Support a confirm flag for ssh.

This implements the suggestion from bug#1349.  With this change the
fingerprint of the ssh key is also displayed in the pinentry prompts.

NEWS

@@ -5,6 +5,8 @@ Noteworthy changes in version 2.0.18 (unreleased)
 
  * Bug fix for newer versions of Libgcrypt.
 
+ * Support the SSH confirm flag.
+
  * Improved dirmngr/gpgsm interaction for OCSP.
 
 

agent/ChangeLog

@@ -1,3 +1,18 @@
+2011-08-04  Werner Koch  <wk@g10code.com>
+
+	* command-ssh.c (ssh_identity_register): Display the ssh
+	fingerprint in the prompt.
+	(add_control_entry): Add arg FMTFPR and use it as comment in
+	sshcontrol.
+	(confirm_flag_from_sshcontrol): New.
+	(data_sign): Ask for confirmaton if requested.
+	(search_control_file): Add new arg R_CONFIRM and enhance parser.
+	* findkey.c (agent_raw_key_from_file): New.
+	(modify_description): Add format letter %F.
+
+	* findkey.c (agent_key_from_file): Simplify comment extraction by
+	using gcry_sexp_nth_string.
+
 2011-08-04  Werner Koch  <wk@g10code.com>
 
 	* genkey.c (check_passphrase_pattern): Use gpg_strerror.

agent/agent.h

@@ -234,6 +234,8 @@ gpg_error_t agent_key_from_file (ctrl_t ctrl,
                                  cache_mode_t cache_mode,
                                  lookup_ttl_t lookup_ttl,
                                  gcry_sexp_t *result);
+gpg_error_t agent_raw_key_from_file (ctrl_t ctrl, const unsigned char *grip,
+                                     gcry_sexp_t *result);
 gpg_error_t agent_public_key_from_file (ctrl_t ctrl,
                                         const unsigned char *grip,
                                         gcry_sexp_t *result);

agent/command-ssh.c

@@ -34,6 +34,8 @@
 
 #include "estream.h"
 #include "i18n.h"
+#include "../common/ssh-utils.h"
+
 
 
 
@@ -711,18 +713,25 @@ open_control_file (FILE **r_fp, int append)
 /* Search the file at stream FP from the beginning until a matching
    HEXGRIP is found; return success in this case and store true at
    DISABLED if the found key has been disabled.  If R_TTL is not NULL
-   a specified TTL for that key is stored there. */
+   a specified TTL for that key is stored there.  If R_CONFIRM is not
+   NULL it is set to 1 if the key has the confirm flag set. */
 static gpg_error_t
 search_control_file (FILE *fp, const char *hexgrip,
-                     int *r_disabled, int *r_ttl)
+                     int *r_disabled, int *r_ttl, int *r_confirm)
 {
-  int c, i;
+  int c, i, n;
   char *p, *pend, line[256];
   long ttl;
+  int lnr = 0;
+  const char fname[] = "sshcontrol";
 
   assert (strlen (hexgrip) == 40 );
 
-  rewind (fp);
+  if (r_confirm)
+    *r_confirm = 0;
+
+  fseek (fp, 0, SEEK_SET);
+  clearerr (fp);
   *r_disabled = 0;
  next_line:
   do
@@ -733,6 +742,7 @@ search_control_file (FILE *fp, const char *hexgrip,
             return gpg_error (GPG_ERR_EOF);
           return gpg_error (gpg_err_code_from_errno (errno));
         }
+      lnr++;
 
       if (!*line || line[strlen(line)-1] != '\n')
         {
@@ -762,7 +772,7 @@ search_control_file (FILE *fp, const char *hexgrip,
       goto next_line;
   if (i != 40 || !(spacep (p) || *p == '\n'))
     {
-      log_error ("invalid formatted line in ssh control file\n");
+      log_error ("invalid formatted line in `%s', line %d\n", fname, lnr);
       return gpg_error (GPG_ERR_BAD_DATA);
     }
 
