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   1 ;;; mml-smime.el --- S/MIME support for MML
   2
   3 ;; Copyright (C) 2000-2012 Free Software Foundation, Inc.
   4
   5 ;; Author: Simon Josefsson <simon@josefsson.org>
   6 ;; Keywords: Gnus, MIME, S/MIME, MML
   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 ;; For Emacs <22.2 and XEmacs.
  28 (eval-and-compile
  29   (unless (fboundp 'declare-function) (defmacro declare-function (&rest r))))
  30
  31 (eval-when-compile (require 'cl))
  32
  33 (require 'smime)
  34 (require 'mm-decode)
  35 (require 'mml-sec)
  36 (autoload 'message-narrow-to-headers "message")
  37 (autoload 'message-fetch-field "message")
  38
  39 (defcustom mml-smime-use (if (featurep 'epg) 'epg 'openssl)
  40   "Whether to use OpenSSL or EPG to decrypt S/MIME messages.
  41 Defaults to EPG if it's loaded."
  42   :group 'mime-security
  43   :type '(choice (const :tag "EPG" epg)
  44                  (const :tag "OpenSSL" openssl)))
  45
  46 (defvar mml-smime-function-alist
  47   '((openssl mml-smime-openssl-sign
  48              mml-smime-openssl-encrypt
  49              mml-smime-openssl-sign-query
  50              mml-smime-openssl-encrypt-query
  51              mml-smime-openssl-verify
  52              mml-smime-openssl-verify-test)
  53     (epg mml-smime-epg-sign
  54          mml-smime-epg-encrypt
  55          nil
  56          nil
  57          mml-smime-epg-verify
  58          mml-smime-epg-verify-test)))
  59
  60 (defcustom mml-smime-cache-passphrase mml-secure-cache-passphrase
  61   "If t, cache passphrase."
  62   :group 'mime-security
  63   :type 'boolean)
  64
  65 (defcustom mml-smime-passphrase-cache-expiry mml-secure-passphrase-cache-expiry
  66   "How many seconds the passphrase is cached.
  67 Whether the passphrase is cached at all is controlled by
  68 `mml-smime-cache-passphrase'."
  69   :group 'mime-security
  70   :type 'integer)
  71
  72 (defcustom mml-smime-signers nil
  73   "A list of your own key ID which will be used to sign a message."
  74   :group 'mime-security
  75   :type '(repeat (string :tag "Key ID")))
  76
  77 (defun mml-smime-sign (cont)
  78   (let ((func (nth 1 (assq mml-smime-use mml-smime-function-alist))))
  79     (if func
  80         (funcall func cont)
  81       (error "Cannot find sign function"))))
  82
  83 (defun mml-smime-encrypt (cont)
  84   (let ((func (nth 2 (assq mml-smime-use mml-smime-function-alist))))
  85     (if func
  86         (funcall func cont)
  87       (error "Cannot find encrypt function"))))
  88
  89 (defun mml-smime-sign-query ()
  90   (let ((func (nth 3 (assq mml-smime-use mml-smime-function-alist))))
  91     (if func
  92         (funcall func))))
  93
  94 (defun mml-smime-encrypt-query ()
  95   (let ((func (nth 4 (assq mml-smime-use mml-smime-function-alist))))
  96     (if func
  97         (funcall func))))
  98
  99 (defun mml-smime-verify (handle ctl)
 100   (let ((func (nth 5 (assq mml-smime-use mml-smime-function-alist))))
 101     (if func
 102         (funcall func handle ctl)
 103       handle)))
 104
 105 (defun mml-smime-verify-test (handle ctl)
 106   (let ((func (nth 6 (assq mml-smime-use mml-smime-function-alist))))
 107     (if func
 108         (funcall func handle ctl))))
 109
 110 (defun mml-smime-openssl-sign (cont)
 111   (when (null smime-keys)
 112     (customize-variable 'smime-keys)
 113     (error "No S/MIME keys configured, use customize to add your key"))
 114   (smime-sign-buffer (cdr (assq 'keyfile cont)))
 115   (goto-char (point-min))
 116   (while (search-forward "\r\n" nil t)
 117     (replace-match "\n" t t))
 118   (goto-char (point-max)))
 119
 120 (defun mml-smime-openssl-encrypt (cont)
 121   (let (certnames certfiles tmp file tmpfiles)
 122     ;; xxx tmp files are always an security issue
 123     (while (setq tmp (pop cont))
 124       (if (and (consp tmp) (eq (car tmp) 'certfile))
 125           (push (cdr tmp) certnames)))
 126     (while (setq tmp (pop certnames))
 127       (if (not (and (not (file-exists-p tmp))
 128                     (get-buffer tmp)))
 129           (push tmp certfiles)
 130         (setq file (mm-make-temp-file (expand-file-name "mml."
