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   1 ;;; nsm.el --- Network Security Manager
   2
   3 ;; Copyright (C) 2014-2015 Free Software Foundation, Inc.
   4
   5 ;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
   6 ;; Keywords: encryption, security, network
   7
   8 ;; This file is part of GNU Emacs.
   9
  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.
  14
  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.
  19
  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/>.
  22
  23 ;;; Commentary:
  24
  25 ;;; Code:
  26
  27 (require 'cl-lib)
  28
  29 (defvar nsm-permanent-host-settings nil)
  30 (defvar nsm-temporary-host-settings nil)
  31
  32 (defgroup nsm nil
  33   "Network Security Manager"
  34   :version "25.1"
  35   :group 'comm)
  36
  37 (defcustom network-security-level 'medium
  38   "How secure the network should be.
  39 If a potential problem with the security of the network
  40 connection is found, the user is asked to give input into how the
  41 connection should be handled.
  42
  43 The following values are possible:
  44
  45 `low': Absolutely no checks are performed.
  46 `medium': This is the default level, should be reasonable for most usage.
  47 `high': This warns about additional things that many people would
  48 not find useful.
  49 `paranoid': On this level, the user is queried for most new connections.
  50
  51 See the Emacs manual for a description of all things that are
  52 checked and warned against."
  53   :version "25.1"
  54   :group 'nsm
  55   :type '(choice (const :tag "Low" low)
  56                  (const :tag "Medium" medium)
  57                  (const :tag "High" high)
  58                  (const :tag "Paranoid" paranoid)))
  59
  60 (defcustom nsm-settings-file (expand-file-name "network-security.data"
  61                                                  user-emacs-directory)
  62   "The file the security manager settings will be stored in."
  63   :version "25.1"
  64   :group 'nsm
  65   :type 'file)
  66
  67 (defcustom nsm-save-host-names nil
  68   "If non-nil, always save host names in the structures in `nsm-settings-file'.
  69 By default, only hosts that have exceptions have their names
  70 stored in plain text."
  71   :version "25.1"
  72   :group 'nsm
  73   :type 'boolean)
  74
  75 (defvar nsm-noninteractive nil
  76   "If non-nil, the connection is opened in a non-interactive context.
  77 This means that no queries should be performed.")
  78
  79 (declare-function gnutls-peer-status "gnutls.c" (proc))
  80
  81 (defun nsm-verify-connection (process host port &optional
  82                                       save-fingerprint warn-unencrypted)
  83   "Verify the security status of PROCESS that's connected to HOST:PORT.
  84 If PROCESS is a gnutls connection, the certificate validity will
  85 be examined.  If it's a non-TLS connection, it may be compared
  86 against previous connections.  If the function determines that
  87 there is something odd about the connection, the user will be
  88 queried about what to do about it.
  89
  90 The process it returned if everything is OK, and otherwise, the
  91 process will be deleted and nil is returned.
  92
  93 If SAVE-FINGERPRINT, always save the fingerprint of the
  94 server (if the connection is a TLS connection).  This is useful
  95 to keep track of the TLS status of STARTTLS servers.
  96
  97 If WARN-UNENCRYPTED, query the user if the connection is
  98 unencrypted."
  99   (if (eq network-security-level 'low)
 100       process
 101     (let* ((status (gnutls-peer-status process))
 102            (id (nsm-id host port))
 103            (settings (nsm-host-settings id)))
 104       (cond
 105        ((not (process-live-p process))
 106         nil)
 107        ((not status)
 108         ;; This is a non-TLS connection.
 109         (nsm-check-plain-connection process host port settings
 110                                     warn-unencrypted))
 111        (t
 112         (let ((process
 113                (nsm-check-tls-connection process host port status settings)))
 114           (when (and process save-fingerprint
 115                      (null (nsm-host-settings id)))
 116             (nsm-save-host host port status 'fingerprint 'always))
 117           process))))))
 118
 119 (defun nsm-check-tls-connection (process host port status settings)
 120   (let ((process (nsm-check-certificate process host port status settings)))
 121     (if (and process
 122              (>= (nsm-level network-security-level) (nsm-level 'high)))
 123         ;; Do further protocol-level checks if the security is high.
 124         (nsm-check-protocol process host port status settings)
 125       process)))
 126
 127 (declare-function gnutls-peer-status-warning-describe "gnutls.c"
 128                   (status-symbol))
 129
 130 (defun nsm-check-certificate (process host port status settings)
 131   (let ((warnings (plist-get status :warnings)))
 132     (cond
 133
 134      ;; The certificate validated, but perhaps we want to do
 135      ;; certificate pinning.
 136      ((null warnings)
 137       (cond
 138        ((< (nsm-level network-security-level) (nsm-level 'high))
 139         process)
 140        ;; The certificate is fine, but if we're paranoid, we might
 141        ;; want to check whether it's changed anyway.
