g10/call-agent.c

   1 /* call-agent.c - divert operations to the agent
   2  * Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <config.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <errno.h>
  25 #include <unistd.h>
  26 #include <time.h>
  27 #include <assert.h>
  28 #ifdef HAVE_LOCALE_H
  29 #include <locale.h>
  30 #endif
  31 #include <assuan.h>
  32
  33 #include "gpg.h"
  34 #include "util.h"
  35 #include "membuf.h"
  36 #include "options.h"
  37 #include "i18n.h"
  38 #include "asshelp.h"
  39 #include "call-agent.h"
  40
  41 #ifndef DBG_ASSUAN
  42 # define DBG_ASSUAN 1
  43 #endif
  44
  45 static assuan_context_t agent_ctx = NULL;
  46
  47 struct cipher_parm_s
  48 {
  49   assuan_context_t ctx;
  50   const char *ciphertext;
  51   size_t ciphertextlen;
  52 };
  53
  54 struct writekey_parm_s
  55 {
  56   assuan_context_t ctx;
  57   const unsigned char *keydata;
  58   size_t keydatalen;
  59 };
  60
  61 struct genkey_parm_s
  62 {
  63   assuan_context_t ctx;
  64   const char *sexp;
  65   size_t sexplen;
  66 };
  67
  68
  69 \f
  70 /* Try to connect to the agent via socket or fork it off and work by
  71    pipes.  Handle the server's initial greeting */
  72 static int
  73 start_agent (void)
  74 {
  75   if (agent_ctx)
  76     return 0; /* Fixme: We need a context for each thread or serialize
  77                  the access to the agent. */
  78
  79   return start_new_gpg_agent (&agent_ctx,
  80                               GPG_ERR_SOURCE_DEFAULT,
  81                               opt.homedir,
  82                               opt.agent_program,
  83                               opt.display, opt.ttyname, opt.ttytype,
  84                               opt.lc_ctype, opt.lc_messages,
  85                               opt.verbose, DBG_ASSUAN,
  86                               NULL, NULL);
  87 }
  88
  89
  90 /* Return a new malloced string by unescaping the string S.  Escaping
  91    is percent escaping and '+'/space mapping.  A binary nul will
  92    silently be replaced by a 0xFF.  Function returns NULL to indicate
  93    an out of memory status. */
  94 static char *
  95 unescape_status_string (const unsigned char *s)
  96 {
  97   char *buffer, *d;
  98
  99   buffer = d = xtrymalloc (strlen (s)+1);
 100   if (!buffer)
 101     return NULL;
 102   while (*s)
 103     {
 104       if (*s == '%' && s[1] && s[2])
 105         {
 106           s++;
 107           *d = xtoi_2 (s);
 108           if (!*d)
 109             *d = '\xff';
 110           d++;
 111           s += 2;
 112         }
 113       else if (*s == '+')
 114         {
 115           *d++ = ' ';
 116           s++;
 117         }
 118       else
 119         *d++ = *s++;
 120     }
 121   *d = 0;
 122   return buffer;
 123 }
 124
 125 /* Copy the text ATEXT into the buffer P and do plus '+' and percent
 126    escaping.  Note that the provided buffer needs to be 3 times the
 127    size of ATEXT plus 1.  Returns a pointer to the leading Nul in P. */
 128 static char *
 129 percent_plus_escape (char *p, const char *atext)
 130 {
 131   const unsigned char *s;
 132
 133   for (s=atext; *s; s++)
 134     {
 135       if (*s < ' ' || *s == '+')
 136         {
 137           sprintf (p, "%%%02X", *s);
 138           p += 3;
 139         }
 140       else if (*s == ' ')
 141         *p++ = '+';
 142       else
 143         *p++ = *s;
 144     }
 145   *p = 0;
 146   return p;
 147 }
 148
 149 /* Take a 20 byte hexencoded string and put it into the the provided
 150    20 byte buffer FPR in binary format. */
 151 static int
 152 unhexify_fpr (const char *hexstr, unsigned char *fpr)
 153 {
 154   const char *s;
 155   int n;
 156
 157   for (s=hexstr, n=0; hexdigitp (s); s++, n++)