 131                                                         mm-tmp-directory)))
 132         (with-current-buffer tmp
 133           (write-region (point-min) (point-max) file))
 134         (push file certfiles)
 135         (push file tmpfiles)))
 136     (if (smime-encrypt-buffer certfiles)
 137         (progn
 138           (while (setq tmp (pop tmpfiles))
 139             (delete-file tmp))
 140           t)
 141       (while (setq tmp (pop tmpfiles))
 142         (delete-file tmp))
 143       nil))
 144   (goto-char (point-max)))
 145
 146 (defvar gnus-extract-address-components)
 147
 148 (defun mml-smime-openssl-sign-query ()
 149   ;; query information (what certificate) from user when MML tag is
 150   ;; added, for use later by the signing process
 151   (when (null smime-keys)
 152     (customize-variable 'smime-keys)
 153     (error "No S/MIME keys configured, use customize to add your key"))
 154   (list 'keyfile
 155         (if (= (length smime-keys) 1)
 156             (cadar smime-keys)
 157           (or (let ((from (cadr (funcall (if (boundp
 158                                               'gnus-extract-address-components)
 159                                              gnus-extract-address-components
 160                                            'mail-extract-address-components)
 161                                          (or (save-excursion
 162                                                (save-restriction
 163                                                  (message-narrow-to-headers)
 164                                                  (message-fetch-field "from")))
 165                                              "")))))
 166                 (and from (smime-get-key-by-email from)))
 167               (smime-get-key-by-email
 168                (gnus-completing-read "Sign this part with what signature"
 169                                      (mapcar 'car smime-keys) nil nil nil
 170                                      (and (listp (car-safe smime-keys))
 171                                           (caar smime-keys))))))))
 172
 173 (defun mml-smime-get-file-cert ()
 174   (ignore-errors
 175     (list 'certfile (read-file-name
 176                      "File with recipient's S/MIME certificate: "
 177                      smime-certificate-directory nil t ""))))
 178
 179 (defun mml-smime-get-dns-cert ()
 180   ;; todo: deal with comma separated multiple recipients
 181   (let (result who bad cert)
 182     (condition-case ()
 183         (while (not result)
 184           (setq who (read-from-minibuffer
 185                      (format "%sLookup certificate for: " (or bad ""))
 186                      (cadr (funcall (if (boundp
 187                                          'gnus-extract-address-components)
 188                                         gnus-extract-address-components
 189                                       'mail-extract-address-components)
 190                                     (or (save-excursion
 191                                           (save-restriction
 192                                             (message-narrow-to-headers)
 193                                             (message-fetch-field "to")))
 194                                         "")))))
 195           (if (setq cert (smime-cert-by-dns who))
 196               (setq result (list 'certfile (buffer-name cert)))
 197             (setq bad (format "`%s' not found. " who))))
 198       (quit))
 199     result))
 200
 201 (defun mml-smime-get-ldap-cert ()
 202   ;; todo: deal with comma separated multiple recipients
 203   (let (result who bad cert)
 204     (condition-case ()
 205         (while (not result)
 206           (setq who (read-from-minibuffer
 207                      (format "%sLookup certificate for: " (or bad ""))
 208                      (cadr (funcall gnus-extract-address-components
 209                                     (or (save-excursion
 210                                           (save-restriction
 211                                             (message-narrow-to-headers)
 212                                             (message-fetch-field "to")))
 213                                         "")))))
 214           (if (setq cert (smime-cert-by-ldap who))
 215               (setq result (list 'certfile (buffer-name cert)))
