) (pop y)) res))
129 (setq res (nreverse res)))
130 (setq res (mapcar func seq)))
131 (and type (sasl-cl-coerce res type)))))
133 (if (fboundp 'string-prefix-p)
134 (defalias 'sasl-string-prefix-p 'string-prefix-p)
135 (defun sasl-string-prefix-p (prefix string &optional ignore-case)
136 "Return non-nil if PREFIX is a prefix of STRING.
137 If IGNORE-CASE is non-nil, the comparison is done without paying attention
138 to case differences."
139 (let ((prefix-length (length prefix)))
140 (cond ((> prefix-length (length string)) nil)
142 (string-equal (downcase prefix)
143 (downcase (substring string 0 prefix-length))))
145 (string-equal prefix (substring string 0 prefix-length))))))))
147 (defun sasl-scram--client-final-message (hash-fun block-length hash-length client step)
148 (unless (string-match
149 "^r=\\([^,]+\\),s=\\([^,]+\\),i=\\([0-9]+\\)\\(?:$\\|,\\)"
150 (sasl-step-data step))
151 (sasl-error "Unexpected server response"))
152 (let* ((hmac-fun (lambda (text key)
154 (rfc2104-hash hash-fun block-length hash-length key text))))
155 (step-data (sasl-step-data step))
156 (nonce (match-string 1 step-data))
157 (salt-base64 (match-string 2 step-data))
158 (iteration-count (string-to-number (match-string 3 step-data)))
160 (c-nonce (sasl-client-property client 'c-nonce))
161 ;; no channel binding, no authorization id
163 (unless (sasl-string-prefix-p c-nonce nonce)
164 (sasl-error "Invalid nonce from server"))
165 (let* ((client-final-message-without-proof
166 (concat "c=" (base64-encode-string cbind-input) ","
169 ;; TODO: either apply saslprep or disallow non-ASCII characters
170 (sasl-read-passphrase
171 (format "%s passphrase for %s: "
172 (sasl-mechanism-name (sasl-client-mechanism client))
173 (sasl-client-name client))))
174 (salt (base64-decode-string salt-base64))
177 (let ((digest (concat salt (string 0 0 0 1)))
179 (dotimes (_i iteration-count xored)
180 (setq digest (funcall hmac-fun digest password))
181 (setq xored (if (null xored)
183 (sasl-cl-map 'string 'logxor xored digest))))))
185 (funcall hmac-fun "Client Key" salted-password))
186 (stored-key (decode-hex-string (funcall hash-fun client-key)))
189 (sasl-scram--client-first-message-bare client) ","
191 client-final-message-without-proof))
192 (client-signature (funcall hmac-fun (encode-coding-string auth-message 'utf-8) stored-key))
193 (client-proof (sasl-cl-map 'string 'logxor client-key client-signature))
194 (client-final-message
195 (concat client-final-message-without-proof ","
196 "p=" (base64-encode-string client-proof))))
197 (sasl-client-set-property client 'auth-message auth-message)
198 (sasl-client-set-property client 'salted-password salted-password)
199 client-final-message)))
201 (defun sasl-scram--authenticate-server (hash-fun block-length hash-length client step)
203 ((string-match "^e=\\([^,]+\\)" (sasl-step-data step))
204 (sasl-error (format "Server error: %s" (match-string 1 (sasl-step-data step)))))
205 ((string-match "^v=\\([^,]+\\)" (sasl-step-data step))
206 (let* ((hmac-fun (lambda (text key)
208 (rfc2104-hash hash-fun block-length hash-length key text))))
209 (verifier (base64-decode-string (match-string 1 (sasl-step-data step))))
210 (auth-message (sasl-client-property client 'auth-message))
211 (salted-password (sasl-client-property client 'salted-password))
212 (server-key (funcall hmac-fun "Server Key" salted-password))
213 (expected-server-signature
214 (funcall hmac-fun (encode-coding-string auth-message 'utf-8) server-key)))
215 (unless (string= expected-server-signature verifier)
216 (sasl-error "Server not authenticated"))))
218 (sasl-error "Invalid response from server"))))
222 (defconst sasl-scram-sha-1-steps
223 '(sasl-scram-client-first-message
224 sasl-scram-sha-1-client-final-message
225 sasl-scram-sha-1-authenticate-server))
227 (defun sasl-scram-sha-1-client-final-message (client step)
228 (sasl-scram--client-final-message
229 ;; HMAC-SHA1 uses block length 64 and hash length 20; see RFC 2104.
230 'sha1 64 20 client step))
232 (defun sasl-scram-sha-1-authenticate-server (client step)
233 (sasl-scram--authenticate-server
234 'sha1 64 20 client step))
236 ;; This needs to be at the end, because of how `sasl-make-mechanism'
237 ;; handles step function names.
238 (put 'sasl-scram-sha-1 'sasl-mechanism
239 (sasl-make-mechanism "SCRAM-SHA-1" sasl-scram-sha-1-steps))
241 (put 'sasl-scram-rfc 'sasl-mechanism (get 'sasl-scram-sha-1 'sasl-mechanism))
243 (provide 'sasl-scram-sha-1)
245 (provide 'sasl-scram-rfc)
246 ;;; sasl-scram-rfc.el ends here