core: New function gpgme_op_revsig.

* src/gpgme.h.in (gpgme_op_revsig_start, gpgme_op_revsig): New.
(GPGME_REVSIG_LFSEP): New.
* src/context.h (ctx_op_data_id_t): Add OPDATA_REVSIG.
* src/revsig.c: New.
* src/Makefile.am (main_sources): Add revsig.
* src/libgpgme.vers, src/gpgme.def: Add gpgme_op_revsig and
gpgme_op_revsig_start.
* src/engine.h, src/engine.c: (_gpgme_engine_op_revsig): New.
* src/engine-backend.h (engine_ops): Add 'revsig' and adjust all
engine initializers.
* src/engine-gpg.c (gpg_revsig): New.
(_gpgme_engine_ops_gpg): Set revsig to gpg_revsig.
* doc/gpgme.texi: Document new functions.
* tests/run-keysign.c: Add option --revoke.
--

This extends GPGME to support the --quick-revoke-sig command
added by GnuPG 2.2.24. This allows revoking key signatures.

GnuPG-bug-id: 5094

NEWS

@@ -1,8 +1,11 @@
 Noteworthy changes in version 1.14.1 (unreleased)
 -------------------------------------------------
 
-* New function gpgme_op_setexpire to make changing the expiration
+ * New function gpgme_op_setexpire to make changing the expiration
-  easier (requires GnuPG 2.1.22). [#4999]
+   easier (requires GnuPG 2.1.22). [#4999]
+
+ * New function gpgme_op_revsig to revoke key signatures (requires
+   GnuPG 2.2.24). [#5094]
 
  * cpp: Support for set expire operations in the C++ bindings. [#5003]
 
@@ -15,6 +18,9 @@ Noteworthy changes in version 1.14.1 (unreleased)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  gpgme_op_setexpire_start                   NEW.
  gpgme_op_setexpire                         NEW.
+ gpgme_op_revsig_start                      NEW.
+ gpgme_op_revsig                            NEW.
+ GPGME_REVSIG_LFSEP                         NEW.
  cpp: Context::setExpire                    NEW.
  cpp: Context::startSetExpire               NEW.
  cpp: EngineInfo::Version::operator<=       NEW.

doc/gpgme.texi

@@ -4725,6 +4725,71 @@ be completed by calling @code{gpgme_wait} on the context.
 @end deftypefun
 
 
+@c
+@c  gpgme_op_revsig
+@c
+@deftypefun gpgme_error_t gpgme_op_revsig @
+      (@w{gpgme_ctx_t @var{ctx}}, @
+       @w{gpgme_key_t @var{key}}, @
+       @w{gpgme_key_t @var{signing_key}}, @
+       @w{const char *@var{userid}}, @
+       @w{unsigned int @var{flags}});
+
+@since{1.14.1}
+
+The function @code{gpgme_op_revsig} revokes key signatures of the
+public key @var{key} made with the key @var{signing_key}.   This
+function requires at least version 2.2.24 of GnuPG.
+
+@var{key} specifies the key to operate on.
+
+@var{signing_key} specifies the key whose signatures shall be revoked.
+
+@var{userid} selects the user ID or user IDs whose signatures shall
+be revoked.  If @var{userid} is set to @code{NULL} the signatures
+on all user IDs are revoked.  The user ID must be given verbatim
+because the engine does an exact and case sensitive match.  Thus the
+@code{uid} field from the user ID object (@code{gpgme_user_id_t}) is to
+be used.  To select more than one user ID put them all into one string
+separated by linefeeds characters (@code{\n}) and set the flag
+@code{GPGME_REVSIG_LFSEP}.
+
+@var{flags} can be set to the bit-wise OR of the following flags:
+
+@table @code
+@item GPGME_REVSIG_LFSEP
+@since{1.14.1}
+
+Although linefeeds are uncommon in user IDs this flag is required to
+explicitly declare that @var{userid} may contain several linefeed
+separated user IDs.
+
+@end table
+
+The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
+the engine does not support the command, or a bunch of other error
+codes.
+
+@end deftypefun
+
+
+@deftypefun gpgme_error_t gpgme_op_revsig_start @
+      (@w{gpgme_ctx_t @var{ctx}}, @
+       @w{gpgme_key_t @var{key}}, @
+       @w{gpgme_key_t @var{signing_key}}, @
+       @w{const char *@var{userid}}, @
+       @w{unsigned int @var{flags}});
+
+@since{1.14.1}
+
+The function @code{gpgme_op_revsig_start} initiates a
+@code{gpgme_op_revsig} operation; see there for details.  It must
+be completed by calling @code{gpgme_wait} on the context.
+@xref{Waiting For Completion}.
+
+@end deftypefun
+
+
 @c
 @c  EXPORTING KEYS
 @c