@@ -770,13 +780,37 @@ search_control_file (FILE *fp, const char *hexgrip,
   p = pend;
   if (!(spacep (p) || *p == '\n') || ttl < -1)
     {
-      log_error ("invalid TTL value in ssh control file; assuming 0\n");
+      log_error ("invalid TTL value in `%s', line %d; assuming 0\n",
+                 fname, lnr);
       ttl = 0;
     }
   if (r_ttl)
     *r_ttl = ttl;
 
-  /* Here is the place to parse flags if we need them.  */
+  /* Now check for key-value pairs of the form NAME[=VALUE]. */
+  while (*p)
+    {
+      for (; spacep (p) && *p != '\n'; p++)
+        ;
+      if (!*p || *p == '\n')
+        break;
+      n = strcspn (p, "= \t\n");
+      if (p[n] == '=')
+        {
+          log_error ("assigning a value to a flag is not yet supported; "
+                     "in `%s', line %d; flag ignored\n", fname, lnr);
+          p++;
+        }
+      else if (n == 7 && !memcmp (p, "confirm", 7))
+        {
+          if (r_confirm)
+            *r_confirm = 1;
+        }
+      else
+        log_error ("invalid flag `%.*s' in `%s', line %d; ignored\n",
+                   n, p, fname, lnr);
+      p += n;
+    }
 
   return 0; /* Okay:  found it.  */
 }
@@ -785,11 +819,12 @@ search_control_file (FILE *fp, const char *hexgrip,
 
 /* Add an entry to the control file to mark the key with the keygrip
    HEXGRIP as usable for SSH; i.e. it will be returned when ssh asks
-   for it.  This function is in general used to add a key received
+   for it.  FMTFPR is the fingerprint string.  This function is in
-   through the ssh-add function.  We can assume that the user wants to
+   general used to add a key received through the ssh-add function.
-   allow ssh using this key. */
+   We can assume that the user wants to allow ssh using this key. */
 static gpg_error_t
-add_control_entry (ctrl_t ctrl, const char *hexgrip, int ttl)
+add_control_entry (ctrl_t ctrl, const char *hexgrip, const char *fmtfpr,
+                   int ttl, int confirm)
 {
   gpg_error_t err;
   FILE *fp;
@@ -801,7 +836,7 @@ add_control_entry (ctrl_t ctrl, const char *hexgrip, int ttl)
   if (err)
     return err;
 
-  err = search_control_file (fp, hexgrip, &disabled, NULL);
+  err = search_control_file (fp, hexgrip, &disabled, NULL, NULL);
   if (err && gpg_err_code(err) == GPG_ERR_EOF)
     {
       struct tm *tp;
@@ -810,10 +845,12 @@ add_control_entry (ctrl_t ctrl, const char *hexgrip, int ttl)
       /* Not yet in the file - add it. Because the file has been
          opened in append mode, we simply need to write to it.  */
       tp = localtime (&atime);
-      fprintf (fp, "# Key added on %04d-%02d-%02d %02d:%02d:%02d\n%s %d\n",
+      fprintf (fp, ("# Key added on: %04d-%02d-%02d %02d:%02d:%02d\n"
+                    "# Fingerprint:  %s\n"
+                    "%s %d%s\n"),
                1900+tp->tm_year, tp->tm_mon+1, tp->tm_mday,
                tp->tm_hour, tp->tm_min, tp->tm_sec,
-               hexgrip, ttl);
+               fmtfpr, hexgrip, ttl, confirm? " confirm":"");
 
     }
   fclose (fp);
@@ -834,7 +871,7 @@ ttl_from_sshcontrol (const char *hexgrip)
   if (open_control_file (&fp, 0))
     return 0; /* Error: Use the global default TTL.  */
 
-  if (search_control_file (fp, hexgrip, &disabled, &ttl)
+  if (search_control_file (fp, hexgrip, &disabled, &ttl, NULL)
       || disabled)
     ttl = 0;  /* Use the global default if not found or disabled.  */
 
