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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                (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-with-default "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-with-default
 223                     "ldap" "Fetch certificate from"
 224                     '(("dns") ("ldap") ("file")) nil t))
 225         (dns (setq certs (append certs
 226                                  (mml-smime-get-dns-cert))))
 227         (ldap (setq certs (append certs
 228                                   (mml-smime-get-ldap-cert))))
 229         (file (setq certs (append certs
 230                                   (mml-smime-get-file-cert)))))
 231       (setq done (not (y-or-n-p "Add more recipients? "))))
 232     certs))
 233
 234 (defun mml-smime-openssl-verify (handle ctl)
 235   (with-temp-buffer
 236     (insert-buffer-substring (mm-handle-multipart-original-buffer ctl))
 237     (goto-char (point-min))
 238     (insert (format "Content-Type: %s; " (mm-handle-media-type ctl)))
 239     (insert (format "protocol=\"%s\"; "
 240                     (mm-handle-multipart-ctl-parameter ctl 'protocol)))
 241     (insert (format "micalg=\"%s\"; "
 242                     (mm-handle-multipart-ctl-parameter ctl 'micalg)))
 243     (insert (format "boundary=\"%s\"\n\n"
 244                     (mm-handle-multipart-ctl-parameter ctl 'boundary)))
 245     (when (get-buffer smime-details-buffer)
 246       (kill-buffer smime-details-buffer))
 247     (let ((buf (current-buffer))
 248           (good-signature (smime-noverify-buffer))
 249           (good-certificate (and (or smime-CA-file smime-CA-directory)
 250                                  (smime-verify-buffer)))
 251           addresses openssl-output)
 252       (setq openssl-output (with-current-buffer smime-details-buffer
 253                              (buffer-string)))
 254       (if (not good-signature)
 255           (progn
 256             ;; we couldn't verify message, fail with openssl output as message
 257             (mm-set-handle-multipart-parameter
 258              mm-security-handle 'gnus-info "Failed")
 259             (mm-set-handle-multipart-parameter
 260              mm-security-handle 'gnus-details
 261              (concat "OpenSSL failed to verify message integrity:\n"
 262                      "-------------------------------------------\n"
 263                      openssl-output)))
 264         ;; verify mail addresses in mail against those in certificate
 265         (when (and (smime-pkcs7-region (point-min) (point-max))
 266                    (smime-pkcs7-certificates-region (point-min) (point-max)))
 267           (with-temp-buffer
 268             (insert-buffer-substring buf)
 269             (goto-char (point-min))
 270             (while (re-search-forward "-----END CERTIFICATE-----" nil t)
 271               (when (smime-pkcs7-email-region (point-min) (point))
 272                 (setq addresses (append (smime-buffer-as-string-region
 273                                          (point-min) (point)) addresses)))
 274               (delete-region (point-min) (point)))
 275             (setq addresses (mapcar 'downcase addresses))))
 276         (if (not (member (downcase (or (mm-handle-multipart-from ctl) "")) addresses))
 277             (mm-set-handle-multipart-parameter
 278              mm-security-handle 'gnus-info "Sender address forged")
 279           (if good-certificate
 280               (mm-set-handle-multipart-parameter
 281                mm-security-handle 'gnus-info "Ok (sender authenticated)")
 282             (mm-set-handle-multipart-parameter
 283              mm-security-handle 'gnus-info "Ok (sender not trusted)")))
 284         (mm-set-handle-multipart-parameter
 285          mm-security-handle 'gnus-details
 286          (concat "Sender claimed to be: " (mm-handle-multipart-from ctl) "\n"
 287                  (if addresses
 288                      (concat "Addresses in certificate: "
 289                              (mapconcat 'identity addresses ", "))
 290                    "No addresses found in certificate. (Requires OpenSSL 0.9.6 or later.)")