src/Makefile.am

@@ -79,6 +79,7 @@ main_sources =								\
 	encrypt.c encrypt-sign.c decrypt.c decrypt-verify.c verify.c	\
 	sign.c passphrase.c progress.c					\
 	key.c keylist.c keysign.c trust-item.c trustlist.c tofupolicy.c	\
+	revsig.c							\
 	import.c export.c genkey.c delete.c edit.c getauditlog.c        \
 	setexpire.c							\
 	opassuan.c passwd.c spawn.c assuan-support.c                    \

src/context.h

@@ -39,7 +39,7 @@ typedef enum
     OPDATA_IMPORT, OPDATA_GENKEY, OPDATA_KEYLIST, OPDATA_EDIT,
     OPDATA_VERIFY, OPDATA_TRUSTLIST, OPDATA_ASSUAN, OPDATA_VFS_MOUNT,
     OPDATA_PASSWD, OPDATA_EXPORT, OPDATA_KEYSIGN, OPDATA_TOFU_POLICY,
-    OPDATA_QUERY_SWDB, OPDATA_SETEXPIRE
+    OPDATA_QUERY_SWDB, OPDATA_SETEXPIRE, OPDATA_REVSIG
   } ctx_op_data_id_t;
 
 

src/engine-assuan.c

@@ -833,6 +833,7 @@ struct engine_ops _gpgme_engine_ops_assuan =
     NULL,               /* keylist_ext */
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     NULL,               /* sign */
     NULL,               /* verify */

src/engine-backend.h

@@ -108,6 +108,9 @@ struct engine_ops
                             gpgme_key_t key, const char *userid,
                             unsigned long expires, unsigned int flags,
                             gpgme_ctx_t ctx);
+  gpgme_error_t (*revsig) (void *engine,
+                           gpgme_key_t key, gpgme_key_t signing_key,
+                           const char *userid, unsigned int flags);
   gpgme_error_t (*tofu_policy) (void *engine,
                                 gpgme_key_t key,
                                 gpgme_tofu_policy_t policy);

src/engine-g13.c

@@ -804,6 +804,7 @@ struct engine_ops _gpgme_engine_ops_g13 =
     NULL,               /* keylist_ext */
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     NULL,               /* sign */
     NULL,               /* verify */

src/engine-gpg.c

@@ -3210,6 +3210,52 @@ gpg_keysign (void *engine, gpgme_key_t key, const char *userid,
 }
 
