Moved 1.9 branch to trunk

1 files changed, 2880 insertions, 0 deletions

diff --git a/agent/command-ssh.c b/agent/command-ssh.c
new file mode 100644
index 000000000..4e81aa2f2
--- /dev/null
+++ b/agent/command-ssh.c
@@ -0,0 +1,2880 @@
+/* command-ssh.c - gpg-agent's ssh-agent emulation layer
+ * Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
+ * USA.
+ */
+
+/* Only v2 of the ssh-agent protocol is implemented.  */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <assert.h>
+
+#include "agent.h"
+
+#include "estream.h"
+#include "i18n.h"
+
+
+
+/* Request types. */
+#define SSH_REQUEST_REQUEST_IDENTITIES    11
+#define SSH_REQUEST_SIGN_REQUEST          13
+#define SSH_REQUEST_ADD_IDENTITY          17
+#define SSH_REQUEST_REMOVE_IDENTITY       18
+#define SSH_REQUEST_REMOVE_ALL_IDENTITIES 19
+#define SSH_REQUEST_LOCK                  22
+#define SSH_REQUEST_UNLOCK                23
+#define SSH_REQUEST_ADD_ID_CONSTRAINED    25
+
+/* Options. */
+#define	SSH_OPT_CONSTRAIN_LIFETIME	   1
+#define	SSH_OPT_CONSTRAIN_CONFIRM	   2
+
+/* Response types. */
+#define SSH_RESPONSE_SUCCESS               6
+#define SSH_RESPONSE_FAILURE               5
+#define SSH_RESPONSE_IDENTITIES_ANSWER    12
+#define SSH_RESPONSE_SIGN_RESPONSE        14
+
+/* Other constants.  */
+#define SSH_DSA_SIGNATURE_PADDING 20
+#define SSH_DSA_SIGNATURE_ELEMS    2
+#define SPEC_FLAG_USE_PKCS1V2 (1 << 0)
+
+
+/* The blurb we put into the header of a newly created control file.  */
+static const char sshcontrolblurb[] =
+"# List of allowed ssh keys.  Only keys present in this file are used\n"
+"# in the SSH protocol.  The ssh-add tool may add new entries to this\n"
+"# file to enable them; you may also add them manually.  Comment\n"
+"# lines, like this one, as well as empty lines are ignored.  Lines do\n"
+"# have a certain length limit but this is not serious limitation as\n" 
+"# the format of the entries is fixed and checked by gpg-agent. A\n"
+"# non-comment line starts with optional white spaces, followed by the\n"
+"# keygrip of the key given as 40 hex digits, optionally followed by a\n"
+"# the caching TTL in seconds and another optional field for arbitrary\n"
+"# flags.   Prepend the keygrip with an '!' mark to disable it.\n"
+"\n";
+
+
+
+/* Macros.  */
+
+/* Return a new uint32 with b0 being the most significant byte and b3
+   being the least significant byte.  */
+#define uint32_construct(b0, b1, b2, b3) \
+  ((b0 << 24) | (b1 << 16) | (b2 << 8) | b3)
+
+
+
+
+/*
+ * Basic types.
+ */
+
+/* Type for a request handler.  */
+typedef gpg_error_t (*ssh_request_handler_t) (ctrl_t ctrl,
+					      estream_t request,
+					      estream_t response);
+
+/* Type, which is used for associating request handlers with the
+   appropriate request IDs.  */
+typedef struct ssh_request_spec
+{
+  unsigned char type;
+  ssh_request_handler_t handler;
+  const char *identifier;
+  unsigned int secret_input;
+} ssh_request_spec_t;
+
+/* Type for "key modifier functions", which are necessary since
+   OpenSSH and GnuPG treat key material slightly different.  A key
+   modifier is called right after a new key identity has been received
+   in order to "sanitize" the material.  */
+typedef gpg_error_t (*ssh_key_modifier_t) (const char *elems,
+                                           gcry_mpi_t *mpis);
+
+/* The encoding of a generated signature is dependent on the
+   algorithm; therefore algorithm specific signature encoding
+   functions are necessary.  */
+typedef gpg_error_t (*ssh_signature_encoder_t) (estream_t signature_blob,
+						gcry_mpi_t *mpis);
+
+/* Type, which is used for boundling all the algorithm specific
+   information together in a single object.  */
+typedef struct ssh_key_type_spec
+{
+  /* Algorithm identifier as used by OpenSSH.  */
+  const char *ssh_identifier;
+
+  /* Algorithm identifier as used by GnuPG.  */
+  const char *identifier;
+
+  /* List of MPI names for secret keys; order matches the one of the
+     agent protocol.  */
+  const char *elems_key_secret;
+
+  /* List of MPI names for public keys; order matches the one of the
+     agent protocol.  */
+  const char *elems_key_public;
+
+  /* List of MPI names for signature data.  */
+  const char *elems_signature;
+
+  /* List of MPI names for secret keys; order matches the one, which
+     is required by gpg-agent's key access layer.  */
+  const char *elems_sexp_order;
+
+  /* Key modifier function.  Key modifier functions are necessary in
+     order to fix any inconsistencies between the representation of
+     keys on the SSH and on the GnuPG side.  */
+  ssh_key_modifier_t key_modifier;
+
+  /* Signature encoder function.  Signature encoder functions are
+     necessary since the encoding of signatures depends on the used
+     algorithm.  */
+  ssh_signature_encoder_t signature_encoder;
+
+  /* Misc flags.  */
+  unsigned int flags;
+} ssh_key_type_spec_t;
+
+
+/* Prototypes.  */
+static gpg_error_t ssh_handler_request_identities (ctrl_t ctrl,
+						   estream_t request,
+						   estream_t response);
+static gpg_error_t ssh_handler_sign_request (ctrl_t ctrl,
+					     estream_t request,
+					     estream_t response);
+static gpg_error_t ssh_handler_add_identity (ctrl_t ctrl,
+					     estream_t request,
+					     estream_t response);
+static gpg_error_t ssh_handler_remove_identity (ctrl_t ctrl,
+						estream_t request,
+						estream_t response);
+static gpg_error_t ssh_handler_remove_all_identities (ctrl_t ctrl,
+						      estream_t request,
+						      estream_t response);
+static gpg_error_t ssh_handler_lock (ctrl_t ctrl,
+				     estream_t request,
+				     estream_t response);
+static gpg_error_t ssh_handler_unlock (ctrl_t ctrl,
+				       estream_t request,
+				       estream_t response);
+
+static gpg_error_t ssh_key_modifier_rsa (const char *elems, gcry_mpi_t *mpis);
+static gpg_error_t ssh_signature_encoder_rsa (estream_t signature_blob,
+                                              gcry_mpi_t *mpis);
+static gpg_error_t ssh_signature_encoder_dsa (estream_t signature_blob,
+                                              gcry_mpi_t *mpis);
+
+
+
+/* Global variables.  */
+   
+
+/* Associating request types with the corresponding request
+   handlers.  */
+
+static ssh_request_spec_t request_specs[] =
+  {
+#define REQUEST_SPEC_DEFINE(id, name, secret_input) \
+  { SSH_REQUEST_##id, ssh_handler_##name, #name, secret_input }
+
+    REQUEST_SPEC_DEFINE (REQUEST_IDENTITIES,    request_identities,    1),
+    REQUEST_SPEC_DEFINE (SIGN_REQUEST,          sign_request,          0),
+    REQUEST_SPEC_DEFINE (ADD_IDENTITY,          add_identity,          1),
+    REQUEST_SPEC_DEFINE (ADD_ID_CONSTRAINED,    add_identity,          1),
+    REQUEST_SPEC_DEFINE (REMOVE_IDENTITY,       remove_identity,       0),
+    REQUEST_SPEC_DEFINE (REMOVE_ALL_IDENTITIES, remove_all_identities, 0),
+    REQUEST_SPEC_DEFINE (LOCK,                  lock,                  0),
+    REQUEST_SPEC_DEFINE (UNLOCK,                unlock,                0)
+#undef REQUEST_SPEC_DEFINE
+  };
+
+
+/* Table holding key type specifications.  */
+static ssh_key_type_spec_t ssh_key_types[] =
+  {
+    {
+      "ssh-rsa", "rsa", "nedupq", "en",   "s",  "nedpqu",
+      ssh_key_modifier_rsa, ssh_signature_encoder_rsa,
+      SPEC_FLAG_USE_PKCS1V2
+    },
+    {
+      "ssh-dss", "dsa", "pqgyx",  "pqgy", "rs", "pqgyx",
+      NULL,                 ssh_signature_encoder_dsa,
+      0
+    },
+  };
+
+
+
+
+
+/*
+   General utility functions. 
