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Diffstat (limited to 'lisp/net/nsm.el')
| -rw-r--r-- | lisp/net/nsm.el | 502 |
1 files changed, 502 insertions, 0 deletions
diff --git a/lisp/net/nsm.el b/lisp/net/nsm.el new file mode 100644 index 00000000000..2312e22d96a --- /dev/null +++ b/lisp/net/nsm.el @@ -0,0 +1,502 @@ +;;; nsm.el --- Network Security Manager + +;; Copyright (C) 2014-2015 Free Software Foundation, Inc. + +;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org> +;; Keywords: encryption, security, network + +;; 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: + +;;; Code: + +(require 'cl-lib) + +(defvar nsm-permanent-host-settings nil) +(defvar nsm-temporary-host-settings nil) + +(defgroup nsm nil + "Network Security Manager" + :version "25.1" + :group 'comm) + +(defcustom network-security-level 'medium + "How secure the network should be. +If a potential problem with the security of the network +connection is found, the user is asked to give input into how the +connection should be handled. + +The following values are possible: + +`low': Absolutely no checks are performed. +`medium': This is the default level, should be reasonable for most usage. +`high': This warns about additional things that many people would +not find useful. +`paranoid': On this level, the user is queried for most new connections. + +See the Emacs manual for a description of all things that are +checked and warned against." + :version "25.1" + :group 'nsm + :type '(choice (const :tag "Low" low) + (const :tag "Medium" medium) + (const :tag "High" high) + (const :tag "Paranoid" paranoid))) + +(defcustom nsm-settings-file (expand-file-name "network-security.data" + user-emacs-directory) + "The file the security manager settings will be stored in." + :version "25.1" + :group 'nsm + :type 'file) + +(defcustom nsm-save-host-names nil + "If non-nil, always save host names in the structures in `nsm-settings-file'. +By default, only hosts that have exceptions have their names +stored in plain text." + :version "25.1" + :group 'nsm + :type 'boolean) + +(defvar nsm-noninteractive nil + "If non-nil, the connection is opened in a non-interactive context. +This means that no queries should be performed.") + +(defun nsm-verify-connection (process host port &optional + save-fingerprint warn-unencrypted) + "Verify the security status of PROCESS that's connected to HOST:PORT. +If PROCESS is a gnutls connection, the certificate validity will +be examined. If it's a non-TLS connection, it may be compared +against previous connections. If the function determines that +there is something odd about the connection, the user will be +queried about what to do about it. + +The process it returned if everything is OK, and otherwise, the +process will be deleted and nil is returned. + +If SAVE-FINGERPRINT, always save the fingerprint of the +server (if the connection is a TLS connection). This is useful +to keep track of the TLS status of STARTTLS servers. + +If WARN-UNENCRYPTED, query the user if the connection is +unencrypted." + (if (eq network-security-level 'low) + process + (let* ((status (gnutls-peer-status process)) + (id (nsm-id host port)) + (settings (nsm-host-settings id))) + (cond + ((not (process-live-p process)) + nil) + ((not status) + ;; This is a non-TLS connection. + (nsm-check-plain-connection process host port settings + warn-unencrypted)) + (t + (let ((process + (nsm-check-tls-connection process host port status settings))) + (when (and process save-fingerprint + (null (nsm-host-settings id))) + (nsm-save-host host port status 'fingerprint 'always)) + process)))))) + +(defun nsm-check-tls-connection (process host port status settings) + (let ((process (nsm-check-certificate process host port status settings))) + (if (and