 
+static gpgme_error_t
+gpg_revsig (void *engine, gpgme_key_t key, gpgme_key_t signing_key,
+            const char *userid, unsigned int flags)
+{
+  engine_gpg_t gpg = engine;
+  gpgme_error_t err;
+  const char *s;
+
+  if (!key || !key->fpr)
+    return gpg_error (GPG_ERR_INV_ARG);
+
+  if (!have_gpg_version (gpg, "2.2.24"))
+    return gpg_error (GPG_ERR_NOT_SUPPORTED);
+
+  err = add_arg (gpg, "--quick-revoke-sig");
+
+  if (!err)
+    err = add_arg (gpg, "--");
+
+  if (!err)
+    err = add_arg (gpg, key->fpr);
+
+  if (!err)
+    err = add_arg (gpg, signing_key->fpr);
+
+  if (!err && userid)
+    {
+      if ((flags & GPGME_REVSIG_LFSEP))
+        {
+          for (; !err && (s = strchr (userid, '\n')); userid = s + 1)
+            if ((s - userid))
+              err = add_arg_len (gpg, "=", userid, s - userid);
+          if (!err && *userid)
+            err = add_arg_pfx (gpg, "=", userid);
+        }
+      else
+        err = add_arg_pfx (gpg, "=", userid);
+    }
+
+  if (!err)
+    err = start (gpg);
+
+  return err;
+}
+
+
 static gpgme_error_t
 gpg_tofu_policy (void *engine, gpgme_key_t key, gpgme_tofu_policy_t policy)
 {
@@ -3513,6 +3559,7 @@ struct engine_ops _gpgme_engine_ops_gpg =
     gpg_keylist_ext,
     gpg_keylist_data,
     gpg_keysign,
+    gpg_revsig,
     gpg_tofu_policy,    /* tofu_policy */
     gpg_sign,
     gpg_verify,

src/engine-gpgconf.c

@@ -1302,6 +1302,7 @@ struct engine_ops _gpgme_engine_ops_gpgconf =
     NULL,		/* keylist_ext */
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     NULL,		/* sign */
     NULL,		/* verify */

src/engine-gpgsm.c

@@ -2322,6 +2322,7 @@ struct engine_ops _gpgme_engine_ops_gpgsm =
     gpgsm_keylist_ext,
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     gpgsm_sign,
     gpgsm_verify,

src/engine-spawn.c

@@ -464,6 +464,7 @@ struct engine_ops _gpgme_engine_ops_spawn =
     NULL,		/* keylist_ext */
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     NULL,		/* sign */
     NULL,		/* verify */

src/engine-uiserver.c

@@ -1435,6 +1435,7 @@ struct engine_ops _gpgme_engine_ops_uiserver =
     NULL,		/* keylist_ext */
     NULL,               /* keylist_data */
     NULL,               /* keysign */
+    NULL,               /* revsig */
     NULL,               /* tofu_policy */
     uiserver_sign,
     uiserver_verify,

src/engine.c

@@ -824,6 +824,20 @@ _gpgme_engine_op_keysign (engine_t engine, gpgme_key_t key, const char *userid,
 }
 
 
+gpgme_error_t
+_gpgme_engine_op_revsig (engine_t engine, gpgme_key_t key, gpgme_key_t signing_key,
+                         const char *userid, unsigned int flags)
+{
+  if (!engine)
+    return gpg_error (GPG_ERR_INV_VALUE);
+
+  if (!engine->ops->revsig)
+    return gpg_error (GPG_ERR_NOT_IMPLEMENTED);
+
+  return (*engine->ops->revsig) (engine->engine, key, signing_key, userid, flags);
+}
+
+
 gpgme_error_t
 _gpgme_engine_op_tofu_policy (engine_t engine,
                               gpgme_key_t key,  gpgme_tofu_policy_t policy)

src/engine.h

@@ -131,6 +131,11 @@ gpgme_error_t _gpgme_engine_op_keysign (engine_t engine,
                                         unsigned long expires,
                                         unsigned int flags,
                                         gpgme_ctx_t ctx);
+gpgme_error_t _gpgme_engine_op_revsig (engine_t engine,
+                                       gpgme_key_t key,
+                                       gpgme_key_t signing_key,
+                                       const char *userid,
+                                       unsigned int flags);
 gpgme_error_t _gpgme_engine_op_tofu_policy (engine_t engine,
                                             gpgme_key_t key,
                                             gpgme_tofu_policy_t policy);

src/gpgme.def

@@ -277,5 +277,8 @@ EXPORTS
     gpgme_op_setexpire                    @205
     gpgme_op_setexpire_start              @206
 
