Implement SCRAM-SHA-1 SASL mechanism

Fixes: debbugs:17636

* lisp/net/sasl-scram-rfc.el: New file.

* lisp/net/sasl.el (sasl-mechanisms): Remove SCRAM-MD5.  Add
SCRAM-SHA-1 first.
(sasl-mechanism-alist): Remove SCRAM-MD5 entry.  Add SCRAM-SHA-1
entry.

* test/automated/sasl-scram-rfc-tests.el: New file.

2 files changed, 163 insertions, 3 deletions

diff --git a/lisp/net/sasl-scram-rfc.el b/lisp/net/sasl-scram-rfc.el
new file mode 100644
index 00000000000..3d86da43f35
--- /dev/null
+++ b/lisp/net/sasl-scram-rfc.el
@@ -0,0 +1,160 @@
+;;; sasl-scram-rfc.el --- SCRAM-SHA-1 module for the SASL client framework  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2014  Free Software Foundation, Inc.
+
+;; Author: Magnus Henoch <magnus.henoch@gmail.com>
+
+;; 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 3 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This program is implemented from RFC 5802.  It implements the
+;; SCRAM-SHA-1 SASL mechanism.
+;;
+;; RFC 5802 foresees "hash agility", i.e. new mechanisms based on the
+;; same protocol but using a different hash function.  Likewise, this
+;; module attempts to separate generic and specific functions, which
+;; should make it easy to implement any future SCRAM-* SASL mechanism.
+;; It should be as simple as copying the SCRAM-SHA-1 section below and
+;; replacing all SHA-1 references.
+;;
+;; This module does not yet implement the variants with channel
+;; binding, i.e. SCRAM-*-PLUS.  That would require cooperation from
+;; the TLS library.
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'sasl)
+
+;;; SCRAM-SHA-1
+
+(require 'hex-util)
+(require 'rfc2104)
+
+(defconst sasl-scram-sha-1-steps
+  '(sasl-scram-client-first-message
+    sasl-scram-sha-1-client-final-message
+    sasl-scram-sha-1-authenticate-server))
+
+(defun sasl-scram-sha-1-client-final-message (client step)
+  (sasl-scram--client-final-message
+   ;; HMAC-SHA1 uses block length 64 and hash length 20; see RFC 2104.
+   'sha1 64 20 client step))
+
+(defun sasl-scram-sha-1-authenticate-server (client step)
+  (sasl-scram--authenticate-server
+   'sha1 64 20 client step))
+
+(put 'sasl-scram-sha-1 'sasl-mechanism
+     (sasl-make-mechanism "SCRAM-SHA-1" sasl-scram-sha-1-steps))
+
+(provide 'sasl-scram-sha-1)
+
+;;; Generic for SCRAM-*
+
+(defun sasl-scram-client-first-message (client _step)
+  (let ((c-nonce (sasl-unique-id)))
+    (sasl-client-set-property client 'c-nonce c-nonce))
+  (concat
+   ;; n = client doesn't support channel binding
+   "n,"
+   ;; TODO: where would we get authorization id from?
+   ","
+   (sasl-scram--client-first-message-bare client)))
+
+(defun sasl-scram--client-first-message-bare (client)
+  (let ((c-nonce (sasl-client-property client 'c-nonce)))
+    (concat
+     ;; TODO: saslprep username or disallow non-ASCII characters
+     "n=" (sasl-client-name client) ","
+     "r=" c-nonce)))
+
+(defun sasl-scram--client-final-message (hash-fun block-length hash-length client step)
+  (unless (string-match
+	   "^r=\\([^,]+\\),s=\\([^,]+\\),i=\\([0-9]+\\)\\(?:$\\|,\\)"
+	   (sasl-step-data step))
+    (sasl-error "Unexpected server response"))
+  (let* ((hmac-fun (lambda (text key)
+		     (decode-hex-string
+		      (rfc2104-hash hash-fun block-length hash-length key text))))
+	 (step-data (sasl-step-data step))
+	 (nonce (match-string 1 step-data))
+	 (salt-base64 (match-string 2 step-data))
+	 (iteration-count (string-to-number (match-string 3 step-data)))