+ */
+
+/* A secure realloc, i.e. it makes sure to allocate secure memory if A
+   is NULL.  This is required because the standard gcry_realloc does
+   not know whether to allocate secure or normal if NULL is passed as
+   existing buffer.  */
+static void *
+realloc_secure (void *a, size_t n)
+{
+  void *p;
+  
+  if (a)
+    p = gcry_realloc (a, n);
+  else
+    p = gcry_malloc_secure (n);
+
+  return p;
+}
+
+
+/* Create and return a new C-string from DATA/DATA_N (i.e.: add
+   NUL-termination); return NULL on OOM.  */
+static char *
+make_cstring (const char *data, size_t data_n)
+{
+  char *s;
+
+  s = xtrymalloc (data_n + 1);
+  if (s)
+    {
+      memcpy (s, data, data_n);
+      s[data_n] = 0;
+    }
+
+  return s;
+}
+
+
+
+
+/* 
+   Primitive I/O functions.  
+ */
+
+
+/* Read a byte from STREAM, store it in B.  */
+static gpg_error_t
+stream_read_byte (estream_t stream, unsigned char *b)
+{
+  gpg_error_t err;
+  int ret;
+
+  ret = es_fgetc (stream);
+  if (ret == EOF)
+    {
+      if (es_ferror (stream))
+	err = gpg_error_from_errno (errno);
+      else
+	err = gpg_error (GPG_ERR_EOF);
+      *b = 0;
+    }
+  else
+    {
+      *b = ret & 0xFF;
+      err = 0;
+    }
+
+  return err;
+}
+
+/* Write the byte contained in B to STREAM.  */
+static gpg_error_t
+stream_write_byte (estream_t stream, unsigned char b)
+{
+  gpg_error_t err;
+  int ret;
+
+  ret = es_fputc (b, stream);
+  if (ret == EOF)
+    err = gpg_error_from_errno (errno);
+  else
+    err = 0;
+
+  return err;
+}
+
+/* Read a uint32 from STREAM, store it in UINT32.  */
+static gpg_error_t
+stream_read_uint32 (estream_t stream, u32 *uint32)
+{
+  unsigned char buffer[4];
+  size_t bytes_read;
+  gpg_error_t err;
+  int ret;
+
+  ret = es_read (stream, buffer, sizeof (buffer), &bytes_read);
+  if (ret)
+    err = gpg_error_from_errno (errno);
+  else
+    {
+      if (bytes_read != sizeof (buffer))
+	err = gpg_error (GPG_ERR_EOF);
+      else
+	{
+	  u32 n;
+
+	  n = uint32_construct (buffer[0], buffer[1], buffer[2], buffer[3]);
+	  *uint32 = n;
+	  err = 0;
+	}
+    }
+
+  return err;
+}
+
+/* Write the uint32 contained in UINT32 to STREAM.  */
+static gpg_error_t
+stream_write_uint32 (estream_t stream, u32 uint32)
+{
+  unsigned char buffer[4];
+  gpg_error_t err;
+  int ret;
+
+  buffer[0] = uint32 >> 24;
+  buffer[1] = uint32 >> 16;
+  buffer[2] = uint32 >>  8;
+  buffer[3] = uint32 >>  0;
+
+  ret = es_write (stream, buffer, sizeof (buffer), NULL);
+  if (ret)
+    err = gpg_error_from_errno (errno);
+  else
+    err = 0;
+
+  return err;
+}
+
+/* Read SIZE bytes from STREAM into BUFFER.  */
+static gpg_error_t
+stream_read_data (estream_t stream, unsigned char *buffer, size_t size)
+{
+  gpg_error_t err;
+  size_t bytes_read;
+  int ret;
+
+  ret = es_read (stream, buffer, size, &bytes_read);
+  if (ret)
+    err = gpg_error_from_errno (errno);
+  else
+    {
+      if (bytes_read != size)
+	err = gpg_error (GPG_ERR_EOF);
+      else
+	err = 0;
+    }
+
+  return err;
+}
+
+/* Write SIZE bytes from BUFFER to STREAM.  */
+static gpg_error_t
+stream_write_data (estream_t stream, const unsigned char *buffer, size_t size)
+{
+  gpg_error_t err;
+  int ret;
+
+  ret = es_write (stream, buffer, size, NULL);
+  if (ret)
+    err = gpg_error_from_errno (errno);
+  else
+    err = 0;
+
+  return err;
+}
+
+/* Read a binary string from STREAM into STRING, store size of string
+   in STRING_SIZE; depending on SECURE use secure memory for
+   string.  */
+static gpg_error_t
+stream_read_string (estream_t stream, unsigned int secure,
+		    unsigned char **string, u32 *string_size)
+{
+  gpg_error_t err;
+  unsigned char *buffer;
+  u32 length;
+
+  buffer = NULL;
+
+  /* Read string length.  */
+  err = stream_read_uint32 (stream, &length);
+  if (err)
+    goto out;
+
+  /* Allocate space.  */
+  if (secure)
+    buffer = xtrymalloc_secure (length + 1);
+  else
+    buffer = xtrymalloc (length + 1);
+  if (! buffer)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  /* Read data.  */
+  err = stream_read_data (stream, buffer, length);
+  if (err)
+    goto out;
+
+  /* Finalize string object.  */
+  buffer[length] = 0;
+  *string = buffer;
+  if (string_size)
+    *string_size = length;
+
+ out:
+
+  if (err)
+    xfree (buffer);
+
+  return err;
+}
+
+/* Read a C-string from STREAM, store copy in STRING.  */
+static gpg_error_t
+stream_read_cstring (estream_t stream, char **string)
+{
+  unsigned char *buffer;
+  gpg_error_t err;
+
+  err = stream_read_string (stream, 0, &buffer, NULL);
+  if (err)
+    goto out;
+  
+  *string = (char *) buffer;
+
+ out:
+
+  return err;
+}
+
+
+/* Write a binary string from STRING of size STRING_N to STREAM.  */
+static gpg_error_t
+stream_write_string (estream_t stream,
+		     const unsigned char *string, u32 string_n)
+{
+  gpg_error_t err;
+
+  err = stream_write_uint32 (stream, string_n);
+  if (err)
+    goto out;
+
+  err = stream_write_data (stream, string, string_n);
+
+ out:
+
+  return err;
+}
+
+/* Write a C-string from STRING to STREAM.  */
+static gpg_error_t
+stream_write_cstring (estream_t stream, const char *string)
+{
+  gpg_error_t err;
+
+  err = stream_write_string (stream,
+			     (const unsigned char *) string, strlen (string));
+
+  return err;
+}			  
+
+/* Read an MPI from STREAM, store it in MPINT.  Depending on SECURE
+   use secure memory.  */
+static gpg_error_t
+stream_read_mpi (estream_t stream, unsigned int secure, gcry_mpi_t *mpint)
+{
+  unsigned char *mpi_data;
+  u32 mpi_data_size;
+  gpg_error_t err;
+  gcry_mpi_t mpi;
+
+  mpi_data = NULL;
+
+  err = stream_read_string (stream, secure, &mpi_data, &mpi_data_size);
+  if (err)
+    goto out;
+
+  err = gcry_mpi_scan (&mpi, GCRYMPI_FMT_STD, mpi_data, mpi_data_size, NULL);
+  if (err)
+    goto out;
+
+  *mpint = mpi;
+
+ out:
+
+  xfree (mpi_data);