process + (>= (nsm-level network-security-level) (nsm-level 'high))) + ;; Do further protocol-level checks if the security is high. + (nsm-check-protocol process host port status settings) + process))) + +(defun nsm-check-certificate (process host port status settings) + (let ((warnings (plist-get status :warnings))) + (cond + + ;; The certificate validated, but perhaps we want to do + ;; certificate pinning. + ((null warnings) + (cond + ((< (nsm-level network-security-level) (nsm-level 'high)) + process) + ;; The certificate is fine, but if we're paranoid, we might + ;; want to check whether it's changed anyway. + ((and (>= (nsm-level network-security-level) (nsm-level 'high)) + (not (nsm-fingerprint-ok-p host port status settings))) + (delete-process process) + nil) + ;; We haven't seen this before, and we're paranoid. + ((and (eq network-security-level 'paranoid) + (null settings) + (not (nsm-new-fingerprint-ok-p host port status))) + (delete-process process) + nil) + ((>= (nsm-level network-security-level) (nsm-level 'high)) + ;; Save the host fingerprint so that we can check it the + ;; next time we connect. + (nsm-save-host host port status 'fingerprint 'always) + process) + (t + process))) + + ;; The certificate did not validate. + ((not (equal network-security-level 'low)) + ;; We always want to pin the certificate of invalid connections + ;; to track man-in-the-middle or the like. + (if (not (nsm-fingerprint-ok-p host port status settings)) + (progn + (delete-process process) + nil) + ;; We have a warning, so query the user. + (if (and (not (nsm-warnings-ok-p status settings)) + (not (nsm-query + host port status 'conditions + "The TLS connection to %s:%s is insecure for the following reason%s:\n\n%s" + host port + (if (> (length warnings) 1) + "s" "") + (mapconcat #'gnutls-peer-status-warning-describe + warnings + "\n")))) + (progn + (delete-process process) + nil) + process)))))) + +(defun nsm-check-protocol (process host port status settings) + (let ((prime-bits (plist-get status :diffie-hellman-prime-bits)) + (encryption (format "%s-%s-%s" + (plist-get status :key-exchange) + (plist-get status :cipher) + (plist-get status :mac))) + (protocol (plist-get status :protocol))) + (cond + ((and prime-bits + (< prime-bits 1024) + (not (memq :diffie-hellman-prime-bits + (plist-get settings :conditions))) + (not + (nsm-query + host port status :diffie-hellman-prime-bits + "The Diffie-Hellman prime bits (%s) used for this connection to %s:%s is less than what is considered safe (%s)." + prime-bits host port 1024))) + (delete-process process) + nil) + ((and (string-match "\\bRC4\\b" encryption) + (not (memq :rc4 (plist-get settings :conditions))) + (not + (nsm-query + host port status :rc4 + "The connection to %s:%s uses the RC4 algorithm (%s), which is believed to be unsafe." + host port encryption))) + (delete-process process) + nil) + ((and protocol + (string-match "SSL" protocol) + (not (memq :ssl (plist-get settings :conditions))) + (not + (nsm-query + host port status :ssl + "The connection to %s:%s uses the %s protocol, which is believed to be unsafe." + host port protocol))) + (delete-process process) + nil) + (t + process)))) + +(defun nsm-fingerprint (status) + (plist-get (plist-get status :certificate) :public-key-id)) + +(defun nsm-fingerprint-ok-p (host port status settings) + (let ((did-query nil)) + (if (and settings + (not (eq (plist-get settings :fingerprint) :none)) + (not (equal (nsm-fingerprint status) + (plist-get settings :fingerprint))) + (not + (setq did-query + (nsm-query + host port status 'fingerprint + "The fingerprint for the connection to %s:%s has changed from %s to %s" + host port + (plist-get settings :fingerprint) + (nsm-fingerprint status))))) + ;; Not OK. + nil + (when did-query + ;; Remove any exceptions that have been set on the previous + ;; certificate. + (plist-put settings :conditions nil)) + t))) + +(defun nsm-new-fingerprint-ok-p (host port status) + (nsm-query + host port status 'fingerprint + "The fingerprint for the connection to %s:%s is new: %s" + host port + (nsm-fingerprint status))) + +(defun nsm-check-plain-connection (process host port settings warn-unencrypted) + ;; If this connection used to be TLS, but is now plain, then it's + ;; possible that we're being Man-In-The-Middled by a proxy that's + ;; stripping out STARTTLS announcements. + (cond + ((and (plist-get settings :fingerprint) + (not (eq (plist-get settings :fingerprint) :none)) + (not + (nsm-query + host port nil 'conditions + "The connection to %s:%s used to be an encrypted connection, but is now unencrypted. This might mean that there's a man-in-the-middle tapping this connection." + host port))) + (delete-process process) + nil) + ((and warn-unencrypted + (not (memq :unencrypted (plist-get settings :conditions))) + (not (nsm-query + host port nil 'conditions + "The connection to %s:%s is unencrypted." + host port))) + (delete-process process) + nil) + (t + process))) + +(defun nsm-query (host port status what message &rest args) + ;; If there is no user to answer queries, then say `no' to everything. + (if (or noninteractive + nsm-noninteractive) + nil + (let ((response + (condition-case nil + (nsm-query-user message args (nsm-format-certificate status)) + ;; Make sure we manage to close the process if the user hits + ;; `C-g'. + (quit 'no) + (error 'no)))) + (if (eq response 'no) + nil + (nsm-save-host host port status what response) + t)))) + +(defun nsm-query-user (message args cert) + (let ((buffer (get-buffer-create "*Network Security Manager*"))) + (with-help-window buffer + (with-current-buffer buffer + (erase-buffer) + (when (> (length cert) 0) + (insert cert "\n")) + (let ((start (point))) + (insert (apply 'format message args)) + (goto-char start) + ;; Fill the first line of the message, which usually + ;; contains lots of explanatory text. + (fill-region (point) (line-end-position))))) + (let ((responses '((?n . no) + (?s . session) + (?a . always))) + (prefix "") + response) + (while (not response) + (setq response + (cdr + (assq (downcase + (read-char + (concat prefix + "Continue connecting? (No, Session only, Always)"))) + responses))) + (unless response + (ding) + (setq prefix "Invalid choice. "))) + (kill-buffer buffer) + ;; If called from a callback, `read-char' will insert things + ;; into the pending input. Clear that. + (clear-this-command-keys) + response))) + +(defun nsm-save-host (host port status what permanency) + (let* ((id (nsm-id host port)) + (saved + (list :id id + :fingerprint (or (nsm-fingerprint status) + ;; Plain connection. + :none)))) + (when (or (eq what 'conditions) + nsm-save-host-names) + (nconc saved (list :host (format "%s:%s" host port)))) + ;; We either want to save/update the fingerprint or the conditions + ;; of the certificate/unencrypted connection. + (cond + ((eq what 'conditions) + (cond + ((not status) + (nconc saved '(:conditions (:unencrypted)))) + ((plist-get status :warnings) + (nconc saved + (list :conditions (plist-get status :warnings)))))) + ((not (eq what 'fingerprint)) + ;; Store additional protocol settings. + (let ((settings (nsm-host-settings id))) + (when settings + (setq saved settings)) + (if (plist-get saved :conditions) + (nconc (plist-get saved :conditions) (list what)) + (nconc saved (list :conditions (list what))))))) + (if (eq permanency 'always) + (progn + (nsm-remove-temporary-setting id) + (nsm-remove-permanent-setting id) + (push saved nsm-permanent-host-settings) + (nsm-write-settings)) + (nsm-remove-temporary-setting id) + (push saved