@@ -844,6 +881,30 @@ ttl_from_sshcontrol (const char *hexgrip)
 }
 
 
+/* Scan the sshcontrol file and return the confirm flag.  */
+static int
+confirm_flag_from_sshcontrol (const char *hexgrip)
+{
+  FILE *fp;
+  int disabled, confirm;
+
+  if (!hexgrip || strlen (hexgrip) != 40)
+    return 1;  /* Wrong input: Better ask for confirmation.  */
+
+  if (open_control_file (&fp, 0))
+    return 1; /* Error: Better ask for confirmation.  */
+
+  if (search_control_file (fp, hexgrip, &disabled, NULL, &confirm)
+      || disabled)
+    confirm = 0;  /* If not found or disabled, there is no reason to
+                     ask for confirmation.  */
+
+  fclose (fp);
+
+  return confirm;
+}
+
+
 
 
 
@@ -1583,6 +1644,7 @@ ssh_key_grip (gcry_sexp_t key, unsigned char *buffer)
   return 0;
 }
 
+
 /* Converts the secret key KEY_SECRET into a public key, storing it in
    KEY_PUBLIC.  SPEC is the according key specification.  Returns zero
    on success or an error code.  */
@@ -1904,7 +1966,7 @@ ssh_handler_request_identities (ctrl_t ctrl,
           hexgrip[40] = 0;
           if ( strlen (hexgrip) != 40 )
             continue;
-          if (search_control_file (ctrl_fp, hexgrip, &disabled, NULL)
+          if (search_control_file (ctrl_fp, hexgrip, &disabled, NULL, NULL)
               || disabled)
             continue;
 
@@ -2039,14 +2101,60 @@ data_sign (ctrl_t ctrl, ssh_signature_encoder_t sig_encoder,
   const char *elems;
   size_t elems_n;
   gcry_mpi_t *mpis = NULL;
+  char hexgrip[40+1];
 
   *sig = NULL;
   *sig_n = 0;
 
+  /* Quick check to see whether we have a valid keygrip and convert it
+     to hex.  */
+  if (!ctrl->have_keygrip)
+    {
+      err = gpg_error (GPG_ERR_NO_SECKEY);
+      goto out;
+    }
+  bin2hex (ctrl->keygrip, 20, hexgrip);
+
+  /* Ask for confirmation if needed.  */
+  if (confirm_flag_from_sshcontrol (hexgrip))
+    {
+      gcry_sexp_t key;
+      char *fpr, *prompt;
+      char *comment = NULL;
+
+      err = agent_raw_key_from_file (ctrl, ctrl->keygrip, &key);
+      if (err)
+        goto out;
+      err = ssh_get_fingerprint_string (key, &fpr);
+      if (!err)
+        {
+          gcry_sexp_t tmpsxp = gcry_sexp_find_token (key, "comment", 0);
+          if (tmpsxp)
+            comment = gcry_sexp_nth_string (tmpsxp, 1);
+          gcry_sexp_release (tmpsxp);
+        }
+      gcry_sexp_release (key);
+      if (err)
+        goto out;
+      prompt = xtryasprintf (_("An ssh process requested the use of key%%0A"
+                               "  %s%%0A"
+                               "  (%s)%%0A"
+                               "Do you want to allow this?"),
+                             fpr, comment? comment:"");
+      xfree (fpr);
+      gcry_free (comment);
+      err = agent_get_confirmation (ctrl, prompt, _("Allow"), _("Deny"), 0);
+      xfree (prompt);
+      if (err)
+        goto out;
+    }
+
+  /* Create signature.  */
   ctrl->use_auth_call = 1;
   err = agent_pksign_do (ctrl,
                          _("Please enter the passphrase "
-                           "for the ssh key%0A  %c"), &signature_sexp,
+                           "for the ssh key%%0A  %F%%0A  (%c)"),
+                         &signature_sexp,
                          CACHE_MODE_SSH, ttl_from_sshcontrol);
   ctrl->use_auth_call = 0;
   if (err)
@@ -2365,7 +2473,7 @@ reenter_compare_cb (struct pin_entry_info_s *pi)
    our key storage, don't do anything.  When entering a new key also
    add an entry to the sshcontrol file.  */
 static gpg_error_t
-ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
+ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl, int confirm)
 {
   gpg_error_t err;
   unsigned char key_grip_raw[20];
@@ -2375,6 +2483,7 @@ ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
   char *description = NULL;
   const char *description2 = _("Please re-enter this passphrase");
   char *comment = NULL;
+  char *key_fpr = NULL;
   const char *initial_errtext = NULL;
   unsigned int i;
   struct pin_entry_info_s *pi = NULL, *pi2;
@@ -2388,6 +2497,9 @@ ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
   if ( !agent_key_available (key_grip_raw) )
     goto out; /* Yes, key is available.  */
 