+
+  return err;
+}
+
+/* Write the MPI contained in MPINT to STREAM.  */
+static gpg_error_t
+stream_write_mpi (estream_t stream, gcry_mpi_t mpint)
+{
+  unsigned char *mpi_buffer;
+  size_t mpi_buffer_n;
+  gpg_error_t err;
+
+  mpi_buffer = NULL;
+
+  err = gcry_mpi_aprint (GCRYMPI_FMT_STD, &mpi_buffer, &mpi_buffer_n, mpint);
+  if (err)
+    goto out;
+
+  err = stream_write_string (stream, mpi_buffer, mpi_buffer_n);
+
+ out:
+
+  xfree (mpi_buffer);
+
+  return err;
+}
+
+/* Copy data from SRC to DST until EOF is reached.  */
+static gpg_error_t
+stream_copy (estream_t dst, estream_t src)
+{
+  char buffer[BUFSIZ];
+  size_t bytes_read;
+  gpg_error_t err;
+  int ret;
+
+  err = 0;
+  while (1)
+    {
+      ret = es_read (src, buffer, sizeof (buffer), &bytes_read);
+      if (ret || (! bytes_read))
+	{
+	  if (ret)
+	    err = gpg_error_from_errno (errno);
+	  break;
+	}
+      ret = es_write (dst, buffer, bytes_read, NULL);
+      if (ret)
+	{
+	  err = gpg_error_from_errno (errno);
+	  break;
+	}
+    }
+
+  return err;
+}
+
+
+/* Read the content of the file specified by FILENAME into a newly
+   create buffer, which is to be stored in BUFFER; store length of
+   buffer in BUFFER_N.  */
+static gpg_error_t
+file_to_buffer (const char *filename, unsigned char **buffer, size_t *buffer_n)
+{
+  unsigned char *buffer_new;
+  struct stat statbuf;
+  estream_t stream;
+  gpg_error_t err;
+  int ret;
+
+  *buffer = NULL;
+  *buffer_n = 0;
+
+  buffer_new = NULL;
+  err = 0;
+  
+  stream = es_fopen (filename, "r");
+  if (! stream)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  ret = fstat (es_fileno (stream), &statbuf);
+  if (ret)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  buffer_new = xtrymalloc (statbuf.st_size);
+  if (! buffer_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  err = stream_read_data (stream, buffer_new, statbuf.st_size);
+  if (err)
+    goto out;
+
+  *buffer = buffer_new;
+  *buffer_n = statbuf.st_size;
+
+ out:
+
+  if (stream)
+    es_fclose (stream);
+
+  if (err)
+    xfree (buffer_new);
+
+  return err;
+}
+
+
+
+
+/* Open the ssh control file and create it if not available. With
+   APPEND passed as true the file will be opened in append mode,
+   otherwise in read only mode.  On success a file pointer is stored
+   at the address of R_FP. */
+static gpg_error_t
+open_control_file (FILE **r_fp, int append)
+{
+  gpg_error_t err;
+  char *fname;
+  FILE *fp;
+
+  /* Note: As soon as we start to use non blocking functions here
+     (i.e. where Pth might switch threads) we need to employ a
+     mutex.  */
+  *r_fp = NULL;
+  fname = make_filename (opt.homedir, "sshcontrol", NULL);
+  /* FIXME: With "a+" we are not able to check whether this will will
+     be created and thus the blurb needs to be written first.  */
+  fp = fopen (fname, append? "a+":"r");
+  if (!fp && errno == ENOENT)
+    {
+      /* Fixme: "x" is a GNU extension.  We might want to use the es_
+         functions here.  */
+      fp = fopen (fname, "wx");  
+      if (!fp)
+        {
+          err = gpg_error (gpg_err_code_from_errno (errno));
+          log_error (_("can't create `%s': %s\n"), fname, gpg_strerror (err));
+          xfree (fname);
+          return err;
+        }
+      fputs (sshcontrolblurb, fp);
+      fclose (fp);
+      fp = fopen (fname, append? "a+":"r");
+    }
+
+  if (!fp)
+    {
+      err = gpg_error (gpg_err_code_from_errno (errno));
+      log_error (_("can't open `%s': %s\n"), fname, gpg_strerror (err));
+      xfree (fname);
+      return err;
+    }
+  
+  *r_fp = fp;  
+
+  return 0;
+}
+
+
+/* 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.  */
+static gpg_error_t
+search_control_file (FILE *fp, const char *hexgrip, int *disabled)
+{
+  int c, i;
+  char *p, line[256];
+  
+  assert (strlen (hexgrip) == 40 );
+
+  rewind (fp);
+  *disabled = 0;
+ next_line:
+  do
+    {
+      if (!fgets (line, DIM(line)-1, fp) )
+        {
+          if (feof (fp))
+            return gpg_error (GPG_ERR_EOF);
+          return gpg_error (gpg_err_code_from_errno (errno));
+        }
+      
+      if (!*line || line[strlen(line)-1] != '\n')
+        {
+          /* Eat until end of line */
+          while ( (c=getc (fp)) != EOF && c != '\n')
+            ;
+          return gpg_error (*line? GPG_ERR_LINE_TOO_LONG
+                                 : GPG_ERR_INCOMPLETE_LINE);
+        }
+      
+      /* Allow for empty lines and spaces */
+      for (p=line; spacep (p); p++)
+        ;
+    }
+  while (!*p || *p == '\n' || *p == '#');
+  
+  *disabled = 0;
+  if (*p == '!')
+    {
+      *disabled = 1;
+      for (p++; spacep (p); p++)
+        ;
+    }
+
+  for (i=0; hexdigitp (p) && i < 40; p++, i++)
+    if (hexgrip[i] != (*p >= 'a'? (*p & 0xdf): *p))
+      goto next_line;
+  if (i != 40 || !(spacep (p) || *p == '\n'))
+    {
+      log_error ("invalid formatted line in ssh control file\n");
+      return gpg_error (GPG_ERR_BAD_DATA);
+    }
+
+  /* Fixme: Get TTL and flags.  */
+
+  return 0; /* Okay:  found it.  */
+}
+
+
+
+/* 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
+   through the ssh-add function.  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)
+{
+  gpg_error_t err;
+  FILE *fp;
+  int disabled;
+
+  err = open_control_file (&fp, 1);
+  if (err)
+    return err;
+
+  err = search_control_file (fp, hexgrip, &disabled);
+  if (err && gpg_err_code(err) == GPG_ERR_EOF)
+    {
+      struct tm *tp;
+      time_t atime = time (NULL);
+
+      /* Not yet in the file - add it. Becuase 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",
+               1900+tp->tm_year, tp->tm_mon+1, tp->tm_mday,
+               tp->tm_hour, tp->tm_min, tp->tm_sec,
+               hexgrip, ttl);
+               
+    }
+  fclose (fp);
+  return 0;
+}
+
+
+
+
+
+/*
+
+  MPI lists. 