+
+	 (c-nonce (sasl-client-property client 'c-nonce))
+	 ;; no channel binding, no authorization id
+	 (cbind-input "n,,"))
+    (unless (string-prefix-p c-nonce nonce)
+      (sasl-error "Invalid nonce from server"))
+    (let* ((client-final-message-without-proof
+	    (concat "c=" (base64-encode-string cbind-input) ","
+		    "r=" nonce))
+	   (password
+	    ;; TODO: either apply saslprep or disallow non-ASCII characters
+	    (sasl-read-passphrase
+	     (format "%s passphrase for %s: "
+		     (sasl-mechanism-name (sasl-client-mechanism client))
+		     (sasl-client-name client))))
+	   (salt (base64-decode-string salt-base64))
+	   (salted-password
+	    ;; Hi(str, salt, i):
+	    (let ((digest (concat salt (string 0 0 0 1)))
+		  (xored nil))
+	      (dotimes (_i iteration-count xored)
+		(setq digest (funcall hmac-fun digest password))
+		(setq xored (if (null xored)
+				digest
+			      (cl-map 'string 'logxor xored digest))))))
+	   (client-key
+	    (funcall hmac-fun "Client Key" salted-password))
+	   (stored-key (decode-hex-string (funcall hash-fun client-key)))
+	   (auth-message
+	    (concat
+	     (sasl-scram--client-first-message-bare client) ","
+	     step-data ","
+	     client-final-message-without-proof))
+	   (client-signature (funcall hmac-fun (encode-coding-string auth-message 'utf-8) stored-key))
+	   (client-proof (cl-map 'string 'logxor client-key client-signature))
+	   (client-final-message
+	    (concat client-final-message-without-proof ","
+		    "p=" (base64-encode-string client-proof))))
+      (sasl-client-set-property client 'auth-message auth-message)
+      (sasl-client-set-property client 'salted-password salted-password)
+      client-final-message)))
+
+(defun sasl-scram--authenticate-server (hash-fun block-length hash-length client step)
+  (cond
+   ((string-match "^e=\\([^,]+\\)" (sasl-step-data step))
+    (sasl-error (format "Server error: %s" (match-string 1 (sasl-step-data step)))))
+   ((string-match "^v=\\([^,]+\\)" (sasl-step-data step))
+    (let* ((hmac-fun (lambda (text key)
+		       (decode-hex-string
+			(rfc2104-hash hash-fun block-length hash-length key text))))
+	   (verifier (base64-decode-string (match-string 1 (sasl-step-data step))))
+	   (auth-message (sasl-client-property client 'auth-message))
+	   (salted-password (sasl-client-property client 'salted-password))
+	   (server-key (funcall hmac-fun "Server Key" salted-password))
+	   (expected-server-signature
+	    (funcall hmac-fun (encode-coding-string auth-message 'utf-8) server-key)))
+      (unless (string= expected-server-signature verifier)
+	(sasl-error "Server not authenticated"))))
+   (t
+    (sasl-error "Invalid response from server"))))
+
+(provide 'sasl-scram-rfc)
+;;; sasl-scram-rfc.el ends here
diff --git a/lisp/net/sasl.el b/lisp/net/sasl.el
index 648e6227497..e59ed5d43aa 100644
--- a/lisp/net/sasl.el
+++ b/lisp/net/sasl.el
@@ -35,8 +35,8 @@
 ;;; Code:
 
 (defvar sasl-mechanisms
-  '("CRAM-MD5" "DIGEST-MD5" "PLAIN" "LOGIN" "ANONYMOUS"
-    "NTLM" "SCRAM-MD5"))
+  '("SCRAM-SHA-1" "CRAM-MD5" "DIGEST-MD5" "PLAIN" "LOGIN" "ANONYMOUS"
+    "NTLM"))
 
 (defvar sasl-mechanism-alist
   '(("CRAM-MD5" sasl-cram)
@@ -45,7 +45,7 @@
     ("LOGIN" sasl-login)
     ("ANONYMOUS" sasl-anonymous)
     ("NTLM" sasl-ntlm)
-    ("SCRAM-MD5" sasl-scram)))
+    ("SCRAM-SHA-1" sasl-scram-sha-1)))
 
 (defvar sasl-unique-id-function #'sasl-unique-id-function)