+  err = ssh_get_fingerprint_string (key, &key_fpr);
+  if (err)
+    goto out;
 
   err = ssh_key_extract_comment (key, &comment);
   if (err)
@@ -2397,8 +2509,9 @@ ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
                  _("Please enter a passphrase to protect"
                    " the received secret key%%0A"
                    "   %s%%0A"
+                   "   %s%%0A"
                    "within gpg-agent's key storage"),
-                 comment ? comment : "?") < 0)
+                 key_fpr, comment ? comment : "") < 0)
     {
       err = gpg_error_from_syserror ();
       goto out;
@@ -2455,7 +2568,7 @@ ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
     goto out;
 
   /* And add an entry to the sshcontrol file.  */
-  err = add_control_entry (ctrl, key_grip, ttl);
+  err = add_control_entry (ctrl, key_grip, key_fpr, ttl, confirm);
 
 
  out:
@@ -2464,6 +2577,7 @@ ssh_identity_register (ctrl_t ctrl, gcry_sexp_t key, int ttl)
   xfree (pi);
   xfree (buffer);
   xfree (comment);
+  xfree (key_fpr);
   xfree (description);
 
   return err;
@@ -2548,9 +2662,7 @@ ssh_handler_add_identity (ctrl_t ctrl, estream_t request, estream_t response)
   if (err)
     goto out;
 
-  /* FIXME: are constraints used correctly?  */
+  err = ssh_identity_register (ctrl, key, ttl, confirm);
-
-  err = ssh_identity_register (ctrl, key, ttl);
 
  out:
 

agent/findkey.c

@@ -1,6 +1,6 @@
 /* findkey.c - Locate the secret key
- * Copyright (C) 2001, 2002, 2003, 2004, 2005,
+ * Copyright (C) 2001, 2002, 2003, 2004, 2005, 2007,
- *               2007  Free Software Foundation, Inc.
+ *               2010, 2011 Free Software Foundation, Inc.
  *
  * This file is part of GnuPG.
  *
@@ -33,6 +33,7 @@
 
 #include "agent.h"
 #include "i18n.h"
+#include "../common/ssh-utils.h"
 
 #ifndef O_BINARY
 #define O_BINARY 0
@@ -209,12 +210,14 @@ try_unprotect_cb (struct pin_entry_info_s *pi)
 
    %% - Replaced by a single %
    %c - Replaced by the content of COMMENT.
+   %F - Replaced by an ssh style fingerprint computed from KEY.
 