+
+ */
+
+/* Free the list of MPIs MPI_LIST.  */
+static void
+mpint_list_free (gcry_mpi_t *mpi_list)
+{
+  if (mpi_list)
+    {
+      unsigned int i;
+
+      for (i = 0; mpi_list[i]; i++)
+	gcry_mpi_release (mpi_list[i]);
+      xfree (mpi_list);
+    }
+}
+
+/* Receive key material MPIs from STREAM according to KEY_SPEC;
+   depending on SECRET expect a public key or secret key.  The newly
+   allocated list of MPIs is stored in MPI_LIST.  Returns usual error
+   code.  */
+static gpg_error_t
+ssh_receive_mpint_list (estream_t stream, int secret,
+			ssh_key_type_spec_t key_spec, gcry_mpi_t **mpi_list)
+{
+  unsigned int elems_public_n;
+  const char *elems_public;
+  unsigned int elems_n;
+  const char *elems;
+  int elem_is_secret;
+  gcry_mpi_t *mpis;
+  gpg_error_t err;
+  unsigned int i;
+
+  mpis = NULL;
+  err = 0;
+  
+  if (secret)
+    elems = key_spec.elems_key_secret;
+  else
+    elems = key_spec.elems_key_public;
+  elems_n = strlen (elems);
+
+  elems_public = key_spec.elems_key_public;
+  elems_public_n = strlen (elems_public);
+
+  mpis = xtrycalloc (elems_n + 1, sizeof *mpis );
+  if (!mpis)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  elem_is_secret = 0;
+  for (i = 0; i < elems_n; i++)
+    {
+      if (secret)
+	elem_is_secret = ! strchr (elems_public, elems[i]);
+      err = stream_read_mpi (stream, elem_is_secret, &mpis[i]);
+      if (err)
+	break;
+    }
+  if (err)
+    goto out;
+
+  *mpi_list = mpis;
+
+ out:
+
+  if (err)
+    mpint_list_free (mpis);
+
+  return err;
+}
+
+
+
+/* Key modifier function for RSA.  */
+static gpg_error_t
+ssh_key_modifier_rsa (const char *elems, gcry_mpi_t *mpis)
+{
+  gcry_mpi_t p;
+  gcry_mpi_t q;
+  gcry_mpi_t u;
+
+  if (strcmp (elems, "nedupq"))
+    /* Modifying only necessary for secret keys.  */
+    goto out;
+
+  u = mpis[3];
+  p = mpis[4];
+  q = mpis[5];
+
+  if (gcry_mpi_cmp (p, q) > 0)
+    {
+      /* P shall be smaller then Q!  Swap primes.  iqmp becomes u.  */
+      gcry_mpi_t tmp;
+
+      tmp = mpis[4];
+      mpis[4] = mpis[5];
+      mpis[5] = tmp;
+    }
+  else
+    /* U needs to be recomputed.  */
+    gcry_mpi_invm (u, p, q);
+
+ out:
+
+  return 0;
+}
+
+/* Signature encoder function for RSA.  */
+static gpg_error_t
+ssh_signature_encoder_rsa (estream_t signature_blob, gcry_mpi_t *mpis)
+{
+  unsigned char *data;
+  size_t data_n;
+  gpg_error_t err;
+  gcry_mpi_t s;
+
+  s = mpis[0];
+
+  err = gcry_mpi_aprint (GCRYMPI_FMT_USG, &data, &data_n, s);
+  if (err)
+    goto out;
+
+  err = stream_write_string (signature_blob, data, data_n);
+  xfree (data);
+
+ out:
+
+  return err;
+}
+
+
+/* Signature encoder function for DSA.  */
+static gpg_error_t
+ssh_signature_encoder_dsa (estream_t signature_blob, gcry_mpi_t *mpis)
+{
+  unsigned char buffer[SSH_DSA_SIGNATURE_PADDING * SSH_DSA_SIGNATURE_ELEMS];
+  unsigned char *data;
+  size_t data_n;
+  gpg_error_t err;
+  int i;
+
+  data = NULL;
+
+  for (i = 0; i < 2; i++)
+    {
+      err = gcry_mpi_aprint (GCRYMPI_FMT_USG, &data, &data_n, mpis[i]);
+      if (err)
+	break;
+
+      if (data_n > SSH_DSA_SIGNATURE_PADDING)
+	{
+	  err = gpg_error (GPG_ERR_INTERNAL); /* FIXME?  */
+	  break;
+	}
+      
+      memset (buffer + (i * SSH_DSA_SIGNATURE_PADDING), 0,
+	      SSH_DSA_SIGNATURE_PADDING - data_n);
+      memcpy (buffer + (i * SSH_DSA_SIGNATURE_PADDING)
+	      + (SSH_DSA_SIGNATURE_PADDING - data_n), data, data_n);
+
+      xfree (data);
+      data = NULL;
+    }
+  if (err)
+    goto out;
+
+  err = stream_write_string (signature_blob, buffer, sizeof (buffer));
+
+ out:
+
+  xfree (data);
+
+  return err;
+}
+
+/* 
+   S-Expressions. 
+ */
+
+
+/* This function constructs a new S-Expression for the key identified
+   by the KEY_SPEC, SECRET, MPIS and COMMENT, which is to be stored in
+   *SEXP.  Returns usual error code.  */
+static gpg_error_t
+sexp_key_construct (gcry_sexp_t *sexp,
+		    ssh_key_type_spec_t key_spec, int secret,
+		    gcry_mpi_t *mpis, const char *comment)
+{
+  const char *key_identifier[] = { "public-key", "private-key" };
+  gcry_sexp_t sexp_new;
+  char *sexp_template;
+  size_t sexp_template_n;
+  gpg_error_t err;
+  const char *elems;
+  size_t elems_n;
+  unsigned int i;
+  unsigned int j;
+  void **arg_list;
+
+  err = 0;
+  sexp_new = NULL;
+  arg_list = NULL;
+  if (secret)
+    elems = key_spec.elems_sexp_order;
+  else
+    elems = key_spec.elems_key_public;
+  elems_n = strlen (elems);
+
+  /*
+    Calculate size for sexp_template_n:
+
+    "(%s(%s<mpis>)(comment%s))" -> 20 + sizeof (<mpis>).
+
+    mpi: (X%m) -> 5.
+
+  */
+  sexp_template_n = 20 + (elems_n * 5);
+  sexp_template = xtrymalloc (sexp_template_n);
+  if (! sexp_template)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  /* Key identifier, algorithm identifier, mpis, comment.  */
+  arg_list = xtrymalloc (sizeof (*arg_list) * (2 + elems_n + 1));
+  if (! arg_list)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  i = 0;
+  arg_list[i++] = &key_identifier[secret];
+  arg_list[i++] = &key_spec.identifier;
+
+  *sexp_template = 0;
+  sexp_template_n = 0;
+  sexp_template_n = sprintf (sexp_template + sexp_template_n, "(%%s(%%s");
+  for (i = 0; i < elems_n; i++)
+    {
+      sexp_template_n += sprintf (sexp_template + sexp_template_n, "(%c%%m)",
+				  elems[i]);
+      if (secret)
+	{
+	  for (j = 0; j < elems_n; j++)
+	    if (key_spec.elems_key_secret[j] == elems[i])
+	      break;
+	}
+      else
+	j = i;
+      arg_list[i + 2] = &mpis[j];
+    }
+  sexp_template_n += sprintf (sexp_template + sexp_template_n,
+			      ")(comment%%s))");
+
+  arg_list[i + 2] = &comment;
+
+  err = gcry_sexp_build_array (&sexp_new, NULL, sexp_template, arg_list);
+  if (err)
+    goto out;
+
+  *sexp = sexp_new;
+
+ out:
+
+  xfree (arg_list);
+  xfree (sexp_template);
+
+  return err;
+}
+
+/* This functions breaks up the key contained in the S-Expression SEXP
+   according to KEY_SPEC.  The MPIs are bundled in a newly create
+   list, which is to be stored in MPIS; a newly allocated string
+   holding the comment will be stored in COMMENT; SECRET will be
+   filled with a boolean flag specifying what kind of key it is.