+    gpgme_op_revsig                       @207
+    gpgme_op_revsig_start                 @208
+
 ; END
 

src/gpgme.h.in

@@ -1919,6 +1919,20 @@ gpgme_error_t gpgme_op_keysign       (gpgme_ctx_t ctx,
                                       unsigned int flags);
 
 
+/* Flags for the signature revoking functions.  */
+#define GPGME_REVSIG_LFSEP   (1 << 8)  /* Indicate LF separated user ids. */
+
+/* Revoke the signatures made with SIGNING_KEY on the USERID(s) of KEY.  */
+gpgme_error_t gpgme_op_revsig_start (gpgme_ctx_t ctx,
+                                     gpgme_key_t key,
+                                     gpgme_key_t signing_key,
+                                     const char *userid,
+                                     unsigned int flags);
+gpgme_error_t gpgme_op_revsig       (gpgme_ctx_t ctx,
+                                     gpgme_key_t key,
+                                     gpgme_key_t signing_key,
+                                     const char *userid,
+                                     unsigned int flags);
 
 
 /*

src/libgpgme.vers

@@ -276,6 +276,9 @@ GPGME_1.0 {
     gpgme_op_setexpire;
     gpgme_op_setexpire_start;
 
+    gpgme_op_revsig;
+    gpgme_op_revsig_start;
+
   local:
     *;
 