 158     ;
 159   if (*s || (n != 40))
 160     return 0; /* no fingerprint (invalid or wrong length). */
 161   n /= 2;
 162   for (s=hexstr, n=0; *s; s += 2, n++)
 163     fpr[n] = xtoi_2 (s);
 164   return 1; /* okay */
 165 }
 166
 167 /* Take the serial number from LINE and return it verbatim in a newly
 168    allocated string.  We make sure that only hex characters are
 169    returned. */
 170 static char *
 171 store_serialno (const char *line)
 172 {
 173   const char *s;
 174   char *p;
 175
 176   for (s=line; hexdigitp (s); s++)
 177     ;
 178   p = xtrymalloc (s + 1 - line);
 179   if (p)
 180     {
 181       memcpy (p, line, s-line);
 182       p[s-line] = 0;
 183     }
 184   return p;
 185 }
 186
 187
 188 \f
 189 /* Release the card info structure INFO. */
 190 void
 191 agent_release_card_info (struct agent_card_info_s *info)
 192 {
 193   if (!info)
 194     return;
 195
 196   xfree (info->serialno); info->serialno = NULL;
 197   xfree (info->disp_name); info->disp_name = NULL;
 198   xfree (info->disp_lang); info->disp_lang = NULL;
 199   xfree (info->pubkey_url); info->pubkey_url = NULL;
 200   xfree (info->login_data); info->login_data = NULL;
 201   info->cafpr1valid = info->cafpr2valid = info->cafpr3valid = 0;
 202   info->fpr1valid = info->fpr2valid = info->fpr3valid = 0;
 203 }
 204
 205 static int
 206 learn_status_cb (void *opaque, const char *line)
 207 {
 208   struct agent_card_info_s *parm = opaque;
 209   const char *keyword = line;
 210   int keywordlen;
 211   int i;
 212
 213   for (keywordlen=0; *line && !spacep (line); line++, keywordlen++)
 214     ;
 215   while (spacep (line))
 216     line++;
 217
 218   if (keywordlen == 8 && !memcmp (keyword, "SERIALNO", keywordlen))
 219     {
 220       xfree (parm->serialno);
 221       parm->serialno = store_serialno (line);
 222     }
 223   else if (keywordlen == 9 && !memcmp (keyword, "DISP-NAME", keywordlen))
 224     {
 225       xfree (parm->disp_name);
 226       parm->disp_name = unescape_status_string (line);
 227     }
 228   else if (keywordlen == 9 && !memcmp (keyword, "DISP-LANG", keywordlen))
 229     {
 230       xfree (parm->disp_lang);
 231       parm->disp_lang = unescape_status_string (line);
 232     }
 233   else if (keywordlen == 8 && !memcmp (keyword, "DISP-SEX", keywordlen))
 234     {
 235       parm->disp_sex = *line == '1'? 1 : *line == '2' ? 2: 0;
 236     }
 237   else if (keywordlen == 10 && !memcmp (keyword, "PUBKEY-URL", keywordlen))
 238     {
 239       xfree (parm->pubkey_url);
 240       parm->pubkey_url = unescape_status_string (line);
 241     }
 242   else if (keywordlen == 10 && !memcmp (keyword, "LOGIN-DATA", keywordlen))
 243     {
 244       xfree (parm->login_data);
 245       parm->login_data = unescape_status_string (line);
 246     }
 247   else if (keywordlen == 11 && !memcmp (keyword, "SIG-COUNTER", keywordlen))
 248     {
 249       parm->sig_counter = strtoul (line, NULL, 0);
 250     }
 251   else if (keywordlen == 10 && !memcmp (keyword, "CHV-STATUS", keywordlen))
 252     {
 253       char *p, *buf;
 254
 255       buf = p = unescape_status_string (line);
 256       if (buf)
 257         {
 258           while (spacep (p))
 259             p++;
 260           parm->chv1_cached = atoi (p);
 261           while (*p && !spacep (p))
 262             p++;
 263           while (spacep (p))
 264             p++;
 265           for (i=0; *p && i < 3; i++)
 266             {
 267               parm->chvmaxlen[i] = atoi (p);
 268               while (*p && !spacep (p))
 269                 p++;
 270               while (spacep (p))
 271                 p++;
 272             }
 273           for (i=0; *p && i < 3; i++)