 142        ((and (>= (nsm-level network-security-level) (nsm-level 'high))
 143              (not (nsm-fingerprint-ok-p host port status settings)))
 144         (delete-process process)
 145         nil)
 146        ;; We haven't seen this before, and we're paranoid.
 147        ((and (eq network-security-level 'paranoid)
 148              (null settings)
 149              (not (nsm-new-fingerprint-ok-p host port status)))
 150         (delete-process process)
 151         nil)
 152        ((>= (nsm-level network-security-level) (nsm-level 'high))
 153         ;; Save the host fingerprint so that we can check it the
 154         ;; next time we connect.
 155         (nsm-save-host host port status 'fingerprint 'always)
 156         process)
 157        (t
 158         process)))
 159
 160      ;; The certificate did not validate.
 161      ((not (equal network-security-level 'low))
 162       ;; We always want to pin the certificate of invalid connections
 163       ;; to track man-in-the-middle or the like.
 164       (if (not (nsm-fingerprint-ok-p host port status settings))
 165           (progn
 166             (delete-process process)
 167             nil)
 168         ;; We have a warning, so query the user.
 169         (if (and (not (nsm-warnings-ok-p status settings))
 170                  (not (nsm-query
 171                        host port status 'conditions
 172                        "The TLS connection to %s:%s is insecure for the following reason%s:\n\n%s"
 173                        host port
 174                        (if (> (length warnings) 1)
 175                            "s" "")
 176                        (mapconcat #'gnutls-peer-status-warning-describe
 177                                   warnings
 178                                   "\n"))))
 179             (progn
 180               (delete-process process)
 181               nil)
 182           process))))))
 183
 184 (defun nsm-check-protocol (process host port status settings)
 185   (let ((prime-bits (plist-get status :diffie-hellman-prime-bits))
 186         (encryption (format "%s-%s-%s"
 187                             (plist-get status :key-exchange)
 188                             (plist-get status :cipher)
 189                             (plist-get status :mac)))
 190         (protocol (plist-get status :protocol)))
 191     (cond
 192      ((and prime-bits
 193            (< prime-bits 1024)
 194            (not (memq :diffie-hellman-prime-bits
 195                       (plist-get settings :conditions)))
 196            (not
 197             (nsm-query
 198              host port status :diffie-hellman-prime-bits
 199              "The Diffie-Hellman prime bits (%s) used for this connection to %s:%s is less than what is considered safe (%s)."
 200              prime-bits host port 1024)))
 201       (delete-process process)
 202       nil)
 203      ((and (string-match "\\bRC4\\b" encryption)
 204            (not (memq :rc4 (plist-get settings :conditions)))
 205            (not
 206             (nsm-query
 207              host port status :rc4
 208              "The connection to %s:%s uses the RC4 algorithm (%s), which is believed to be unsafe."
 209              host port encryption)))
 210       (delete-process process)
 211       nil)
 212      ((and protocol
 213            (string-match "SSL" protocol)
 214            (not (memq :ssl (plist-get settings :conditions)))
 215            (not
 216             (nsm-query
 217              host port status :ssl
 218              "The connection to %s:%s uses the %s protocol, which is believed to be unsafe."
 219              host port protocol)))
 220       (delete-process process)
 221       nil)
 222      (t
 223       process))))
 224
 225 (defun nsm-fingerprint (status)
 226   (plist-get (plist-get status :certificate) :public-key-id))
 227
 228 (defun nsm-fingerprint-ok-p (host port status settings)
 229   (let ((did-query nil))
 230     (if (and settings
 231              (not (eq (plist-get settings :fingerprint) :none))
 232              (not (equal (nsm-fingerprint status)
 233                          (plist-get settings :fingerprint)))
 234              (not
 235               (setq did-query
 236                     (nsm-query
 237                      host port status 'fingerprint
 238                      "The fingerprint for the connection to %s:%s has changed from %s to %s"
 239                      host port
 240                      (plist-get settings :fingerprint)
 241                      (nsm-fingerprint status)))))
 242         ;; Not OK.
 243         nil
 244       (when did-query
 245         ;; Remove any exceptions that have been set on the previous
 246         ;; certificate.
 247         (plist-put settings :conditions nil))
 248       t)))
 249
 250 (defun nsm-new-fingerprint-ok-p (host port status)
 251   (nsm-query
 252    host port status 'fingerprint
 253    "The fingerprint for the connection to %s:%s is new: %s"
 254    host port
 255    (nsm-fingerprint status)))
 256
 257 (defun nsm-check-plain-connection (process host port settings warn-unencrypted)
 258   ;; If this connection used to be TLS, but is now plain, then it's
 259   ;; possible that we're being Man-In-The-Middled by a proxy that's
 260   ;; stripping out STARTTLS announcements.