 216             (setq bad (format "`%s' not found. " who))))
 217       (quit))
 218     result))
 219
 220 (autoload 'gnus-completing-read "gnus-util")
 221
 222 (defun mml-smime-openssl-encrypt-query ()
 223   ;; todo: try dns/ldap automatically first, before prompting user
 224   (let (certs done)
 225     (while (not done)
 226       (ecase (read (gnus-completing-read
 227                     "Fetch certificate from"
 228                     '("dns" "ldap" "file") t nil nil
 229                     "ldap"))
 230         (dns (setq certs (append certs
 231                                  (mml-smime-get-dns-cert))))
 232         (ldap (setq certs (append certs
 233                                   (mml-smime-get-ldap-cert))))
 234         (file (setq certs (append certs
 235                                   (mml-smime-get-file-cert)))))
 236       (setq done (not (y-or-n-p "Add more recipients? "))))
 237     certs))
 238
 239 (defun mml-smime-openssl-verify (handle ctl)
 240   (with-temp-buffer
 241     (insert-buffer-substring (mm-handle-multipart-original-buffer ctl))
 242     (goto-char (point-min))
 243     (insert (format "Content-Type: %s; " (mm-handle-media-type ctl)))
 244     (insert (format "protocol=\"%s\"; "
 245                     (mm-handle-multipart-ctl-parameter ctl 'protocol)))
 246     (insert (format "micalg=\"%s\"; "
 247                     (mm-handle-multipart-ctl-parameter ctl 'micalg)))
 248     (insert (format "boundary=\"%s\"\n\n"
 249                     (mm-handle-multipart-ctl-parameter ctl 'boundary)))
 250     (when (get-buffer smime-details-buffer)
 251       (kill-buffer smime-details-buffer))
 252     (let ((buf (current-buffer))
 253           (good-signature (smime-noverify-buffer))
 254           (good-certificate (and (or smime-CA-file smime-CA-directory)
 255                                  (smime-verify-buffer)))
 256           addresses openssl-output)
 257       (setq openssl-output (with-current-buffer smime-details-buffer
 258                              (buffer-string)))
 259       (if (not good-signature)
 260           (progn
 261             ;; we couldn't verify message, fail with openssl output as message
 262             (mm-set-handle-multipart-parameter
 263              mm-security-handle 'gnus-info "Failed")
 264             (mm-set-handle-multipart-parameter
 265              mm-security-handle 'gnus-details
 266              (concat "OpenSSL failed to verify message integrity:\n"
 267                      "-------------------------------------------\n"
 268                      openssl-output)))
 269         ;; verify mail addresses in mail against those in certificate
 270         (when (and (smime-pkcs7-region (point-min) (point-max))
 271                    (smime-pkcs7-certificates-region (point-min) (point-max)))
 272           (with-temp-buffer
 273             (insert-buffer-substring buf)
 274             (goto-char (point-min))
 275             (while (re-search-forward "-----END CERTIFICATE-----" nil t)
 276               (when (smime-pkcs7-email-region (point-min) (point))
 277                 (setq addresses (append (smime-buffer-as-string-region
 278                                          (point-min) (point)) addresses)))
 279               (delete-region (point-min) (point)))
 280             (setq addresses (mapcar 'downcase addresses))))
 281         (if (not (member (downcase (or (mm-handle-multipart-from ctl) "")) addresses))
 282             (mm-set-handle-multipart-parameter
 283              mm-security-handle 'gnus-info "Sender address forged")
 284           (if good-certificate
 285               (mm-set-handle-multipart-parameter
 286                mm-security-handle 'gnus-info "Ok (sender authenticated)")
 287             (mm-set-handle-multipart-parameter
 288              mm-security-handle 'gnus-info "Ok (sender not trusted)")))
 289         (mm-set-handle-multipart-parameter
 290          mm-security-handle 'gnus-details
 291          (concat "Sender claimed to be: " (mm-handle-multipart-from ctl) "\n"
 292                  (if addresses
 293                      (concat "Addresses in certificate: "
 294                              (mapconcat 'identity addresses ", "))
 295                    "No addresses found in certificate. (Requires OpenSSL 0.9.6 or later.)")