 274             {
 275               parm->chvretry[i] = atoi (p);
 276               while (*p && !spacep (p))
 277                 p++;
 278               while (spacep (p))
 279                 p++;
 280             }
 281           xfree (buf);
 282         }
 283     }
 284   else if (keywordlen == 7 && !memcmp (keyword, "KEY-FPR", keywordlen))
 285     {
 286       int no = atoi (line);
 287       while (*line && !spacep (line))
 288         line++;
 289       while (spacep (line))
 290         line++;
 291       if (no == 1)
 292         parm->fpr1valid = unhexify_fpr (line, parm->fpr1);
 293       else if (no == 2)
 294         parm->fpr2valid = unhexify_fpr (line, parm->fpr2);
 295       else if (no == 3)
 296         parm->fpr3valid = unhexify_fpr (line, parm->fpr3);
 297     }
 298   else if (keywordlen == 6 && !memcmp (keyword, "CA-FPR", keywordlen))
 299     {
 300       int no = atoi (line);
 301       while (*line && !spacep (line))
 302         line++;
 303       while (spacep (line))
 304         line++;
 305       if (no == 1)
 306         parm->cafpr1valid = unhexify_fpr (line, parm->cafpr1);
 307       else if (no == 2)
 308         parm->cafpr2valid = unhexify_fpr (line, parm->cafpr2);
 309       else if (no == 3)
 310         parm->cafpr3valid = unhexify_fpr (line, parm->cafpr3);
 311     }
 312
 313   return 0;
 314 }
 315
 316 /* Call the agent to learn about a smartcard */
 317 int
 318 agent_learn (struct agent_card_info_s *info)
 319 {
 320   int rc;
 321
 322   rc = start_agent ();
 323   if (rc)
 324     return rc;
 325
 326   memset (info, 0, sizeof *info);
 327   rc = assuan_transact (agent_ctx, "LEARN --send",
 328                         NULL, NULL, NULL, NULL,
 329                         learn_status_cb, info);
 330
 331   return rc;
 332 }
 333
 334 /* Call the agent to retrieve a data object.  This function returns
 335    the data in the same structure as used by the learn command.  It is
 336    allowed to update such a structure using this commmand. */
 337 int
 338 agent_scd_getattr (const char *name, struct agent_card_info_s *info)
 339 {
 340   int rc;
 341   char line[ASSUAN_LINELENGTH];
 342
 343   if (!*name)
 344     return gpg_error (GPG_ERR_INV_VALUE);
 345
 346   /* We assume that NAME does not need escaping. */
 347   if (12 + strlen (name) > DIM(line)-1)
 348     return gpg_error (GPG_ERR_TOO_LARGE);
 349   stpcpy (stpcpy (line, "SCD GETATTR "), name);
 350
 351   rc = start_agent ();
 352   if (rc)
 353     return rc;
 354
 355   rc = assuan_transact (agent_ctx, line, NULL, NULL, NULL, NULL,
 356                         learn_status_cb, info);
 357
 358   return rc;
 359 }
 360
 361 \f
 362 /* Send an setattr command to the SCdaemon.  SERIALNO is not actually
 363    used here but required by gpg 1.4's implementation of this code in
 364    cardglue.c. */
 365 int
 366 agent_scd_setattr (const char *name,
 367                    const unsigned char *value, size_t valuelen,
 368                    const char *serialno)
 369 {
 370   int rc;
 371   char line[ASSUAN_LINELENGTH];
 372   char *p;
 373
 374   if (!*name || !valuelen)
 375     return gpg_error (GPG_ERR_INV_VALUE);
 376
 377   /* We assume that NAME does not need escaping. */
 378   if (12 + strlen (name) > DIM(line)-1)
 379     return gpg_error (GPG_ERR_TOO_LARGE);
 380
 381   p = stpcpy (stpcpy (line, "SCD SETATTR "), name);
 382   *p++ = ' ';
 383   for (; valuelen; value++, valuelen--)
 384     {
 385       if (p >= line + DIM(line)-5 )
 386         return gpg_error (GPG_ERR_TOO_LARGE);
 387       if (*value < ' ' || *value == '+' || *value == '%')
 388         {
 389           sprintf (p, "%%%02X", *value);
 390           p += 3;
 391         }
