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   1 ;;; mml-smime.el --- S/MIME support for MML
   2
   3 ;; Copyright (C) 2000, 2001, 2002, 2003, 2004,
   4 ;;   2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
   5
   6 ;; Author: Simon Josefsson <simon@josefsson.org>
   7 ;; Keywords: Gnus, MIME, S/MIME, MML
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;;; Code:
  27
  28 ;; For Emacs < 22.2.
  29 (eval-and-compile
  30   (unless (fboundp 'declare-function) (defmacro declare-function (&rest r))))
  31
  32 (eval-when-compile (require 'cl))
  33
  34 (require 'smime)
  35 (require 'mm-decode)
  36 (require 'mml-sec)
  37 (autoload 'message-narrow-to-headers "message")
  38 (autoload 'message-fetch-field "message")
  39
  40 (defvar mml-smime-use 'openssl)
  41
  42 (defvar mml-smime-function-alist
  43   '((openssl mml-smime-openssl-sign
  44              mml-smime-openssl-encrypt
  45              mml-smime-openssl-sign-query
  46              mml-smime-openssl-encrypt-query
  47              mml-smime-openssl-verify
  48              mml-smime-openssl-verify-test)
  49     (epg mml-smime-epg-sign
  50          mml-smime-epg-encrypt
  51          nil
  52          nil
  53          mml-smime-epg-verify
  54          mml-smime-epg-verify-test)))
  55
  56 (defcustom mml-smime-verbose mml-secure-verbose
  57   "If non-nil, ask the user about the current operation more verbosely."
  58   :group 'mime-security
  59   :type 'boolean)
  60
  61 (defcustom mml-smime-cache-passphrase mml-secure-cache-passphrase
  62   "If t, cache passphrase."
  63   :group 'mime-security
  64   :type 'boolean)
  65
  66 (defcustom mml-smime-passphrase-cache-expiry mml-secure-passphrase-cache-expiry
  67   "How many seconds the passphrase is cached.
  68 Whether the passphrase is cached at all is controlled by
  69 `mml-smime-cache-passphrase'."
  70   :group 'mime-security
  71   :type 'integer)
  72
  73 (defcustom mml-smime-signers nil
  74   "A list of your own key ID which will be used to sign a message."
  75   :group 'mime-security
  76   :type '(repeat (string :tag "Key ID")))
  77
  78 (defun mml-smime-sign (cont)
  79   (let ((func (nth 1 (assq mml-smime-use mml-smime-function-alist))))
  80     (if func
  81         (funcall func cont)
  82       (error "Cannot find sign function"))))
  83
  84 (defun mml-smime-encrypt (cont)
  85   (let ((func (nth 2 (assq mml-smime-use mml-smime-function-alist))))
  86     (if func
  87         (funcall func cont)
  88       (error "Cannot find encrypt function"))))
  89
  90 (defun mml-smime-sign-query ()
  91   (let ((func (nth 3 (assq mml-smime-use mml-smime-function-alist))))
  92     (if func
  93         (funcall func))))
  94
  95 (defun mml-smime-encrypt-query ()
  96   (let ((func (nth 4 (assq mml-smime-use mml-smime-function-alist))))
  97     (if func
  98         (funcall func))))
  99
 100 (defun mml-smime-verify (handle ctl)
 101   (let ((func (nth 5 (assq mml-smime-use mml-smime-function-alist))))
 102     (if func
 103         (funcall func handle ctl)
 104       handle)))
 105
 106 (defun mml-smime-verify-test (handle ctl)
 107   (let ((func (nth 6 (assq mml-smime-use mml-smime-function-alist))))
 108     (if func
 109         (funcall func handle ctl))))
 110
 111 (defun mml-smime-openssl-sign (cont)
 112   (when (null smime-keys)
 113     (customize-variable 'smime-keys)
 114     (error "No S/MIME keys configured, use customize to add your key"))
 115   (smime-sign-buffer (cdr (assq 'keyfile cont)))
 116   (goto-char (point-min))
 117   (while (search-forward "\r\n" nil t)
 118     (replace-match "\n" t t))
 119   (goto-char (point-max)))
 120
 121 (defun mml-smime-openssl-encrypt (cont)
 122   (let (certnames certfiles tmp file tmpfiles)
 123     ;; xxx tmp files are always an security issue
 124     (while (setq tmp (pop cont))
 125       (if (and (consp tmp) (eq (car tmp) 'certfile))
 126           (push (cdr tmp) certnames)))
 127     (while (setq tmp (pop certnames))
 128       (if (not (and (not (file-exists-p tmp))
 129                     (get-buffer tmp)))
 130           (push tmp certfiles)
 131         (setq file (mm-make-temp-file (expand-file-name "mml."