+   Returns usual error code.  */
+static gpg_error_t
+sexp_key_extract (gcry_sexp_t sexp,
+		  ssh_key_type_spec_t key_spec, int *secret,
+		  gcry_mpi_t **mpis, char **comment)
+{
+  gpg_error_t err;
+  gcry_sexp_t value_list;
+  gcry_sexp_t value_pair;
+  gcry_sexp_t comment_list;
+  unsigned int i;
+  char *comment_new;
+  const char *data;
+  size_t data_n;
+  int is_secret;
+  size_t elems_n;
+  const char *elems;
+  gcry_mpi_t *mpis_new;
+  gcry_mpi_t mpi;
+
+  err = 0;
+  value_list = NULL;
+  value_pair = NULL;
+  comment_list = NULL;
+  comment_new = NULL;
+  mpis_new = NULL;
+
+  data = gcry_sexp_nth_data (sexp, 0, &data_n);
+  if (! data)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  if ((data_n == 10 && !strncmp (data, "public-key", 10))
+      || (data_n == 21 && !strncmp (data, "protected-private-key", 21))
+      || (data_n == 20 && !strncmp (data, "shadowed-private-key", 20)))
+    {
+      is_secret = 0;
+      elems = key_spec.elems_key_public;
+    }
+  else if (data_n == 11 && !strncmp (data, "private-key", 11))
+    {
+      is_secret = 1;
+      elems = key_spec.elems_key_secret;
+    }
+  else
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  elems_n = strlen (elems);
+  mpis_new = xtrycalloc (elems_n + 1, sizeof *mpis_new );
+  if (!mpis_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  value_list = gcry_sexp_find_token (sexp, key_spec.identifier, 0);
+  if (! value_list)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  for (i = 0; i < elems_n; i++)
+    {
+      value_pair = gcry_sexp_find_token (value_list, elems + i, 1);
+      if (! value_pair)
+	{
+	  err = gpg_error (GPG_ERR_INV_SEXP);
+	  break;
+	}
+
+      /* Note that we need to use STD format; i.e. prepend a 0x00 to
+         indicate a positive number if the high bit is set. */
+      mpi = gcry_sexp_nth_mpi (value_pair, 1, GCRYMPI_FMT_STD);
+      if (! mpi)
+	{
+	  err = gpg_error (GPG_ERR_INV_SEXP);
+	  break;
+	}
+      mpis_new[i] = mpi;
+      gcry_sexp_release (value_pair);
+      value_pair = NULL;
+    }
+  if (err)
+    goto out;
+
+  /* We do not require a comment sublist to be present here.  */
+  data = NULL;
+  data_n = 0;
+
+  comment_list = gcry_sexp_find_token (sexp, "comment", 0);
+  if (comment_list)
+    data = gcry_sexp_nth_data (comment_list, 1, &data_n);
+  if (! data)
+    {
+      data = "(none)";
+      data_n = 6;
+    }
+
+  comment_new = make_cstring (data, data_n);
+  if (! comment_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  if (secret)
+    *secret = is_secret;
+  *mpis = mpis_new;
+  *comment = comment_new;
+
+ out:
+
+  gcry_sexp_release (value_list);
+  gcry_sexp_release (value_pair);
+  gcry_sexp_release (comment_list);
+  
+  if (err)
+    {
+      xfree (comment_new);
+      mpint_list_free (mpis_new);
+    }
+
+  return err;
+}
+
+/* Extract the car from SEXP, and create a newly created C-string 
+   which is to be stored in IDENTIFIER.  */
+static gpg_error_t
+sexp_extract_identifier (gcry_sexp_t sexp, char **identifier)
+{
+  char *identifier_new;
+  gcry_sexp_t sublist;
+  const char *data;
+  size_t data_n;
+  gpg_error_t err;
+
+  identifier_new = NULL;
+  err = 0;
+  
+  sublist = gcry_sexp_nth (sexp, 1);
+  if (! sublist)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  data = gcry_sexp_nth_data (sublist, 0, &data_n);
+  if (! data)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  identifier_new = make_cstring (data, data_n);
+  if (! identifier_new)
+    {
+      err = gpg_err_code_from_errno (errno);
+      goto out;
+    }
+
+  *identifier = identifier_new;
+
+ out:
+
+  gcry_sexp_release (sublist);
+
+  return err;
+}
+
+
+
+/*
+
+  Key I/O.
+
+*/
+
+/* Search for a key specification entry.  If SSH_NAME is not NULL,
+   search for an entry whose "ssh_name" is equal to SSH_NAME;
+   otherwise, search for an entry whose "name" is equal to NAME.
+   Store found entry in SPEC on success, return error otherwise.  */
+static gpg_error_t
+ssh_key_type_lookup (const char *ssh_name, const char *name,
+		     ssh_key_type_spec_t *spec)
+{
+  gpg_error_t err;
+  unsigned int i;
+
+  for (i = 0; i < DIM (ssh_key_types); i++)
+    if ((ssh_name && (! strcmp (ssh_name, ssh_key_types[i].ssh_identifier)))
+	|| (name && (! strcmp (name, ssh_key_types[i].identifier))))
+      break;
+  
+  if (i == DIM (ssh_key_types))
+    err = gpg_error (GPG_ERR_NOT_FOUND);
+  else
+    {
+      *spec = ssh_key_types[i];
+      err = 0;
+    }
+
+  return err;
+}
+
+/* Receive a key from STREAM, according to the key specification given
+   as KEY_SPEC.  Depending on SECRET, receive a secret or a public
+   key.  If READ_COMMENT is true, receive a comment string as well.