 392       else if (*value == ' ')
 393         *p++ = '+';
 394       else
 395         *p++ = *value;
 396     }
 397   *p = 0;
 398
 399   rc = start_agent ();
 400   if (rc)
 401     return rc;
 402
 403   rc = assuan_transact (agent_ctx, line, NULL, NULL, NULL, NULL, NULL, NULL);
 404   return rc;
 405 }
 406
 407
 408 \f
 409 /* Handle a KEYDATA inquiry.  Note, we only send the data,
 410    assuan_transact takes care of flushing and writing the end */
 411 static assuan_error_t
 412 inq_writekey_parms (void *opaque, const char *keyword)
 413 {
 414   struct writekey_parm_s *parm = opaque;
 415
 416   return assuan_send_data (parm->ctx, parm->keydata, parm->keydatalen);
 417 }
 418
 419
 420 /* Send a WRITEKEY command to the SCdaemon. */
 421 int
 422 agent_scd_writekey (int keyno, const char *serialno,
 423                     const unsigned char *keydata, size_t keydatalen)
 424 {
 425   int rc;
 426   char line[ASSUAN_LINELENGTH];
 427   struct writekey_parm_s parms;
 428
 429   rc = start_agent ();
 430   if (rc)
 431     return rc;
 432
 433   memset (&parms, 0, sizeof parms);
 434
 435   snprintf (line, DIM(line)-1, "SCD WRITEKEY --force OPENPGP.%d", keyno);
 436   line[DIM(line)-1] = 0;
 437   parms.ctx = agent_ctx;
 438   parms.keydata = keydata;
 439   parms.keydatalen = keydatalen;
 440
 441   rc = assuan_transact (agent_ctx, line, NULL, NULL,
 442                         inq_writekey_parms, &parms, NULL, NULL);
 443
 444   return rc;
 445 }
 446
 447
 448
 449 \f
 450 /* Status callback for the SCD GENKEY command. */
 451 static int
 452 scd_genkey_cb (void *opaque, const char *line)
 453 {
 454   struct agent_card_genkey_s *parm = opaque;
 455   const char *keyword = line;
 456   int keywordlen;
 457   gpg_error_t rc;
 458
 459   log_debug ("got status line `%s'\n", line);
 460   for (keywordlen=0; *line && !spacep (line); line++, keywordlen++)
 461     ;
 462   while (spacep (line))
 463     line++;
 464
 465   if (keywordlen == 7 && !memcmp (keyword, "KEY-FPR", keywordlen))
 466     {
 467       parm->fprvalid = unhexify_fpr (line, parm->fpr);
 468     }
 469   if (keywordlen == 8 && !memcmp (keyword, "KEY-DATA", keywordlen))
 470     {
 471       gcry_mpi_t a;
 472       const char *name = line;
 473
 474       while (*line && !spacep (line))
 475         line++;
 476       while (spacep (line))
 477         line++;
 478
 479       rc = gcry_mpi_scan (&a, GCRYMPI_FMT_HEX, line, 0, NULL);
 480       if (rc)
 481         log_error ("error parsing received key data: %s\n", gpg_strerror (rc));
 482       else if (*name == 'n' && spacep (name+1))
 483         parm->n = a;
 484       else if (*name == 'e' && spacep (name+1))
 485         parm->e = a;
 486       else
 487         {
 488           log_info ("unknown parameter name in received key data\n");
 489           gcry_mpi_release (a);
 490         }
 491     }
 492   else if (keywordlen == 14 && !memcmp (keyword,"KEY-CREATED-AT", keywordlen))
 493     {
 494       parm->created_at = (u32)strtoul (line, NULL, 10);
 495     }
 496
 497   return 0;
 498 }
 499
 500 /* Send a GENKEY command to the SCdaemon.  SERIALNO is not used in
 501    this implementation. */
 502 int
 503 agent_scd_genkey (struct agent_card_genkey_s *info, int keyno, int force,
 504                   const char *serialno)
 505 {
 506   int rc;
 507   char line[ASSUAN_LINELENGTH];
 508
 509   rc = start_agent ();
 510   if (rc)
 511     return rc;
 512
 513   memset (info, 0, sizeof *info);
 514   snprintf (line, DIM(line)-1, "SCD GENKEY %s%d",
 515             force? "--force ":"", keyno);
 516   line[DIM(line)-1] = 0;
 517
 518   memset (info, 0, sizeof *info);
 519   rc = assuan_transact (agent_ctx, line,
 520                         NULL, NULL, NULL, NULL,