 291                  "\n" "\n"
 292                  "OpenSSL output:\n"
 293                  "---------------\n" openssl-output "\n"
 294                  "Certificate(s) inside S/MIME signature:\n"
 295                  "---------------------------------------\n"
 296                  (buffer-string) "\n")))))
 297   handle)
 298
 299 (defun mml-smime-openssl-verify-test (handle ctl)
 300   smime-openssl-program)
 301
 302 (defvar epg-user-id-alist)
 303 (defvar epg-digest-algorithm-alist)
 304 (defvar inhibit-redisplay)
 305 (defvar password-cache-expiry)
 306
 307 (eval-when-compile
 308   (autoload 'epg-make-context "epg")
 309   (autoload 'epg-context-set-armor "epg")
 310   (autoload 'epg-context-set-signers "epg")
 311   (autoload 'epg-context-result-for "epg")
 312   (autoload 'epg-new-signature-digest-algorithm "epg")
 313   (autoload 'epg-verify-result-to-string "epg")
 314   (autoload 'epg-list-keys "epg")
 315   (autoload 'epg-decrypt-string "epg")
 316   (autoload 'epg-verify-string "epg")
 317   (autoload 'epg-sign-string "epg")
 318   (autoload 'epg-encrypt-string "epg")
 319   (autoload 'epg-passphrase-callback-function "epg")
 320   (autoload 'epg-context-set-passphrase-callback "epg")
 321   (autoload 'epg-configuration "epg-config")
 322   (autoload 'epg-expand-group "epg-config")
 323   (autoload 'epa-select-keys "epa"))
 324
 325 (defvar mml-smime-epg-secret-key-id-list nil)
 326
 327 (defun mml-smime-epg-passphrase-callback (context key-id ignore)
 328   (if (eq key-id 'SYM)
 329       (epg-passphrase-callback-function context key-id nil)
 330     (let* (entry
 331            (passphrase
 332             (password-read
 333              (if (eq key-id 'PIN)
 334                  "Passphrase for PIN: "
 335                (if (setq entry (assoc key-id epg-user-id-alist))
 336                    (format "Passphrase for %s %s: " key-id (cdr entry))
 337                  (format "Passphrase for %s: " key-id)))
 338              (if (eq key-id 'PIN)
 339                  "PIN"
 340                key-id))))
 341       (when passphrase
 342         (let ((password-cache-expiry mml-smime-passphrase-cache-expiry))
 343           (password-cache-add key-id passphrase))
 344         (setq mml-smime-epg-secret-key-id-list
 345               (cons key-id mml-smime-epg-secret-key-id-list))
 346         (copy-sequence passphrase)))))
 347
 348 (declare-function epg-key-sub-key-list   "ext:epg" (key))
 349 (declare-function epg-sub-key-capability "ext:epg" (sub-key))
 350 (declare-function epg-sub-key-validity   "ext:epg" (sub-key))
 351
 352 (defun mml-smime-epg-find-usable-key (keys usage)
 353   (catch 'found
 354     (while keys
 355       (let ((pointer (epg-key-sub-key-list (car keys))))
 356         (while pointer
 357           (if (and (memq usage (epg-sub-key-capability (car pointer)))
 358                    (not (memq (epg-sub-key-validity (car pointer))
 359                               '(revoked expired))))
 360               (throw 'found (car keys)))
 361           (setq pointer (cdr pointer))))
 362       (setq keys (cdr keys)))))
 363
 364 (autoload 'mml-compute-boundary "mml")
 365
 366 ;; We require mm-decode, which requires mm-bodies, which autoloads
 367 ;; message-options-get (!).
 368 (declare-function message-options-set "message" (symbol value))
 369
 370 (defun mml-smime-epg-sign (cont)
 371   (let* ((inhibit-redisplay t)
 372          (context (epg-make-context 'CMS))
 373          (boundary (mml-compute-boundary cont))
 374          signer-key
 375          (signers
 376           (or (message-options-get 'mml-smime-epg-signers)
 377               (message-options-set
 378               'mml-smime-epg-signers
 379               (if (eq mm-sign-option 'guided)
 380                   (epa-select-keys context "\
 381 Select keys for signing.
 382 If no one is selected, default secret key is used.  "
 383                                    mml-smime-signers t)
 384                 (if mml-smime-signers
 385                     (mapcar
 386                      (lambda (signer)
 387                        (setq signer-key (mml-smime-epg-find-usable-key
 388                                          (epg-list-keys context signer t)
 389                                          'sign))
 390                        (unless (or signer-key
 391                                    (y-or-n-p
 392                                     (format "No secret key for %s; skip it? "
 393                                             signer)))
 394                          (error "No secret key for %s" signer))
 395                        signer-key)
 396                      mml-smime-signers))))))
 397          signature micalg)
 398     (epg-context-set-signers context signers)
 399     (if mml-smime-cache-passphrase
 400         (epg-context-set-passphrase-callback
 401          context
 402          #'mml-smime-epg-passphrase-callback))
 403     (condition-case error
 404         (setq signature (epg-sign-string context
 405                                          (mm-replace-in-string (buffer-string)
 406                                                                "\n" "\r\n")
 407                                          t)
 408               mml-smime-epg-secret-key-id-list nil)
 409       (error
 410        (while mml-smime-epg-secret-key-id-list
 411          (password-cache-remove (car mml-smime-epg-secret-key-id-list))
 412          (setq mml-smime-epg-secret-key-id-list
 413                (cdr mml-smime-epg-secret-key-id-list)))
 414        (signal (car error) (cdr error))))
 415     (if (epg-context-result-for context 'sign)
 416         (setq micalg (epg-new-signature-digest-algorithm
 417                       (car (epg-context-result-for context 'sign)))))
 418     (goto-char (point-min))
 419     (insert (format "Content-Type: multipart/signed; boundary=\"%s\";\n"
 420                     boundary))
 421     (if micalg
 422         (insert (format "\tmicalg=%s; "
 423                         (downcase
 424                          (cdr (assq micalg
 425                                     epg-digest-algorithm-alist))))))
 426     (insert "protocol=\"application/pkcs7-signature\"\n")
 427     (insert (format "\n--%s\n" boundary))
 428     (goto-char (point-max))
 429     (insert (format "\n--%s\n" boundary))
 430     (insert "Content-Type: application/pkcs7-signature; name=smime.p7s
 431 Content-Transfer-Encoding: base64
 432 Content-Disposition: attachment; filename=smime.p7s
 433
 434 ")
 435     (insert (base64-encode-string signature) "\n")
 436     (goto-char (point-max))
 437     (insert (format "--%s--\n" boundary))
 438     (goto-char (point-max))))
 439
 440 (defun mml-smime-epg-encrypt (cont)
 441   (let ((inhibit-redisplay t)
 442         (context (epg-make-context 'CMS))
 443         (config (epg-configuration))
 444         (recipients (message-options-get 'mml-smime-epg-recipients))
 445         cipher signers
 446         (boundary (mml-compute-boundary cont))
 447         recipient-key)
 448     (unless recipients
 449       (setq recipients
 450             (apply #'nconc
 451                    (mapcar
 452                     (lambda (recipient)
 453                       (or (epg-expand-group config recipient)
 454                           (list recipient)))
 455                     (split-string
 456                      (or (message-options-get 'message-recipients)
 457                          (message-options-set 'message-recipients
 458                                               (read-string "Recipients: ")))
 459                      "[ \f\t\n\r\v,]+"))))
 460       (if (eq mm-encrypt-option 'guided)