+   Constructs a new S-Expression from received data and stores it in
+   KEY_NEW.  Returns zero on success or an error code.  */
+static gpg_error_t
+ssh_receive_key (estream_t stream, gcry_sexp_t *key_new, int secret,
+                 int read_comment, ssh_key_type_spec_t *key_spec)
+{
+  gpg_error_t err;
+  char *key_type;
+  char *comment;
+  gcry_sexp_t key;
+  ssh_key_type_spec_t spec;
+  gcry_mpi_t *mpi_list;
+  const char *elems;
+
+  mpi_list = NULL;
+  key_type = NULL;
+  comment = "";
+  key = NULL;
+  	
+  err = stream_read_cstring (stream, &key_type);
+  if (err)
+    goto out;
+
+  err = ssh_key_type_lookup (key_type, NULL, &spec);
+  if (err)
+    goto out;
+
+  err = ssh_receive_mpint_list (stream, secret, spec, &mpi_list);
+  if (err)
+    goto out;
+
+  if (read_comment)
+    {
+      err = stream_read_cstring (stream, &comment);
+      if (err)
+	goto out;
+    }
+
+  if (secret)
+    elems = spec.elems_key_secret;
+  else
+    elems = spec.elems_key_public;
+
+  if (spec.key_modifier)
+    {
+      err = (*spec.key_modifier) (elems, mpi_list);
+      if (err)
+	goto out;
+    }
+
+  err = sexp_key_construct (&key, spec, secret, mpi_list, comment);
+  if (err)
+    goto out;
+
+  if (key_spec)
+    *key_spec = spec;
+  *key_new = key;
+  
+ out:
+
+  mpint_list_free (mpi_list);
+  xfree (key_type);
+  if (read_comment)
+    xfree (comment);
+
+  return err;
+}
+
+/* Converts a key of type TYPE, whose key material is given in MPIS,
+   into a newly created binary blob, which is to be stored in
+   BLOB/BLOB_SIZE.  Returns zero on success or an error code.  */
+static gpg_error_t
+ssh_convert_key_to_blob (unsigned char **blob, size_t *blob_size,
+			 const char *type, gcry_mpi_t *mpis)
+{
+  unsigned char *blob_new;
+  long int blob_size_new;
+  estream_t stream;
+  gpg_error_t err;
+  unsigned int i;
+
+  *blob = NULL;
+  *blob_size = 0;
+
+  blob_new = NULL;
+  stream = NULL;
+  err = 0;
+
+  stream = es_mopen (NULL, 0, 0, 1, NULL, NULL, "r+");
+  if (! stream)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  err = stream_write_cstring (stream, type);
+  if (err)
+    goto out;
+
+  for (i = 0; mpis[i] && (! err); i++)
+    err = stream_write_mpi (stream, mpis[i]);
+  if (err)
+    goto out;
+
+  blob_size_new = es_ftell (stream);
+  if (blob_size_new == -1)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+  
+  err = es_fseek (stream, 0, SEEK_SET);
+  if (err)
+    goto out;
+
+  blob_new = xtrymalloc (blob_size_new);
+  if (! blob_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  err = stream_read_data (stream, blob_new, blob_size_new);
+  if (err)
+    goto out;
+
+  *blob = blob_new;
+  *blob_size = blob_size_new;
+
+ out:
+
+  if (stream)
+    es_fclose (stream);
+  if (err)
+    xfree (blob_new);
+
+  return err;
+}
+			      
+
+/* Write the public key KEY_PUBLIC to STREAM in SSH key format.  If
+   OVERRIDE_COMMENT is not NULL, it will be used instead of the
+   comment stored in the key.  */
+static gpg_error_t
+ssh_send_key_public (estream_t stream, gcry_sexp_t key_public,
+                     const char *override_comment)
+{
+  ssh_key_type_spec_t spec;
+  gcry_mpi_t *mpi_list;
+  char *key_type;
+  char *comment;
+  unsigned char *blob;
+  size_t blob_n;
+  gpg_error_t err;
+
+  key_type = NULL;
+  mpi_list = NULL;
+  comment = NULL;
+  blob = NULL;
+
+  err = sexp_extract_identifier (key_public, &key_type);
+  if (err)
+    goto out;
+
+  err = ssh_key_type_lookup (NULL, key_type, &spec);
+  if (err)
+    goto out;
+
+  err = sexp_key_extract (key_public, spec, NULL, &mpi_list, &comment);
+  if (err)
+    goto out;
+
+  err = ssh_convert_key_to_blob (&blob, &blob_n,
+                                 spec.ssh_identifier, mpi_list);
+  if (err)
+    goto out;
+  
+  err = stream_write_string (stream, blob, blob_n);
+  if (err)
+    goto out;
+
+  err = stream_write_cstring (stream,
+                              override_comment? override_comment : comment);
+  
+ out:
+
+  mpint_list_free (mpi_list);
+  xfree (key_type);
+  xfree (comment);
+  xfree (blob);
+
+  return err;
+}
+
+/* Read a public key out of BLOB/BLOB_SIZE according to the key
+   specification given as KEY_SPEC, storing the new key in KEY_PUBLIC.
+   Returns zero on success or an error code.  */
+static gpg_error_t
+ssh_read_key_public_from_blob (unsigned char *blob, size_t blob_size,
+			       gcry_sexp_t *key_public,
+			       ssh_key_type_spec_t *key_spec)
+{
+  estream_t blob_stream;
+  gpg_error_t err;
+
+  err = 0;
+  
+  blob_stream = es_mopen (NULL, 0, 0, 1, NULL, NULL, "r+");
+  if (! blob_stream)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  err = stream_write_data (blob_stream, blob, blob_size);
+  if (err)
+    goto out;
+
+  err = es_fseek (blob_stream, 0, SEEK_SET);
+  if (err)
+    goto out;
+
+  err = ssh_receive_key (blob_stream, key_public, 0, 0, key_spec);
+
+ out:
+
+  if (blob_stream)
+    es_fclose (blob_stream);
+
+  return err;
+}
+
+
+
+/* This function calculates the key grip for the key contained in the
+   S-Expression KEY and writes it to BUFFER, which must be large
+   enough to hold it.  Returns usual error code.  */
+static gpg_error_t
+ssh_key_grip (gcry_sexp_t key, unsigned char *buffer)
+{
+  if (!gcry_pk_get_keygrip (key, buffer))
+    return gpg_error (GPG_ERR_INTERNAL);
+
+  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.  */
+static gpg_error_t
+key_secret_to_public (gcry_sexp_t *key_public,
+		      ssh_key_type_spec_t spec, gcry_sexp_t key_secret)
+{
+  char *comment;
+  gcry_mpi_t *mpis;
+  gpg_error_t err;
+  int is_secret;
+
+  comment = NULL;
+  mpis = NULL;
+
+  err = sexp_key_extract (key_secret, spec, &is_secret, &mpis, &comment);
+  if (err)
+    goto out;
+
+  err = sexp_key_construct (key_public, spec, 0, mpis, comment);
+
+ out:
+
+  mpint_list_free (mpis);
+  xfree (comment);
+
+  return err;
+}
+
+
+/* Check whether a smartcard is available and whether it has a usable
+   key.  Store a copy of that key at R_PK and return 0.  If no key is
+   available store NULL at R_PK and return an error code.  If CARDSN
+   is not NULL, a string with the serial number of the card will be
+   a malloced and stored there. */
+static gpg_error_t
+card_key_available (ctrl_t ctrl, gcry_sexp_t *r_pk, char **cardsn)
+{
+  gpg_error_t err;
+  char *authkeyid;
+  char *serialno = NULL;
+  unsigned char *pkbuf;
+  size_t pkbuflen;
+  gcry_sexp_t s_pk;
+  unsigned char grip[20];
+
+  *r_pk = NULL;
+  if (cardsn)
+    *cardsn = NULL;
+
+  /* First see whether a card is available and whether the application
+     is supported.  */
+  err = agent_card_getattr (ctrl, "$AUTHKEYID", &authkeyid);
+  if ( gpg_err_code (err) == GPG_ERR_CARD_REMOVED )
+    {
+      /* Ask for the serial number to reset the card.  */
+      err = agent_card_serialno (ctrl, &serialno);
+      if (err)
+        {
+          if (opt.verbose)
+            log_info (_("error getting serial number of card: %s\n"),
+                      gpg_strerror (err));
+          return err;
+        }
+      log_info (_("detected card with S/N: %s\n"), serialno);
+      err = agent_card_getattr (ctrl, "$AUTHKEYID", &authkeyid);
+    }
+  if (err)
+    {
+      log_error (_("error getting default authentication keyID of card: %s\n"),