 296                  "\n" "\n"
 297                  "OpenSSL output:\n"
 298                  "---------------\n" openssl-output "\n"
 299                  "Certificate(s) inside S/MIME signature:\n"
 300                  "---------------------------------------\n"
 301                  (buffer-string) "\n")))))
 302   handle)
 303
 304 (defun mml-smime-openssl-verify-test (handle ctl)
 305   smime-openssl-program)
 306
 307 (defvar epg-user-id-alist)
 308 (defvar epg-digest-algorithm-alist)
 309 (defvar inhibit-redisplay)
 310 (defvar password-cache-expiry)
 311
 312 (eval-when-compile
 313   (autoload 'epg-make-context "epg")
 314   (autoload 'epg-context-set-armor "epg")
 315   (autoload 'epg-context-set-signers "epg")
 316   (autoload 'epg-context-result-for "epg")
 317   (autoload 'epg-new-signature-digest-algorithm "epg")
 318   (autoload 'epg-verify-result-to-string "epg")
 319   (autoload 'epg-list-keys "epg")
 320   (autoload 'epg-decrypt-string "epg")
 321   (autoload 'epg-verify-string "epg")
 322   (autoload 'epg-sign-string "epg")
 323   (autoload 'epg-encrypt-string "epg")
 324   (autoload 'epg-passphrase-callback-function "epg")
 325   (autoload 'epg-context-set-passphrase-callback "epg")
 326   (autoload 'epg-configuration "epg-config")
 327   (autoload 'epg-expand-group "epg-config")
 328   (autoload 'epa-select-keys "epa"))
 329
 330 (defvar mml-smime-epg-secret-key-id-list nil)
 331
 332 (defun mml-smime-epg-passphrase-callback (context key-id ignore)
 333   (if (eq key-id 'SYM)
 334       (epg-passphrase-callback-function context key-id nil)
 335     (let* (entry
 336            (passphrase
 337             (password-read
 338              (if (eq key-id 'PIN)
 339                  "Passphrase for PIN: "
 340                (if (setq entry (assoc key-id epg-user-id-alist))
 341                    (format "Passphrase for %s %s: " key-id (cdr entry))
 342                  (format "Passphrase for %s: " key-id)))
 343              (if (eq key-id 'PIN)
 344                  "PIN"
 345                key-id))))
 346       (when passphrase
 347         (let ((password-cache-expiry mml-smime-passphrase-cache-expiry))
 348           (password-cache-add key-id passphrase))
 349         (setq mml-smime-epg-secret-key-id-list
 350               (cons key-id mml-smime-epg-secret-key-id-list))
 351         (copy-sequence passphrase)))))
 352
 353 (declare-function epg-key-sub-key-list   "ext:epg" (key))
 354 (declare-function epg-sub-key-capability "ext:epg" (sub-key))
 355 (declare-function epg-sub-key-validity   "ext:epg" (sub-key))
 356
 357 (defun mml-smime-epg-find-usable-key (keys usage)
 358   (catch 'found
 359     (while keys
 360       (let ((pointer (epg-key-sub-key-list (car keys))))
 361         (while pointer
 362           (if (and (memq usage (epg-sub-key-capability (car pointer)))
 363                    (not (memq (epg-sub-key-validity (car pointer))
 364                               '(revoked expired))))
 365               (throw 'found (car keys)))
 366           (setq pointer (cdr pointer))))
 367       (setq keys (cdr keys)))))
 368
 369 (autoload 'mml-compute-boundary "mml")
 370
 371 ;; We require mm-decode, which requires mm-bodies, which autoloads
 372 ;; message-options-get (!).