 461           (setq recipients
 462                 (epa-select-keys context "\
 463 Select recipients for encryption.
 464 If no one is selected, symmetric encryption will be performed.  "
 465                                  recipients))
 466         (setq recipients
 467               (mapcar
 468                (lambda (recipient)
 469                  (setq recipient-key (mml-smime-epg-find-usable-key
 470                                       (epg-list-keys context recipient)
 471                                       'encrypt))
 472                  (unless (or recipient-key
 473                              (y-or-n-p
 474                               (format "No public key for %s; skip it? "
 475                                       recipient)))
 476                    (error "No public key for %s" recipient))
 477                  recipient-key)
 478                recipients))
 479         (unless recipients
 480           (error "No recipient specified")))
 481       (message-options-set 'mml-smime-epg-recipients recipients))
 482     (if mml-smime-cache-passphrase
 483         (epg-context-set-passphrase-callback
 484          context
 485          #'mml-smime-epg-passphrase-callback))
 486     (condition-case error
 487         (setq cipher
 488               (epg-encrypt-string context (buffer-string) recipients)
 489               mml-smime-epg-secret-key-id-list nil)
 490       (error
 491        (while mml-smime-epg-secret-key-id-list
 492          (password-cache-remove (car mml-smime-epg-secret-key-id-list))
 493          (setq mml-smime-epg-secret-key-id-list
 494                (cdr mml-smime-epg-secret-key-id-list)))
 495        (signal (car error) (cdr error))))
 496     (delete-region (point-min) (point-max))
 497     (goto-char (point-min))
 498     (insert "\
 499 Content-Type: application/pkcs7-mime;
 500  smime-type=enveloped-data;
 501  name=smime.p7m
 502 Content-Transfer-Encoding: base64
 503 Content-Disposition: attachment; filename=smime.p7m
 504
 505 ")
 506     (insert (base64-encode-string cipher))
 507     (goto-char (point-max))))
 508
 509 (defun mml-smime-epg-verify (handle ctl)
 510   (catch 'error
 511     (let ((inhibit-redisplay t)
 512           context plain signature-file part signature)
 513       (when (or (null (setq part (mm-find-raw-part-by-type
 514                                   ctl (or (mm-handle-multipart-ctl-parameter
 515                                            ctl 'protocol)
 516                                           "application/pkcs7-signature")
 517                                   t)))
 518                 (null (setq signature (or (mm-find-part-by-type
 519                                            (cdr handle)
 520                                            "application/pkcs7-signature"
 521                                            nil t)
 522                                           (mm-find-part-by-type
 523                                            (cdr handle)
 524                                            "application/x-pkcs7-signature"
 525                                            nil t)))))
 526         (mm-set-handle-multipart-parameter
 527          mm-security-handle 'gnus-info "Corrupted")
 528         (throw 'error handle))
 529       (setq part (mm-replace-in-string part "\n" "\r\n" t)
 530             context (epg-make-context 'CMS))
 531       (condition-case error
 532           (setq plain (epg-verify-string context (mm-get-part signature) part))
 533         (error
 534          (mm-set-handle-multipart-parameter
 535           mm-security-handle 'gnus-info "Failed")
 536          (if (eq (car error) 'quit)
 537              (mm-set-handle-multipart-parameter
 538               mm-security-handle 'gnus-details "Quit.")
 539            (mm-set-handle-multipart-parameter
 540             mm-security-handle 'gnus-details (format "%S" error)))
 541          (throw 'error handle)))
 542       (mm-set-handle-multipart-parameter
 543        mm-security-handle 'gnus-info
 544        (epg-verify-result-to-string (epg-context-result-for context 'verify)))
 545       handle)))
 546
 547 (defun mml-smime-epg-verify-test (handle ctl)
 548   t)
 549
 550 (provide 'mml-smime)
 551
 552 ;;; mml-smime.el ends here