 521                         scd_genkey_cb, info);
 522
 523   return rc;
 524 }
 525
 526 \f
 527 static int
 528 membuf_data_cb (void *opaque, const void *buffer, size_t length)
 529 {
 530   membuf_t *data = opaque;
 531
 532   if (buffer)
 533     put_membuf (data, buffer, length);
 534   return 0;
 535 }
 536
 537 /* Send a sign command to the scdaemon via gpg-agent's pass thru
 538    mechanism. */
 539 int
 540 agent_scd_pksign (const char *serialno, int hashalgo,
 541                   const unsigned char *indata, size_t indatalen,
 542                   unsigned char **r_buf, size_t *r_buflen)
 543 {
 544   int rc, i;
 545   char *p, line[ASSUAN_LINELENGTH];
 546   membuf_t data;
 547   size_t len;
 548
 549   /* Note, hashalgo is not yet used but hardwired to SHA1 in SCdaemon. */
 550
 551   *r_buf = NULL;
 552   *r_buflen = 0;
 553
 554   rc = start_agent ();
 555   if (rc)
 556     return rc;
 557
 558   if (indatalen*2 + 50 > DIM(line))
 559     return gpg_error (GPG_ERR_GENERAL);
 560
 561   sprintf (line, "SCD SETDATA ");
 562   p = line + strlen (line);
 563   for (i=0; i < indatalen ; i++, p += 2 )
 564     sprintf (p, "%02X", indata[i]);
 565   rc = assuan_transact (agent_ctx, line, NULL, NULL, NULL, NULL, NULL, NULL);
 566   if (rc)
 567     return rc;
 568
 569   init_membuf (&data, 1024);
 570 #if 0
 571   if (!hashalgo) /* Temporary test hack. */
 572     snprintf (line, DIM(line)-1, "SCD PKAUTH %s", serialno);
 573   else
 574 #endif
 575     snprintf (line, DIM(line)-1, "SCD PKSIGN %s%s",
 576               hashalgo == GCRY_MD_RMD160? "--hash=rmd160 " : "",
 577               serialno);
 578   line[DIM(line)-1] = 0;
 579   rc = assuan_transact (agent_ctx, line, membuf_data_cb, &data,
 580                         NULL, NULL, NULL, NULL);
 581   if (rc)
 582     {
 583       xfree (get_membuf (&data, &len));
 584       return rc;
 585     }
 586   *r_buf = get_membuf (&data, r_buflen);
 587
 588   return 0;
 589 }
 590
 591
 592 /* Decrypt INDATA of length INDATALEN using the card identified by
 593    SERIALNO.  Return the plaintext in a nwly allocated buffer stored
 594    at the address of R_BUF.
 595
 596    Note, we currently support only RSA or more exactly algorithms
 597    taking one input data element. */
 598 int
 599 agent_scd_pkdecrypt (const char *serialno,
 600                      const unsigned char *indata, size_t indatalen,
 601                      unsigned char **r_buf, size_t *r_buflen)
 602 {
 603   int rc, i;
 604   char *p, line[ASSUAN_LINELENGTH];
 605   membuf_t data;
 606   size_t len;
 607
 608   *r_buf = NULL;
 609   rc = start_agent ();
 610   if (rc)
 611     return rc;
 612
 613   /* FIXME: use secure memory where appropriate */
 614   if (indatalen*2 + 50 > DIM(line))
 615     return gpg_error (GPG_ERR_GENERAL);
 616
 617   sprintf (line, "SCD SETDATA ");
 618   p = line + strlen (line);
 619   for (i=0; i < indatalen ; i++, p += 2 )
 620     sprintf (p, "%02X", indata[i]);
 621   rc = assuan_transact (agent_ctx, line, NULL, NULL, NULL, NULL, NULL, NULL);
 622   if (rc)
 623     return rc;
 624
 625   init_membuf (&data, 1024);
 626   snprintf (line, DIM(line)-1, "SCD PKDECRYPT %s", serialno);
 627   line[DIM(line)-1] = 0;
 628   rc = assuan_transact (agent_ctx, line,
 629                         membuf_data_cb, &data,
 630                         NULL, NULL, NULL, NULL);
 631   if (rc)
 632     {
 633       xfree (get_membuf (&data, &len));
 634       return rc;
 635     }
 636   *r_buf = get_membuf (&data, r_buflen);
 637   if (!*r_buf)
 638     return gpg_error (GPG_ERR_ENOMEM);
 639
 640   return 0;
 641 }
 642
 643
 644 /* Change the PIN of an OpenPGP card or reset the retry counter.