+                 gpg_strerror (err));
+      xfree (serialno);
+      return err;
+    }
+
+  /* Get the S/N if we don't have it yet.  Use the fast getattr method.  */
+  if (!serialno && (err = agent_card_getattr (ctrl, "SERIALNO", &serialno)) )
+    {
+      log_error (_("error getting serial number of card: %s\n"),
+                 gpg_strerror (err));
+      xfree (authkeyid);
+      return err;
+    }
+
+  /* Read the public key.  */
+  err = agent_card_readkey (ctrl, authkeyid, &pkbuf);
+  if (err)
+    {
+      if (opt.verbose)
+        log_info (_("no suitable card key found: %s\n"), gpg_strerror (err));
+      xfree (serialno);
+      xfree (authkeyid);
+      return err;
+    }
+
+  pkbuflen = gcry_sexp_canon_len (pkbuf, 0, NULL, NULL);
+  err = gcry_sexp_sscan (&s_pk, NULL, (char*)pkbuf, pkbuflen);
+  if (err)
+    {
+      log_error ("failed to build S-Exp from received card key: %s\n",
+                 gpg_strerror (err));
+      xfree (pkbuf);
+      xfree (serialno);
+      xfree (authkeyid);
+      return err;
+    }
+
+  err = ssh_key_grip (s_pk, grip);
+  if (err)
+    {
+      log_debug ("error computing keygrip from received card key: %s\n",
+		 gcry_strerror (err));
+      xfree (pkbuf);
+      gcry_sexp_release (s_pk);
+      xfree (serialno);
+      xfree (authkeyid);
+      return err;
+    }
+
+  if ( agent_key_available (grip) )
+    {
+      /* (Shadow)-key is not available in our key storage.  */
+      unsigned char *shadow_info;
+      unsigned char *tmp;
+      
+      shadow_info = make_shadow_info (serialno, authkeyid);
+      if (!shadow_info)
+        {
+          err = gpg_error_from_errno (errno);
+          xfree (pkbuf);
+          gcry_sexp_release (s_pk);
+          xfree (serialno);
+          xfree (authkeyid);
+          return err;
+        }
+      err = agent_shadow_key (pkbuf, shadow_info, &tmp);
+      xfree (shadow_info);
+      if (err)
+        {
+          log_error (_("shadowing the key failed: %s\n"), gpg_strerror (err));
+          xfree (pkbuf);
+          gcry_sexp_release (s_pk);
+          xfree (serialno);
+          xfree (authkeyid);
+          return err;
+        }
+      xfree (pkbuf);
+      pkbuf = tmp;
+      pkbuflen = gcry_sexp_canon_len (pkbuf, 0, NULL, NULL);
+      assert (pkbuflen);
+
+      err = agent_write_private_key (grip, pkbuf, pkbuflen, 0);
+      if (err)
+        {
+          log_error (_("error writing key: %s\n"), gpg_strerror (err));
+          xfree (pkbuf);
+          gcry_sexp_release (s_pk);
+          xfree (serialno);
+          xfree (authkeyid);
+          return err;
+        }
+    }
+
+  if (cardsn)
+    {
+      char *dispsn;
+
+      /* If the card handler is able to return a short serialnumber,
+         use that one, else use the complete serialno. */
+      if (!agent_card_getattr (ctrl, "$DISPSERIALNO", &dispsn))
+        {
+          *cardsn = xtryasprintf ("cardno:%s", dispsn);
+          xfree (dispsn);
+        }
+      else
+        *cardsn = xtryasprintf ("cardno:%s", serialno);
+      if (!*cardsn)
+        {
+          err = gpg_error_from_errno (errno);
+          xfree (pkbuf);
+          gcry_sexp_release (s_pk);
+          xfree (serialno);
+          xfree (authkeyid);
+          return err;
+        }
+    }
+
+  xfree (pkbuf);
+  xfree (serialno);
+  xfree (authkeyid);
+  *r_pk = s_pk;
+  return 0;
+}
+
+
+
+
+/*
+
+  Request handler.  Each handler is provided with a CTRL context, a
+  REQUEST object and a RESPONSE object.  The actual request is to be
+  read from REQUEST, the response needs to be written to RESPONSE.
+
+*/
+
+
+/* Handler for the "request_identities" command.  */
+static gpg_error_t
+ssh_handler_request_identities (ctrl_t ctrl,
+                                estream_t request, estream_t response)
+{
+  char *key_type;
+  ssh_key_type_spec_t spec;
+  struct dirent *dir_entry;
+  char *key_directory;
+  size_t key_directory_n;
+  char *key_path;
+  unsigned char *buffer;
+  size_t buffer_n;
+  u32 key_counter;
+  estream_t key_blobs;
+  gcry_sexp_t key_secret;
+  gcry_sexp_t key_public;
+  DIR *dir;
+  gpg_error_t err;
+  int ret;
+  FILE *ctrl_fp = NULL;
+  char *cardsn;
+  gpg_error_t ret_err;
+
+  /* Prepare buffer stream.  */
+
+  key_directory = NULL;
+  key_secret = NULL;
+  key_public = NULL;
+  key_type = NULL;
+  key_path = NULL;
+  key_counter = 0;
+  buffer = NULL;
+  dir = NULL;
+  err = 0;
+
+  key_blobs = es_mopen (NULL, 0, 0, 1, NULL, NULL, "r+");
+  if (! key_blobs)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  /* Open key directory.  */
+  key_directory = make_filename (opt.homedir, GNUPG_PRIVATE_KEYS_DIR, NULL);
+  if (! key_directory)
+    {
+      err = gpg_err_code_from_errno (errno);
+      goto out;
+    }
+  key_directory_n = strlen (key_directory);
+  
+  key_path = xtrymalloc (key_directory_n + 46);
+  if (! key_path)
+    {
+      err = gpg_err_code_from_errno (errno);
+      goto out;
+    }
+
+  sprintf (key_path, "%s/", key_directory);
+  sprintf (key_path + key_directory_n + 41, ".key");
+
+  dir = opendir (key_directory);
+  if (! dir)
+    {
+      err = gpg_err_code_from_errno (errno);
+      goto out;
+    }
+
+
+
+  /* First check whether a key is currently available in the card
+     reader - this should be allowed even without being listed in
+     sshcontrol. */
+
+  if (!card_key_available (ctrl, &key_public, &cardsn))
+    {
+      err = ssh_send_key_public (key_blobs, key_public, cardsn);
+      gcry_sexp_release (key_public);
+      key_public = NULL;
+      xfree (cardsn);
+      if (err)
+        goto out;
+      
+      key_counter++;
+    }
+
+
+  /* Then look at all the registered an allowed keys. */
+
+
+  /* Fixme: We should better iterate over the control file and check
+     whether the key file is there.  This is better in resepct to
+     performance if tehre are a lot of key sin our key storage. */
+  /* FIXME: make sure that buffer gets deallocated properly.  */
+  err = open_control_file (&ctrl_fp, 0);
+  if (err)
+    goto out;
+
+  while ( (dir_entry = readdir (dir)) )
+    {
+      if ((strlen (dir_entry->d_name) == 44)
+          && (! strncmp (dir_entry->d_name + 40, ".key", 4)))
+        {
+          char hexgrip[41];
+          int disabled;
+
+          /* We do only want to return keys listed in our control
+             file. */
+          strncpy (hexgrip, dir_entry->d_name, 40);
+          hexgrip[40] = 0;
+          if ( strlen (hexgrip) != 40 )
+            continue;
+          if (search_control_file (ctrl_fp, hexgrip, &disabled)
+              || disabled)
+            continue;
+
+          strncpy (key_path + key_directory_n + 1, dir_entry->d_name, 40);
+
+          /* Read file content.  */
+          err = file_to_buffer (key_path, &buffer, &buffer_n);
+          if (err)
+            goto out;
+	      
+          err = gcry_sexp_sscan (&key_secret, NULL, (char*)buffer, buffer_n);
+          if (err)
+            goto out;
+
+          xfree (buffer);
+          buffer = NULL;
+
+          err = sexp_extract_identifier (key_secret, &key_type);
+          if (err)
+            goto out;
+
+          err = ssh_key_type_lookup (NULL, key_type, &spec);
+          if (err)
+            goto out;
+