 373 (declare-function message-options-set "message" (symbol value))
 374
 375 (defun mml-smime-epg-sign (cont)
 376   (let* ((inhibit-redisplay t)
 377          (context (epg-make-context 'CMS))
 378          (boundary (mml-compute-boundary cont))
 379          signer-key
 380          (signers
 381           (or (message-options-get 'mml-smime-epg-signers)
 382               (message-options-set
 383               'mml-smime-epg-signers
 384               (if (eq mm-sign-option 'guided)
 385                   (epa-select-keys context "\
 386 Select keys for signing.
 387 If no one is selected, default secret key is used.  "
 388                                    mml-smime-signers t)
 389                 (if mml-smime-signers
 390                     (mapcar
 391                      (lambda (signer)
 392                        (setq signer-key (mml-smime-epg-find-usable-key
 393                                          (epg-list-keys context signer t)
 394                                          'sign))
 395                        (unless (or signer-key
 396                                    (y-or-n-p
 397                                     (format "No secret key for %s; skip it? "
 398                                             signer)))
 399                          (error "No secret key for %s" signer))
 400                        signer-key)
 401                      mml-smime-signers))))))
 402          signature micalg)
 403     (epg-context-set-signers context signers)
 404     (if mml-smime-cache-passphrase
 405         (epg-context-set-passphrase-callback
 406          context
 407          #'mml-smime-epg-passphrase-callback))
 408     (condition-case error
 409         (setq signature (epg-sign-string context
 410                                          (mm-replace-in-string (buffer-string)
 411                                                                "\n" "\r\n")
 412                                          t)
 413               mml-smime-epg-secret-key-id-list nil)
 414       (error
 415        (while mml-smime-epg-secret-key-id-list
 416          (password-cache-remove (car mml-smime-epg-secret-key-id-list))
 417          (setq mml-smime-epg-secret-key-id-list
 418                (cdr mml-smime-epg-secret-key-id-list)))
 419        (signal (car error) (cdr error))))
 420     (if (epg-context-result-for context 'sign)
 421         (setq micalg (epg-new-signature-digest-algorithm
 422                       (car (epg-context-result-for context 'sign)))))
 423     (goto-char (point-min))
 424     (insert (format "Content-Type: multipart/signed; boundary=\"%s\";\n"
 425                     boundary))
 426     (if micalg
 427         (insert (format "\tmicalg=%s; "
 428                         (downcase
 429                          (cdr (assq micalg
 430                                     epg-digest-algorithm-alist))))))
 431     (insert "protocol=\"application/pkcs7-signature\"\n")
 432     (insert (format "\n--%s\n" boundary))
 433     (goto-char (point-max))
 434     (insert (format "\n--%s\n" boundary))
 435     (insert "Content-Type: application/pkcs7-signature; name=smime.p7s
 436 Content-Transfer-Encoding: base64
 437 Content-Disposition: attachment; filename=smime.p7s
 438
 439 ")
 440     (insert (base64-encode-string signature) "\n")
 441     (goto-char (point-max))
 442     (insert (format "--%s--\n" boundary))
 443     (goto-char (point-max))))
 444
 445 (defun mml-smime-epg-encrypt (cont)
 446   (let ((inhibit-redisplay t)
 447         (context (epg-make-context 'CMS))
 448         (config (epg-configuration))
 449         (recipients (message-options-get 'mml-smime-epg-recipients))
 450         cipher signers
 451         (boundary (mml-compute-boundary cont))
 452         recipient-key)
 453     (unless recipients
 454       (setq recipients
 455             (apply #'nconc
 456                    (mapcar
 457                     (lambda (recipient)
 458                       (or (epg-expand-group config recipient)
 459                           (list recipient)))
 460                     (split-string
 461                      (or (message-options-get 'message-recipients)
 462                          (message-options-set 'message-recipients
 463                                               (read-string "Recipients: ")))
 464                      "[ \f\t\n\r\v,]+"))))
 465       (if (eq mm-encrypt-option 'guided)