 261   (cond
 262    ((and (plist-get settings :fingerprint)
 263          (not (eq (plist-get settings :fingerprint) :none))
 264          (not
 265           (nsm-query
 266            host port nil 'conditions
 267            "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."
 268            host port)))
 269     (delete-process process)
 270     nil)
 271    ((and warn-unencrypted
 272          (not (memq :unencrypted (plist-get settings :conditions)))
 273          (not (nsm-query
 274                host port nil 'conditions
 275                "The connection to %s:%s is unencrypted."
 276                host port)))
 277     (delete-process process)
 278     nil)
 279    (t
 280     process)))
 281
 282 (defun nsm-query (host port status what message &rest args)
 283   ;; If there is no user to answer queries, then say `no' to everything.
 284   (if (or noninteractive
 285           nsm-noninteractive)
 286       nil
 287     (let ((response
 288            (condition-case nil
 289                (nsm-query-user message args (nsm-format-certificate status))
 290              ;; Make sure we manage to close the process if the user hits
 291              ;; `C-g'.
 292              (quit 'no)
 293              (error 'no))))
 294       (if (eq response 'no)
 295           nil
 296         (nsm-save-host host port status what response)
 297         t))))
 298
 299 (defun nsm-query-user (message args cert)
 300   (let ((buffer (get-buffer-create "*Network Security Manager*")))
 301     (with-help-window buffer
 302       (with-current-buffer buffer
 303         (erase-buffer)
 304         (when (> (length cert) 0)
 305           (insert cert "\n"))
 306         (let ((start (point)))
 307           (insert (apply 'format message args))
 308           (goto-char start)
 309           ;; Fill the first line of the message, which usually
 310           ;; contains lots of explanatory text.
 311           (fill-region (point) (line-end-position)))))
 312     (let ((responses '((?n . no)
 313                        (?s . session)
 314                        (?a . always)))
 315           (prefix "")
 316           (cursor-in-echo-area t)
 317           response)
 318       (while (not response)
 319         (setq response
 320               (cdr
 321                (assq (downcase
 322                       (read-char
 323                        (concat prefix
 324                                "Continue connecting? (No, Session only, Always) ")))
 325                      responses)))
 326         (unless response
 327           (ding)
 328           (setq prefix "Invalid choice.  ")))
 329       (kill-buffer buffer)
 330       ;; If called from a callback, `read-char' will insert things
 331       ;; into the pending input.  Clear that.
 332       (clear-this-command-keys)
 333       response)))
 334
 335 (defun nsm-save-host (host port status what permanency)
 336   (let* ((id (nsm-id host port))
 337          (saved
 338           (list :id id
 339                 :fingerprint (or (nsm-fingerprint status)
 340                                  ;; Plain connection.
 341                                  :none))))
 342     (when (or (eq what 'conditions)
 343               nsm-save-host-names)
 344       (nconc saved (list :host (format "%s:%s" host port))))
 345     ;; We either want to save/update the fingerprint or the conditions
 346     ;; of the certificate/unencrypted connection.
 347     (cond
 348      ((eq what 'conditions)
 349       (cond
 350        ((not status)
 351         (nconc saved '(:conditions (:unencrypted))))
 352        ((plist-get status :warnings)
 353         (nconc saved
 354                (list :conditions (plist-get status :warnings))))))
 355      ((not (eq what 'fingerprint))
 356       ;; Store additional protocol settings.
