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Diffstat (limited to 'lisp/net/sasl-scram-rfc.el')
| -rw-r--r-- | lisp/net/sasl-scram-rfc.el | 160 |
1 files changed, 160 insertions, 0 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 |