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