nsm-temporary-host-settings)))) + +(defun nsm-write-settings () + (with-temp-file nsm-settings-file + (insert "(\n") + (dolist (setting nsm-permanent-host-settings) + (insert " ") + (prin1 setting (current-buffer)) + (insert "\n")) + (insert ")\n"))) + +(defun nsm-read-settings () + (setq nsm-permanent-host-settings + (with-temp-buffer + (insert-file-contents nsm-settings-file) + (goto-char (point-min)) + (ignore-errors (read (current-buffer)))))) + +(defun nsm-id (host port) + (concat "sha1:" (sha1 (format "%s:%s" host port)))) + +(defun nsm-host-settings (id) + (when (and (not nsm-permanent-host-settings) + (file-exists-p nsm-settings-file)) + (nsm-read-settings)) + (let ((result nil)) + (dolist (elem (append nsm-temporary-host-settings + nsm-permanent-host-settings)) + (when (and (not result) + (equal (plist-get elem :id) id)) + (setq result elem))) + result)) + +(defun nsm-warnings-ok-p (status settings) + (let ((ok t) + (conditions (plist-get settings :conditions))) + (dolist (warning (plist-get status :warnings)) + (unless (memq warning conditions) + (setq ok nil))) + ok)) + +(defun nsm-remove-permanent-setting (id) + (setq nsm-permanent-host-settings + (cl-delete-if + (lambda (elem) + (equal (plist-get elem :id) id)) + nsm-permanent-host-settings))) + +(defun nsm-remove-temporary-setting (id) + (setq nsm-temporary-host-settings + (cl-delete-if + (lambda (elem) + (equal (plist-get elem :id) id)) + nsm-temporary-host-settings))) + +(defun nsm-format-certificate (status) + (let ((cert (plist-get status :certificate))) + (when cert + (with-temp-buffer + (insert + "Certificate information\n" + "Issued by:" + (nsm-certificate-part (plist-get cert :issuer) "CN" t) "\n" + "Issued to:" + (or (nsm-certificate-part (plist-get cert :subject) "O") + (nsm-certificate-part (plist-get cert :subject) "OU" t)) + "\n" + "Hostname:" + (nsm-certificate-part (plist-get cert :subject) "CN" t) "\n") + (when (and (plist-get cert :public-key-algorithm) + (plist-get cert :signature-algorithm)) + (insert + "Public key:" (plist-get cert :public-key-algorithm) + ", signature: " (plist-get cert :signature-algorithm) "\n")) + (when (and (plist-get status :key-exchange) + (plist-get status :cipher) + (plist-get status :mac) + (plist-get status :protocol)) + (insert + "Protocol:" (plist-get status :protocol) + ", key: " (plist-get status :key-exchange) + ", cipher: " (plist-get status :cipher) + ", mac: " (plist-get status :mac) "\n")) + (when (plist-get cert :certificate-security-level) + (insert + "Security level:" + (propertize (plist-get cert :certificate-security-level) + 'face 'bold) + "\n")) + (insert + "Valid:From " (plist-get cert :valid-from) + " to " (plist-get cert :valid-to) "\n\n") + (goto-char (point-min)) + (while (re-search-forward "^[^:]+:" nil t) + (insert (make-string (- 20 (current-column)) ? ))) + (buffer-string))))) + +(defun nsm-certificate-part (string part &optional full) + (let ((part (cadr (assoc part (nsm-parse-subject string))))) + (cond + (part part) + (full string) + (t nil)))) + +(defun nsm-parse-subject (string) + (with-temp-buffer + (insert string) + (goto-char (point-min)) + (let ((start (point)) + (result nil)) + (while (not (eobp)) + (push (replace-regexp-in-string + "[\\]\\(.\\)" "\\1" + (buffer-substring start + (if (re-search-forward "[^\\]," nil 'move) + (1- (point)) + (point)))) + result) + (setq start (point))) + (mapcar + (lambda (elem) + (let ((pos (cl-position ?= elem))) + (if pos + (list (substring elem 0 pos) + (substring elem (1+ pos))) + elem))) + (nreverse result))))) + +(defun nsm-level (symbol) + "Return a numerical level for SYMBOL for easier comparison." + (cond + ((eq symbol 'low) 0) + ((eq symbol 'medium) 1) + ((eq symbol 'high) 2) + (t 3))) + +(provide 'nsm) + +;;; nsm.el ends here |