bug#17636: Implement SCRAM-SHA-1 SASL mechanism

[Magnus Henoch <magnus.henoch@gmail.com>]

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rfc2104.el was rewritten for speed in 2008, and seems to be about
twice as fast as hmac-*.el.  I think hmac-*.el could be deprecated and
eventually removed; the only use in the Emacs tree is in sasl-cram.el.

So here is a new and improved patch for implementing SCRAM-SHA-1, that
uses the existing rfc2104.el instead of adding hmac-sha1.el.

Would it be okay for a module in lisp/net to depend on a module in
lisp/gnus?

Regards,
Magnus


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From 9e40ec05bd7e628432abc8570a8c62718a9e5a56 Mon Sep 17 00:00:00 2001
From: Magnus Henoch <magnus.henoch@gmail.com>
Date: Thu, 29 May 2014 20:46:30 +0100
Subject: [PATCH] Implement SCRAM-SHA-1 SASL mechanism

Remove all references to SCRAM-MD5, which never made it into an RFC,
and whose implementation wasn't merged from FLIM to Emacs.  Use HMAC /
RFC 2104 implementation from rfc2104.el in Gnus.

* 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.
---
 lisp/ChangeLog                         |   9 ++
 lisp/net/sasl-scram-rfc.el             | 160 +++++++++++++++++++++++++++++++++
 lisp/net/sasl.el                       |   6 +-
 test/ChangeLog                         |   4 +
 test/automated/sasl-scram-rfc-tests.el |  50 +++++++++++
 5 files changed, 226 insertions(+), 3 deletions(-)
 create mode 100644 lisp/net/sasl-scram-rfc.el
 create mode 100644 test/automated/sasl-scram-rfc-tests.el

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 552b43a..17cdbef 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,12 @@
+2014-10-09  Magnus Henoch  <magnus.henoch@gmail.com>
+
+	* 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.
+
+	* net/sasl-scram-rfc.el: New file.
+
 2014-07-14  Daniel Colascione  <dancol@dancol.org>
 
 	* progmodes/cc-langs.el: Change comments from `cl-macroexpand-all'
diff --git a/lisp/net/sasl-scram-rfc.el b/lisp/net/sasl-scram-rfc.el
new file mode 100644
index 0000000..3d86da4
--- /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 03a8f72..adb13b9 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)
 
diff --git a/test/ChangeLog b/test/ChangeLog
index 6e2f891..cc57b47 100644
--- a/test/ChangeLog
+++ b/test/ChangeLog
@@ -1,3 +1,7 @@
+2014-10-09  Magnus Henoch  <magnus.henoch@gmail.com>
+
+	* automated/sasl-scram-rfc-tests.el: New file.
+
 2014-07-12  Fabián Ezequiel Gallina  <fgallina@gnu.org>
 
 	* automated/python-tests.el (python-indent-block-enders-1)
diff --git a/test/automated/sasl-scram-rfc-tests.el b/test/automated/sasl-scram-rfc-tests.el
new file mode 100644
index 0000000..c747e5f
--- /dev/null
+++ b/test/automated/sasl-scram-rfc-tests.el
@@ -0,0 +1,50 @@
+;;; sasl-scram-rfc-tests.el --- tests for SCRAM-SHA-1       -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2014  Free Software Foundation, Inc.
+
+;; Author: Magnus Henoch <magnus.henoch@gmail.com>
+
+;; 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:
+
+;; Test cases from RFC 5802.
+
+;;; Code:
+
+(require 'sasl)
+(require 'sasl-scram-rfc)
+
+(ert-deftest sasl-scram-sha-1-test ()
+  ;; The following strings are taken from section 5 of RFC 5802.
+  (let ((client
+	 (sasl-make-client (sasl-find-mechanism '("SCRAM-SHA-1"))
+			   "user"
+			   "imap"
+			   "localhost"))
+	(data "r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,s=QSXCR+Q6sek8bf92,i=4096")
+	(c-nonce "fyko+d2lbbFgONRv9qkxdawL")
+	(sasl-read-passphrase
+	 (lambda (_prompt) (copy-sequence "pencil"))))
+    (sasl-client-set-property client 'c-nonce c-nonce)
+    (should
+     (equal
+      (sasl-scram-sha-1-client-final-message client (vector nil data))
+      "c=biws,r=fyko+d2lbbFgONRv9qkxdawL3rfcNHYJY1ZVvWVs7j,p=v0X8v3Bz2T0CJGbJQyF0X+HI4Ts="))
+
+    ;; This should not throw an error:
+    (sasl-scram-sha-1-authenticate-server client (vector nil "v=rmF9pqV8S7suAoZWja4dJRkFsKQ=
+"))))
+
+;;; sasl-scram-rfc-tests.el ends here
-- 
2.0.1