    The functions returns 0 on success or an error code.  On success a
    newly allocated string is stored at the address of RESULT.
  */
 static gpg_error_t
-modify_description (const char *in, const char *comment, char **result)
+modify_description (const char *in, const char *comment, const gcry_sexp_t key,
+                    char **result)
 {
   size_t comment_length;
   size_t in_len;
@@ -222,6 +225,7 @@ modify_description (const char *in, const char *comment, char **result)
   char *out;
   size_t i;
   int special, pass;
+  char *ssh_fpr = NULL;
 
   comment_length = strlen (comment);
   in_len  = strlen (in);
@@ -257,6 +261,18 @@ modify_description (const char *in, const char *comment, char **result)
                     out_len += comment_length;
                   break;
 
+                case 'F': /* SSH style fingerprint.  */
+                  if (!ssh_fpr && key)
+                    ssh_get_fingerprint_string (key, &ssh_fpr);
+                  if (ssh_fpr)
+                    {
+                      if (out)
+                        out = stpcpy (out, ssh_fpr);
+                      else
+                        out_len += strlen (ssh_fpr);
+                    }
+                  break;
+
                 default: /* Invalid special sequences are kept as they are. */
                   if (out)
                     {
@@ -283,12 +299,16 @@ modify_description (const char *in, const char *comment, char **result)
         {
           *result = out = xtrymalloc (out_len + 1);
           if (!out)
-            return gpg_error_from_syserror ();
+            {
+              xfree (ssh_fpr);
+              return gpg_error_from_syserror ();
+            }
         }
     }
 
   *out = 0;
   assert (*result + out_len == out);
+  xfree (ssh_fpr);
   return 0;
 }
 
@@ -529,45 +549,26 @@ agent_key_from_file (ctrl_t ctrl, const char *desc_text,
       break; /* no unprotection needed */
     case PRIVATE_KEY_PROTECTED:
       {
-	gcry_sexp_t comment_sexp;
-	size_t comment_length;
 	char *desc_text_final;
-	const char *comment = NULL;
+	char *comment = NULL;
 
         /* Note, that we will take the comment as a C string for
            display purposes; i.e. all stuff beyond a Nul character is
            ignored.  */
-	comment_sexp = gcry_sexp_find_token (s_skey, "comment", 0);
+        {
-	if (comment_sexp)
+          gcry_sexp_t comment_sexp;
-	  comment = gcry_sexp_nth_data (comment_sexp, 1, &comment_length);
+
-	if (!comment)
+          comment_sexp = gcry_sexp_find_token (s_skey, "comment", 0);
-	  {
+          if (comment_sexp)
-	    comment = "";
+            comment = gcry_sexp_nth_string (comment_sexp, 1);
-	    comment_length = 0;
+          gcry_sexp_release (comment_sexp);
-	  }
+        }
 
         desc_text_final = NULL;
 	if (desc_text)
-	  {
+          rc = modify_description (desc_text, comment? comment:"", s_skey,
-            if (comment[comment_length])
+                                   &desc_text_final);
-              {
+        gcry_free (comment);
-                /* Not a C-string; create one.  We might here allocate
-                   more than actually displayed but well, that
-                   shouldn't be a problem.  */
-                char *tmp = xtrymalloc (comment_length+1);
-                if (!tmp)
-                  rc = gpg_error_from_syserror ();
-                else
-                  {
-                    memcpy (tmp, comment, comment_length);
-                    tmp[comment_length] = 0;
-                    rc = modify_description (desc_text, tmp, &desc_text_final);
-                    xfree (tmp);
-                  }
-              }
-            else
-              rc = modify_description (desc_text, comment, &desc_text_final);
-	  }
 
 	if (!rc)
 	  {
@@ -578,7 +579,6 @@ agent_key_from_file (ctrl_t ctrl, const char *desc_text,
 			 gpg_strerror (rc));
 	  }
 
-	gcry_sexp_release (comment_sexp);
 	xfree (desc_text_final);
       }
       break;
@@ -638,6 +638,27 @@ agent_key_from_file (ctrl_t ctrl, const char *desc_text,
 }
 