 466           (setq recipients
 467                 (epa-select-keys context "\
 468 Select recipients for encryption.
 469 If no one is selected, symmetric encryption will be performed.  "
 470                                  recipients))
 471         (setq recipients
 472               (mapcar
 473                (lambda (recipient)
 474                  (setq recipient-key (mml-smime-epg-find-usable-key
 475                                       (epg-list-keys context recipient)
 476                                       'encrypt))
 477                  (unless (or recipient-key
 478                              (y-or-n-p
 479                               (format "No public key for %s; skip it? "
 480                                       recipient)))
 481                    (error "No public key for %s" recipient))
 482                  recipient-key)
 483                recipients))
 484         (unless recipients
 485           (error "No recipient specified")))
 486       (message-options-set 'mml-smime-epg-recipients recipients))
 487     (if mml-smime-cache-passphrase
 488         (epg-context-set-passphrase-callback
 489          context
 490          #'mml-smime-epg-passphrase-callback))
 491     (condition-case error
 492         (setq cipher
 493               (epg-encrypt-string context (buffer-string) recipients)
 494               mml-smime-epg-secret-key-id-list nil)
 495       (error
 496        (while mml-smime-epg-secret-key-id-list
 497          (password-cache-remove (car mml-smime-epg-secret-key-id-list))
 498          (setq mml-smime-epg-secret-key-id-list
 499                (cdr mml-smime-epg-secret-key-id-list)))
 500        (signal (car error) (cdr error))))
 501     (delete-region (point-min) (point-max))
 502     (goto-char (point-min))
 503     (insert "\
 504 Content-Type: application/pkcs7-mime;
 505  smime-type=enveloped-data;
 506  name=smime.p7m
 507 Content-Transfer-Encoding: base64
 508 Content-Disposition: attachment; filename=smime.p7m
 509
 510 ")
 511     (insert (base64-encode-string cipher))
 512     (goto-char (point-max))))
 513
 514 (defun mml-smime-epg-verify (handle ctl)
 515   (catch 'error
 516     (let ((inhibit-redisplay t)
 517           context plain signature-file part signature)
 518       (when (or (null (setq part (mm-find-raw-part-by-type
 519                                   ctl (or (mm-handle-multipart-ctl-parameter
 520                                            ctl 'protocol)
 521                                           "application/pkcs7-signature")
 522                                   t)))
 523                 (null (setq signature (or (mm-find-part-by-type
 524                                            (cdr handle)
 525                                            "application/pkcs7-signature"
 526                                            nil t)
 527                                           (mm-find-part-by-type
 528                                            (cdr handle)
 529                                            "application/x-pkcs7-signature"
 530                                            nil t)))))
 531         (mm-set-handle-multipart-parameter
 532          mm-security-handle 'gnus-info "Corrupted")
 533         (throw 'error handle))
 534       (setq part (mm-replace-in-string part "\n" "\r\n")
 535             context (epg-make-context 'CMS))
 536       (condition-case error
 537           (setq plain (epg-verify-string context (mm-get-part signature) part))
 538         (error
 539          (mm-set-handle-multipart-parameter
 540           mm-security-handle 'gnus-info "Failed")
 541          (if (eq (car error) 'quit)
 542              (mm-set-handle-multipart-parameter
 543               mm-security-handle 'gnus-details "Quit.")
 544            (mm-set-handle-multipart-parameter
 545             mm-security-handle 'gnus-details (format "%S" error)))
 546          (throw 'error handle)))
 547       (mm-set-handle-multipart-parameter
 548        mm-security-handle 'gnus-info
 549        (epg-verify-result-to-string (epg-context-result-for context 'verify)))
 550       handle)))
 551
 552 (defun mml-smime-epg-verify-test (handle ctl)
 553   t)
 554
 555 (provide 'mml-smime)
 556
 557 ;;; mml-smime.el ends here