src/revsig.c

@@ -0,0 +1,203 @@
+/* revsig.c - Revoke signature helpers.
+ * Copyright (C) 2020 g10 Code GmbH
+ *
+ * This file is part of GPGME.
+ *
+ * GPGME is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * GPGME is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, see <https://gnu.org/licenses/>.
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#if HAVE_CONFIG_H
+#include <config.h>
+#endif
+#include <stdlib.h>
+
+#include "gpgme.h"
+#include "debug.h"
+#include "context.h"
+#include "ops.h"
+
+
+typedef struct
+{
+  /* The error code from a FAILURE status line or 0.  */
+  gpg_error_t failure_code;
+
+  /* The error code from certain ERROR status lines or 0.  */
+  gpg_error_t error_code;
+
+} *op_data_t;
+
+
+/* Parse an error status line.  Return the error location and the
+   error code.  The function may modify ARGS. */
+static char *
+parse_error (char *args, gpg_error_t *r_err)
+{
+  char *where = strchr (args, ' ');
+  char *which;
+
+  if (where)
+    {
+      *where = '\0';
+      which = where + 1;
+
+      where = strchr (which, ' ');
+      if (where)
+	*where = '\0';
+
+      where = args;
+    }
+  else
+    {
+      *r_err = trace_gpg_error (GPG_ERR_INV_ENGINE);
+      return NULL;
+    }
+
+  *r_err = atoi (which);
+
+  return where;
+}
+
+
+static gpgme_error_t
+revsig_status_handler (void *priv, gpgme_status_code_t code, char *args)
+{
+  gpgme_ctx_t ctx = (gpgme_ctx_t) priv;
+  gpgme_error_t err;
+  void *hook;
+  op_data_t opd;
+  char *loc;
+
+  /* Pipe the status code through the progress status handler.  */
+  err = _gpgme_progress_status_handler (ctx, code, args);
+  if (err)
+    return err;
+
+  err = _gpgme_op_data_lookup (ctx, OPDATA_REVSIG, &hook, -1, NULL);
+  opd = hook;
+  if (err)
+    return err;
+
+  switch (code)
+    {
+    case GPGME_STATUS_ERROR:
+      loc = parse_error (args, &err);
+      if (!loc)
+        return err;
+      if (!opd->error_code)
+        opd->error_code = err;
+      break;
+
+    case GPGME_STATUS_FAILURE:
+      opd->failure_code = _gpgme_parse_failure (args);
+      break;
+
+    case GPGME_STATUS_EOF:
+      if (opd->error_code)
+        return opd->error_code;
+      else if (opd->failure_code)
+        return opd->failure_code;
+      break;
+
+    case GPGME_STATUS_INQUIRE_MAXLEN:
+      if (ctx->status_cb && !ctx->full_status)
+        {
+          err = ctx->status_cb (ctx->status_cb_value, "INQUIRE_MAXLEN", args);
+          if (err)
+            return err;
+        }
+      break;
+
+    default:
+      break;
+    }
+  return 0;
+}
+
+
+/* Revoke the signature(s) on USERID of KEY made with SIGNING_KEY.
+ * If USERID is NULL, revoke signatures on all user ids.  To put several
+ * user ids into USERID, separate them by LF and set the flag
+ * GPGME_REVSIG_LFSEP.  */
+static gpgme_error_t
+revsig_start (gpgme_ctx_t ctx, int synchronous,
+              gpgme_key_t key, gpgme_key_t signing_key,
+              const char *userid, unsigned int flags)
+{
+  gpgme_error_t err;
+  void *hook;
+  op_data_t opd;
+
+  if (!ctx)
+    return gpg_error (GPG_ERR_INV_ARG);
+
+  if (ctx->protocol != GPGME_PROTOCOL_OPENPGP)
+    return gpgme_error (GPG_ERR_UNSUPPORTED_PROTOCOL);
+
+  if (!key)
+    return gpg_error (GPG_ERR_INV_ARG);
+
+  err = _gpgme_op_reset (ctx, synchronous);
+  if (err)
+    return err;
+
+  err = _gpgme_op_data_lookup (ctx, OPDATA_REVSIG, &hook, sizeof (*opd),
+                               NULL);
+  opd = hook;
+  if (err)
+    return err;
+
+  _gpgme_engine_set_status_handler (ctx->engine, revsig_status_handler, ctx);
+
+  if (ctx->passphrase_cb)
+    {
+      err = _gpgme_engine_set_command_handler
+        (ctx->engine, _gpgme_passphrase_command_handler, ctx);
+      if (err)
+        return err;
+    }
+
+  return _gpgme_engine_op_revsig (ctx->engine, key, signing_key, userid, flags);
+}
+
+
+gpgme_error_t
+gpgme_op_revsig_start (gpgme_ctx_t ctx, gpgme_key_t key, gpgme_key_t signing_key,
+                       const char *userid, unsigned int flags)
+{
+  gpgme_error_t err;
+
+  TRACE_BEG  (DEBUG_CTX, "gpgme_op_revsig_start", ctx,
+	      "key=%p, uid='%s' flags=0x%x", key, userid, flags);
+
+  err = revsig_start (ctx, 0, key, signing_key, userid, flags);
+  return TRACE_ERR (err);
+}
+
+
+gpgme_error_t
+gpgme_op_revsig (gpgme_ctx_t ctx, gpgme_key_t key, gpgme_key_t signing_key,
+                 const char *userid, unsigned int flags)
+{
+  gpgme_error_t err;
+
+  TRACE_BEG  (DEBUG_CTX, "gpgme_op_revsig", ctx,
+	      "key=%p, uid='%s' flags=0x%x", key, userid, flags);
+
+  err = revsig_start (ctx, 1, key, signing_key, userid, flags);
+  if (!err)
+    err = _gpgme_wait_one (ctx);
+  return TRACE_ERR (err);
+}