 132                                                         mm-tmp-directory)))
 133         (with-current-buffer tmp
 134           (write-region (point-min) (point-max) file))
 135         (push file certfiles)
 136         (push file tmpfiles)))
 137     (if (smime-encrypt-buffer certfiles)
 138         (progn
 139           (while (setq tmp (pop tmpfiles))
 140             (delete-file tmp))
 141           t)
 142       (while (setq tmp (pop tmpfiles))
 143         (delete-file tmp))
 144       nil))
 145   (goto-char (point-max)))
 146
 147 (defvar gnus-extract-address-components)
 148
 149 (defun mml-smime-openssl-sign-query ()
 150   ;; query information (what certificate) from user when MML tag is
 151   ;; added, for use later by the signing process
 152   (when (null smime-keys)
 153     (customize-variable 'smime-keys)
 154     (error "No S/MIME keys configured, use customize to add your key"))
 155   (list 'keyfile
 156         (if (= (length smime-keys) 1)
 157             (cadar smime-keys)
 158           (or (let ((from (cadr (funcall (if (boundp
 159                                               'gnus-extract-address-components)
 160                                              gnus-extract-address-components
 161                                            'mail-extract-address-components)
 162                                          (or (save-excursion
 163                                                (save-restriction
 164                                                  (message-narrow-to-headers)
 165                                                  (message-fetch-field "from")))
 166                                              "")))))
 167                 (and from (smime-get-key-by-email from)))
 168               (smime-get-key-by-email
 169                (completing-read "Sign this part with what signature? "
 170                                 smime-keys nil nil
 171                                 (and (listp (car-safe smime-keys))
 172                                      (caar smime-keys))))))))
 173
 174 (defun mml-smime-get-file-cert ()
 175   (ignore-errors
 176     (list 'certfile (read-file-name
 177                      "File with recipient's S/MIME certificate: "
 178                      smime-certificate-directory nil t ""))))
 179
 180 (defun mml-smime-get-dns-cert ()
 181   ;; todo: deal with comma separated multiple recipients
 182   (let (result who bad cert)
 183     (condition-case ()
 184         (while (not result)
 185           (setq who (read-from-minibuffer
 186                      (format "%sLookup certificate for: " (or bad ""))
 187                      (cadr (funcall (if (boundp
 188                                          'gnus-extract-address-components)
 189                                         gnus-extract-address-components
 190                                       'mail-extract-address-components)
 191                                     (or (save-excursion
 192                                           (save-restriction
 193                                             (message-narrow-to-headers)
 194                                             (message-fetch-field "to")))
 195                                         "")))))
 196           (if (setq cert (smime-cert-by-dns who))
 197               (setq result (list 'certfile (buffer-name cert)))
 198             (setq bad (format "`%s' not found. " who))))
 199       (quit))
 200     result))
 201
 202 (defun mml-smime-get-ldap-cert ()
 203   ;; todo: deal with comma separated multiple recipients
 204   (let (result who bad cert)
 205     (condition-case ()
 206         (while (not result)
 207           (setq who (read-from-minibuffer
 208                      (format "%sLookup certificate for: " (or bad ""))
 209                      (cadr (funcall gnus-extract-address-components
 210                                     (or (save-excursion
 211                                           (save-restriction
 212                                             (message-narrow-to-headers)
 213                                             (message-fetch-field "to")))
 214                                         "")))))
 215           (if (setq cert (smime-cert-by-ldap who))
 216               (setq result (list 'certfile (buffer-name cert)))
 217             (setq bad (format "`%s' not found. " who))))
 218       (quit))
 219     result))
 220
 221 (autoload 'gnus-completing-read-with-default "gnus-util")
 222
 223 (defun mml-smime-openssl-encrypt-query ()
 224   ;; todo: try dns/ldap automatically first, before prompting user
 225   (let (certs done)
 226     (while (not done)
 227       (ecase (read (gnus-completing-read-with-default
 228                     "ldap" "Fetch certificate from"
 229                     '(("dns") ("ldap") ("file")) nil t))
 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 (mm-find-part-by-type
 524                                        (cdr handle)
 525                                        "application/pkcs7-signature"
 526                                        nil t))))
 527         (mm-set-handle-multipart-parameter
 528          mm-security-handle 'gnus-info "Corrupted")
 529         (throw 'error handle))
 530       (setq part (mm-replace-in-string part "\n" "\r\n" t)
 531             context (epg-make-context 'CMS))
 532       (condition-case error
 533           (setq plain (epg-verify-string context (mm-get-part signature) part))
 534         (error
 535          (mm-set-handle-multipart-parameter
 536           mm-security-handle 'gnus-info "Failed")
 537          (if (eq (car error) 'quit)
 538              (mm-set-handle-multipart-parameter
 539               mm-security-handle 'gnus-details "Quit.")
 540            (mm-set-handle-multipart-parameter
 541             mm-security-handle 'gnus-details (format "%S" error)))
 542          (throw 'error handle)))
 543       (mm-set-handle-multipart-parameter
 544        mm-security-handle 'gnus-info
 545        (epg-verify-result-to-string (epg-context-result-for context 'verify)))
 546       handle)))
 547
 548 (defun mml-smime-epg-verify-test (handle ctl)
 549   t)
 550
 551 (provide 'mml-smime)
 552
 553 ;; arch-tag: f1bf94d4-f2cd-4c6f-b059-ad69492817e2
 554 ;;; mml-smime.el ends here