 
+/* Return the key for the keygrip GRIP.  The result is stored at
+   RESULT.  This function extracts the key from the private key
+   database and returns it as an S-expression object as it is.  On
+   failure an error code is returned and NULL stored at RESULT. */
+gpg_error_t
+agent_raw_key_from_file (ctrl_t ctrl, const unsigned char *grip,
+                         gcry_sexp_t *result)
+{
+  gpg_error_t err;
+  gcry_sexp_t s_skey;
+
+  (void)ctrl;
+
+  *result = NULL;
+
+  err = read_key_file (grip, &s_skey);
+  if (!err)
+    *result = s_skey;
+  return err;
+}
+
 
 /* Return the public key for the keygrip GRIP.  The result is stored
    at RESULT.  This function extracts the public key from the private

common/Makefile.am

@@ -123,21 +123,8 @@ endif
 #
 # Module tests
 #
-<<<<<<< HEAD
 module_tests = t-convert t-percent t-gettime t-sysutils t-sexputil t-exechelp \
-	       t-session-env
+	       t-session-env t-ssh-utils
-=======
-t_jnlib_src = t-support.c t-support.h
-jnlib_tests = t-stringhelp t-timestuff
-if HAVE_W32_SYSTEM
-jnlib_tests += t-w32-reg
-endif
-module_tests = t-convert t-percent t-gettime t-sysutils t-sexputil \
-	       t-session-env t-openpgp-oid t-ssh-utils
-if !HAVE_W32CE_SYSTEM
-module_tests += t-exechelp
-endif
->>>>>>> New functions to compute an ssh style fingerprint.
 module_maint_tests = t-helpfile t-b64
 
 t_common_ldadd = libcommon.a ../jnlib/libjnlib.a ../gl/libgnu.a \
@@ -152,9 +139,4 @@ t_sexputil_LDADD = $(t_common_ldadd)
 t_b64_LDADD = $(t_common_ldadd)
 t_exechelp_LDADD = $(t_common_ldadd)
 t_session_env_LDADD = $(t_common_ldadd)
-<<<<<<< HEAD
-
-=======
-t_openpgp_oid_LDADD = $(t_common_ldadd)
 t_ssh_utils_LDADD = $(t_common_ldadd)
->>>>>>> New functions to compute an ssh style fingerprint.

common/t-ssh-utils.c

@@ -27,13 +27,6 @@
 #include "util.h"
 #include "ssh-utils.h"
 
-#define pass()  do { ; } while(0)
-#define fail(a,e)                                                       \
-  do { fprintf (stderr, "%s:%d: test %d failed (%s)\n",                 \
-                __FILE__,__LINE__, (a), gpg_strerror (e));              \
-    exit (1);                                                           \
-  } while(0)
-
 
 static struct { const char *key; const char *fpr; } sample_keys[] = {
   { "(protected-private-key "

doc/gpg-agent.texi

@@ -640,6 +640,12 @@ digits, optionally followed by the caching TTL in seconds and another
 optional field for arbitrary flags.  A non-zero TTL overrides the global
 default as set by @option{--default-cache-ttl-ssh}.
 
+The only flag support is @code{confirm}.  If this flag is found for a
+key, each use of the key will pop up a pinentry to confirm the use of
+that key.  The flag is automatically set if a new key was loaded into
+@code{gpg-agent} using the option @option{-c} of the @code{ssh-add}
+command.
+
 The keygrip may be prefixed with a @code{!} to disable an entry entry.
     
 The following example lists exactly one key.  Note that keys available
@@ -647,8 +653,9 @@ through a OpenPGP smartcard in the active smartcard reader are
 implicitly added to this list; i.e. there is no need to list them.
   
   @example
-  # Key added on 2005-02-25 15:08:29
+  # Key added on: 2011-07-20 20:38:46
-  5A6592BF45DC73BD876874A28FD4639282E29B52 0
+  # Fingerprint:  5e:8d:c4:ad:e7:af:6e:27:8a:d6:13:e4:79:ad:0b:81
+  34B62F25E277CF13D3C6BCEBFD3F85D08F0A864B 0 confirm
   @end example
 
 @item private-keys-v1.d/