 357       (let ((settings (nsm-host-settings id)))
 358         (when settings
 359           (setq saved settings))
 360         (if (plist-get saved :conditions)
 361             (nconc (plist-get saved :conditions) (list what))
 362           (nconc saved (list :conditions (list what)))))))
 363     (if (eq permanency 'always)
 364         (progn
 365           (nsm-remove-temporary-setting id)
 366           (nsm-remove-permanent-setting id)
 367           (push saved nsm-permanent-host-settings)
 368           (nsm-write-settings))
 369       (nsm-remove-temporary-setting id)
 370       (push saved nsm-temporary-host-settings))))
 371
 372 (defun nsm-write-settings ()
 373   (with-temp-file nsm-settings-file
 374     (insert "(\n")
 375     (dolist (setting nsm-permanent-host-settings)
 376       (insert " ")
 377       (prin1 setting (current-buffer))
 378       (insert "\n"))
 379     (insert ")\n")))
 380
 381 (defun nsm-read-settings ()
 382   (setq nsm-permanent-host-settings
 383         (with-temp-buffer
 384           (insert-file-contents nsm-settings-file)
 385           (goto-char (point-min))
 386           (ignore-errors (read (current-buffer))))))
 387
 388 (defun nsm-id (host port)
 389   (concat "sha1:" (sha1 (format "%s:%s" host port))))
 390
 391 (defun nsm-host-settings (id)
 392   (when (and (not nsm-permanent-host-settings)
 393              (file-exists-p nsm-settings-file))
 394     (nsm-read-settings))
 395   (let ((result nil))
 396     (dolist (elem (append nsm-temporary-host-settings
 397                           nsm-permanent-host-settings))
 398       (when (and (not result)
 399                  (equal (plist-get elem :id) id))
 400         (setq result elem)))
 401     result))
 402
 403 (defun nsm-warnings-ok-p (status settings)
 404   (let ((ok t)
 405         (conditions (plist-get settings :conditions)))
 406     (dolist (warning (plist-get status :warnings))
 407       (unless (memq warning conditions)
 408         (setq ok nil)))
 409     ok))
 410
 411 (defun nsm-remove-permanent-setting (id)
 412   (setq nsm-permanent-host-settings
 413         (cl-delete-if
 414          (lambda (elem)
 415            (equal (plist-get elem :id) id))
 416          nsm-permanent-host-settings)))
 417
 418 (defun nsm-remove-temporary-setting (id)
 419   (setq nsm-temporary-host-settings
 420         (cl-delete-if
 421          (lambda (elem)
 422            (equal (plist-get elem :id) id))
 423          nsm-temporary-host-settings)))
 424
 425 (defun nsm-format-certificate (status)
 426   (let ((cert (plist-get status :certificate)))
 427     (when cert
 428       (with-temp-buffer
 429         (insert
 430          "Certificate information\n"
 431          "Issued by:"
 432          (nsm-certificate-part (plist-get cert :issuer) "CN" t) "\n"
 433          "Issued to:"
 434          (or (nsm-certificate-part (plist-get cert :subject) "O")
 435              (nsm-certificate-part (plist-get cert :subject) "OU" t))
 436          "\n"
 437          "Hostname:"
 438          (nsm-certificate-part (plist-get cert :subject) "CN" t) "\n")
 439         (when (and (plist-get cert :public-key-algorithm)
 440                    (plist-get cert :signature-algorithm))
 441           (insert
 442            "Public key:" (plist-get cert :public-key-algorithm)
 443            ", signature: " (plist-get cert :signature-algorithm) "\n"))
 444         (when (and (plist-get status :key-exchange)
 445                    (plist-get status :cipher)
 446                    (plist-get status :mac)
 447                    (plist-get status :protocol))
 448           (insert
 449            "Protocol:" (plist-get status :protocol)
 450            ", key: " (plist-get status :key-exchange)
 451            ", cipher: " (plist-get status :cipher)
 452            ", mac: " (plist-get status :mac) "\n"))
 453         (when (plist-get cert :certificate-security-level)
 454           (insert
 455            "Security level:"
 456            (propertize (plist-get cert :certificate-security-level)
 457                        'face 'bold)
 458            "\n"))
 459         (insert
 460          "Valid:From " (plist-get cert :valid-from)
 461          " to " (plist-get cert :valid-to) "\n\n")
 462         (goto-char (point-min))
 463         (while (re-search-forward "^[^:]+:" nil t)
 464           (insert (make-string (- 20 (current-column)) ? )))
 465         (buffer-string)))))
 466
 467 (defun nsm-certificate-part (string part &optional full)
 468   (let ((part (cadr (assoc part (nsm-parse-subject string)))))
 469     (cond
 470      (part part)
 471      (full string)
 472      (t nil))))
 473
 474 (defun nsm-parse-subject (string)
 475   (with-temp-buffer
 476     (insert string)
 477     (goto-char (point-min))
 478     (let ((start (point))
 479           (result nil))
 480       (while (not (eobp))
 481         (push (replace-regexp-in-string
 482                "[\\]\\(.\\)" "\\1"
 483                (buffer-substring start
 484                                  (if (re-search-forward "[^\\]," nil 'move)
 485                                      (1- (point))
 486                                    (point))))
 487               result)
 488         (setq start (point)))
 489       (mapcar
 490        (lambda (elem)
 491          (let ((pos (cl-position ?= elem)))
 492            (if pos
 493                (list (substring elem 0 pos)
 494                      (substring elem (1+ pos)))
 495              elem)))
 496        (nreverse result)))))
 497
 498 (defun nsm-level (symbol)
 499   "Return a numerical level for SYMBOL for easier comparison."
 500   (cond
 501    ((eq symbol 'low) 0)
 502    ((eq symbol 'medium) 1)
 503    ((eq symbol 'high) 2)
 504    (t 3)))
 505
 506 (provide 'nsm)
 507
 508 ;;; nsm.el ends here