tests/run-keysign.c

@@ -1,4 +1,4 @@
-/* run-keysign.c  - Test tool to sign a key
+/* run-keysign.c  - Test tool to sign a key and to revoke a key signature
  * Copyright (C) 2016 g10 Code GmbH
  *
  * This file is part of GPGME.
@@ -77,10 +77,11 @@ show_usage (int ex)
          "  --verbose        run in verbose mode\n"
          "  --status         print status lines from the backend\n"
          "  --loopback       use a loopback pinentry\n"
-         "  --signer NAME    use key NAME for signing\n"
+         "  --signer NAME    use key NAME for signing/revoking\n"
          "  --local          create a local signature\n"
          "  --noexpire       force no expiration\n"
          "  --expire EPOCH   expire the signature at EPOCH\n"
+         "  --revoke         revoke the signature(s)\n"
          , stderr);
   exit (ex);
 }
@@ -97,9 +98,12 @@ main (int argc, char **argv)
   int print_status = 0;
   int use_loopback = 0;
   const char *userid;
-  unsigned int flags = 0;
+  unsigned int keysign_flags = 0;
   unsigned long expire = 0;
+  int revoke = 0;
+  unsigned int revoke_flags = 0;
   gpgme_key_t thekey;
+  gpgme_key_t signing_key = NULL;
   int i;
   size_t n;
   char *userid_buffer = NULL;
@@ -142,12 +146,12 @@ main (int argc, char **argv)
         }
       else if (!strcmp (*argv, "--local"))
         {
-          flags |= GPGME_KEYSIGN_LOCAL;
+          keysign_flags |= GPGME_KEYSIGN_LOCAL;
           argc--; argv++;
         }
       else if (!strcmp (*argv, "--noexpire"))
         {
-          flags |= GPGME_KEYSIGN_NOEXPIRE;
+          keysign_flags |= GPGME_KEYSIGN_NOEXPIRE;
           argc--; argv++;
         }
       else if (!strcmp (*argv, "--expire"))
@@ -158,10 +162,21 @@ main (int argc, char **argv)
           expire = parse_expire_string (*argv);
           argc--; argv++;
         }
+      else if (!strcmp (*argv, "--revoke"))
+        {
+          revoke = 1;
+          argc--; argv++;
+        }
       else if (!strncmp (*argv, "--", 2))
         show_usage (1);
     }
 
+  if (revoke && !signer_string)
+    {
+      fprintf (stderr, PGM ": please specify the signer key\n");
+      exit (1);
+    }
+
   if (!argc)
     show_usage (1);
   userid = argv[0];
@@ -186,23 +201,20 @@ main (int argc, char **argv)
 
   if (signer_string)
     {
-      gpgme_key_t akey;
+      err = gpgme_get_key (ctx, signer_string, &signing_key, 1);
-
-      err = gpgme_get_key (ctx, signer_string, &akey, 1);
       if (err)
         {
           fprintf (stderr, PGM ": error getting signer key '%s': %s\n",
                    signer_string, gpg_strerror (err));
           exit (1);
         }
-      err = gpgme_signers_add (ctx, akey);
+      err = gpgme_signers_add (ctx, signing_key);
       if (err)
         {
           fprintf (stderr, PGM ": error adding signer key: %s\n",
                    gpg_strerror (err));
           exit (1);
         }
-      gpgme_key_unref (akey);
     }
 
 
@@ -234,7 +246,8 @@ main (int argc, char **argv)
           strcat (userid_buffer, "\n");
         }
       userid = userid_buffer;
-      flags |= GPGME_KEYSIGN_LFSEP;
+      keysign_flags |= GPGME_KEYSIGN_LFSEP;
+      revoke_flags |= GPGME_REVSIG_LFSEP;
     }
   else if (argc)
     {
@@ -247,15 +260,29 @@ main (int argc, char **argv)
       userid = NULL;
     }
 
-  err = gpgme_op_keysign (ctx, thekey, userid, expire, flags);
+  if (revoke)
-  if (err)
     {
-      fprintf (stderr, PGM ": gpgme_op_adduid failed: %s\n",
+      err = gpgme_op_revsig (ctx, thekey, signing_key, userid, revoke_flags);
-               gpg_strerror (err));
+      if (err)
-      exit (1);
+        {
+          fprintf (stderr, PGM ": gpgme_op_revsig failed: %s\n",
+                   gpg_strerror (err));
+          exit (1);
+        }
+    }
+  else
+    {
+      err = gpgme_op_keysign (ctx, thekey, userid, expire, keysign_flags);
+      if (err)
+        {
+          fprintf (stderr, PGM ": gpgme_op_keysign failed: %s\n",
+                   gpg_strerror (err));
+          exit (1);
+        }
     }
 
   free (userid_buffer);
+  gpgme_key_unref (signing_key);
   gpgme_key_unref (thekey);
   gpgme_release (ctx);
   return 0;