 645    CHVNO 1: Change the PIN
 646          2: Same as 1
 647          3: Change the admin PIN
 648        101: Set a new PIN and reset the retry counter
 649        102: Same as 101
 650    SERIALNO is not used.
 651  */
 652 int
 653 agent_scd_change_pin (int chvno, const char *serialno)
 654 {
 655   int rc;
 656   char line[ASSUAN_LINELENGTH];
 657   const char *reset = "";
 658
 659   if (chvno >= 100)
 660     reset = "--reset";
 661   chvno %= 100;
 662
 663   rc = start_agent ();
 664   if (rc)
 665     return rc;
 666
 667   snprintf (line, DIM(line)-1, "SCD PASSWD %s %d", reset, chvno);
 668   line[DIM(line)-1] = 0;
 669   rc = assuan_transact (agent_ctx, line, NULL, NULL,
 670                         NULL, NULL, NULL, NULL);
 671   return rc;
 672 }
 673
 674
 675 /* Perform a CHECKPIN operation.  SERIALNO should be the serial
 676    number of the card - optionally followed by the fingerprint;
 677    however the fingerprint is ignored here. */
 678 int
 679 agent_scd_checkpin  (const char *serialno)
 680 {
 681   int rc;
 682   char line[ASSUAN_LINELENGTH];
 683
 684   rc = start_agent ();
 685   if (rc)
 686     return rc;
 687
 688   snprintf (line, DIM(line)-1, "SCD CHECKPIN %s", serialno);
 689   line[DIM(line)-1] = 0;
 690   return assuan_transact (agent_ctx, line,
 691                           NULL, NULL,
 692                           NULL, NULL, NULL, NULL);
 693 }
 694
 695
 696 /* Dummy function, only used by the gpg 1.4 implementation. */
 697 void
 698 agent_clear_pin_cache (const char *sn)
 699 {
 700
 701 }
 702
 703
 704
 705 \f
 706 /* Note: All strings shall be UTF-8. On success the caler needs to
 707    free the string stored at R_PASSPHRASE. On error NULL will be
 708    stored at R_PASSPHRASE and an appropriate fpf error code
 709    returned. */
 710 gpg_error_t
 711 agent_get_passphrase (const char *cache_id,
 712                       const char *err_msg,
 713                       const char *prompt,
 714                       const char *desc_msg,
 715                       char **r_passphrase)
 716 {
 717   int rc;
 718   char *line, *p;
 719   char cmd[] = "GET_PASSPHRASE --data -- ";
 720   membuf_t data;
 721
 722   *r_passphrase = NULL;
 723
 724   rc = start_agent ();
 725   if (rc)
 726     return rc;
 727
 728   /* We allocate 3 times the needed space for the texts so that
 729      there is enough space for escaping. */
 730   line = xtrymalloc ( strlen (cmd) + 1
 731                       + (cache_id? 3*strlen (cache_id): 1) + 1
 732                       + (err_msg?  3*strlen (err_msg): 1) + 1
 733                       + (prompt?   3*strlen (prompt): 1) + 1
 734                       + (desc_msg? 3*strlen (desc_msg): 1) + 1
 735                       + 1);
 736   if (!line)
 737     return gpg_error_from_syserror ();
 738
 739   p = stpcpy (line, cmd);
 740   if (cache_id && *cache_id)
 741     p = percent_plus_escape (p, cache_id);
 742   else
 743     *p++ = 'X';
 744   *p++ = ' ';
 745
 746   if (err_msg && *err_msg)
 747     p = percent_plus_escape (p, err_msg);
 748   else
 749     *p++ = 'X';
 750   *p++ = ' ';
 751
 752   if (prompt && *prompt)
 753     p = percent_plus_escape (p, prompt);
 754   else
 755     *p++ = 'X';
 756   *p++ = ' ';
 757
 758   if (desc_msg && *desc_msg)
 759     p = percent_plus_escape (p, desc_msg);
 760   else
 761     *p++ = 'X';
 762   *p = 0;
 763
 764   init_membuf_secure (&data, 64);
 765   rc = assuan_transact (agent_ctx, line,
 766                         membuf_data_cb, &data, NULL, NULL, NULL, NULL);
 767
 768   if (rc)
 769     xfree (get_membuf (&data, NULL));
 770   else
 771     {
 772       put_membuf (&data, "", 1);
 773       *r_passphrase = get_membuf (&data, NULL);
 774       if (!*r_passphrase)
 775         rc = gpg_error_from_syserror ();
 776     }
 777   xfree (line);
 778   return rc;
 779 }
 780
 781
 782 gpg_error_t
 783 agent_clear_passphrase (const char *cache_id)
 784 {
 785   int rc;
 786   char line[ASSUAN_LINELENGTH];
 787
 788   if (!cache_id || !*cache_id)
 789     return 0;
 790
 791   rc = start_agent ();
 792   if (rc)
 793     return rc;
 794
 795   snprintf (line, DIM(line)-1, "CLEAR_PASSPHRASE %s", cache_id);
 796   line[DIM(line)-1] = 0;
 797   return assuan_transact (agent_ctx, line, NULL, NULL, NULL, NULL, NULL, NULL);
 798 }