+          xfree (key_type);
+          key_type = NULL;
+
+          err = key_secret_to_public (&key_public, spec, key_secret);
+          if (err)
+            goto out;
+
+          gcry_sexp_release (key_secret);
+          key_secret = NULL;
+	      
+          err = ssh_send_key_public (key_blobs, key_public, NULL);
+          if (err)
+            goto out;
+
+          gcry_sexp_release (key_public);
+          key_public = NULL;
+
+          key_counter++;
+        }
+    }
+  
+  ret = es_fseek (key_blobs, 0, SEEK_SET);
+  if (ret)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+ out:
+
+  /* Send response.  */
+
+  gcry_sexp_release (key_secret);
+  gcry_sexp_release (key_public);
+
+  if (! err)
+    {
+      ret_err = stream_write_byte (response, SSH_RESPONSE_IDENTITIES_ANSWER);
+      if (ret_err)
+	goto leave;
+      ret_err = stream_write_uint32 (response, key_counter);
+      if (ret_err)
+	goto leave;
+      ret_err = stream_copy (response, key_blobs);
+      if (ret_err)
+	goto leave;
+    }
+  else
+    {
+      ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+      goto leave;
+    };
+
+ leave:
+
+  if (key_blobs)
+    es_fclose (key_blobs);
+  if (dir)
+    closedir (dir);
+
+  if (ctrl_fp)
+    fclose (ctrl_fp);
+
+  free (key_directory);
+  xfree (key_path);
+  xfree (buffer);
+  xfree (key_type);
+
+  return ret_err;
+}
+
+/* This function hashes the data contained in DATA of size DATA_N
+   according to the message digest algorithm specified by MD_ALGORITHM
+   and writes the message digest to HASH, which needs to large enough
+   for the digest.  */
+static gpg_error_t
+data_hash (unsigned char *data, size_t data_n,
+	   int md_algorithm, unsigned char *hash)
+{
+  gcry_md_hash_buffer (md_algorithm, hash, data, data_n);
+
+  return 0;
+}
+
+/* This function signs the data contained in CTRL, stores the created
+   signature in newly allocated memory in SIG and it's size in SIG_N;
+   SIG_ENCODER is the signature encoder to use.  */
+static gpg_error_t
+data_sign (ctrl_t ctrl, ssh_signature_encoder_t sig_encoder,
+	   unsigned char **sig, size_t *sig_n)
+{
+  gpg_error_t err;
+  gcry_sexp_t signature_sexp = NULL;
+  estream_t stream = NULL;
+  gcry_sexp_t valuelist = NULL;
+  gcry_sexp_t sublist = NULL;
+  gcry_mpi_t sig_value = NULL;
+  unsigned char *sig_blob = NULL;
+  size_t sig_blob_n = 0;
+  char *identifier = NULL;
+  const char *identifier_raw;
+  size_t identifier_n;
+  ssh_key_type_spec_t spec;
+  int ret;
+  unsigned int i;
+  const char *elems;
+  size_t elems_n;
+  gcry_mpi_t *mpis = NULL;
+
+  *sig = NULL;
+  *sig_n = 0;
+
+  ctrl->use_auth_call = 1;
+  err = agent_pksign_do (ctrl,
+                         _("Please enter the passphrase "
+                           "for the ssh key%0A  %c"), &signature_sexp,
+                         CACHE_MODE_SSH);
+  ctrl->use_auth_call = 0;
+  if (err)
+    goto out;
+
+  valuelist = gcry_sexp_nth (signature_sexp, 1);
+  if (! valuelist)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  stream = es_mopen (NULL, 0, 0, 1, NULL, NULL, "r+");
+  if (! stream)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  identifier_raw = gcry_sexp_nth_data (valuelist, 0, &identifier_n);
+  if (! identifier_raw)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  identifier = make_cstring (identifier_raw, identifier_n);
+  if (! identifier)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  err = ssh_key_type_lookup (NULL, identifier, &spec);
+  if (err)
+    goto out;
+
+  err = stream_write_cstring (stream, spec.ssh_identifier);
+  if (err)
+    goto out;
+
+  elems = spec.elems_signature;
+  elems_n = strlen (elems);
+
+  mpis = xtrycalloc (elems_n + 1, sizeof *mpis);
+  if (!mpis)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  for (i = 0; i < elems_n; i++)
+    {
+      sublist = gcry_sexp_find_token (valuelist, spec.elems_signature + i, 1);
+      if (! sublist)
+	{
+	  err = gpg_error (GPG_ERR_INV_SEXP);
+	  break;
+	}
+
+      sig_value = gcry_sexp_nth_mpi (sublist, 1, GCRYMPI_FMT_USG);
+      if (! sig_value)
+	{
+	  err = gpg_error (GPG_ERR_INTERNAL); /* FIXME?  */
+	  break;
+	}
+      gcry_sexp_release (sublist);
+      sublist = NULL;
+
+      mpis[i] = sig_value;
+    }
+  if (err)
+    goto out;
+
+  err = (*sig_encoder) (stream, mpis);
+  if (err)
+    goto out;
+
+  sig_blob_n = es_ftell (stream);
+  if (sig_blob_n == -1)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  sig_blob = xtrymalloc (sig_blob_n);
+  if (! sig_blob)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  ret = es_fseek (stream, 0, SEEK_SET);
+  if (ret)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }    
+
+  err = stream_read_data (stream, sig_blob, sig_blob_n);
+  if (err)
+    goto out;
+  
+  *sig = sig_blob;
+  *sig_n = sig_blob_n;
+  
+ out:
+
+  if (err)
+    xfree (sig_blob);
+
+  if (stream)
+    es_fclose (stream);
+  gcry_sexp_release (valuelist);
+  gcry_sexp_release (signature_sexp);
+  gcry_sexp_release (sublist);
+  mpint_list_free (mpis);
+  xfree (identifier);
+
+  return err;
+}
+
+/* Handler for the "sign_request" command.  */
+static gpg_error_t
+ssh_handler_sign_request (ctrl_t ctrl, estream_t request, estream_t response)
+{
+  gcry_sexp_t key;
+  ssh_key_type_spec_t spec;
+  unsigned char hash[MAX_DIGEST_LEN];
+  unsigned int hash_n;
+  unsigned char key_grip[20];
+  unsigned char *key_blob;
+  u32 key_blob_size;
+  unsigned char *data;
+  unsigned char *sig;
+  size_t sig_n;
+  u32 data_size;
+  u32 flags;
+  gpg_error_t err;
+  gpg_error_t ret_err;
+
+  key_blob = NULL;
+  data = NULL;
+  sig = NULL;
+  key = NULL;
+
+  /* Receive key.  */
+  
+  err = stream_read_string (request, 0, &key_blob, &key_blob_size);
+  if (err)
+    goto out;
+
+  err = ssh_read_key_public_from_blob (key_blob, key_blob_size, &key, &spec);
+  if (err)
+    goto out;
+
+  /* Receive data to sign.  */
+  err = stream_read_string (request, 0, &data, &data_size);
+  if (err)
+    goto out;
+
+  /* FIXME?  */
+  err = stream_read_uint32 (request, &flags);
+  if (err)
+    goto out;
+
+  /* Hash data.  */
+  hash_n = gcry_md_get_algo_dlen (GCRY_MD_SHA1);
+  if (! hash_n)
+    {
+      err = gpg_error (GPG_ERR_INTERNAL);
+      goto out;
+    }
+  err = data_hash (data, data_size, GCRY_MD_SHA1, hash);
+  if (err)
+    goto out;
+
+  /* Calculate key grip.  */
+  err = ssh_key_grip (key, key_grip);
+  if (err)
+    goto out;
+
+  /* Sign data.  */
+
+  ctrl->digest.algo = GCRY_MD_SHA1;
+  memcpy (ctrl->digest.value, hash, hash_n);
+  ctrl->digest.valuelen = hash_n;
+  ctrl->digest.raw_value = ! (spec.flags & SPEC_FLAG_USE_PKCS1V2);
+  ctrl->have_keygrip = 1;
+  memcpy (ctrl->keygrip, key_grip, 20);
+
+  err = data_sign (ctrl, spec.signature_encoder, &sig, &sig_n);
+  
+ out:
+
+  /* Done.  */
+
+  if (! err)
+    {
+      ret_err = stream_write_byte (response, SSH_RESPONSE_SIGN_RESPONSE);
+      if (ret_err)
+	goto leave;
+      ret_err = stream_write_string (response, sig, sig_n);
+      if (ret_err)
+	goto leave;
+    }
+  else
+    {
+      ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+      if (ret_err)
+	goto leave;
+    }
+  
+ leave:
+
+  gcry_sexp_release (key);
+  xfree (key_blob);
+  xfree (data);
+  xfree (sig);
+
+  return ret_err;
+}
+
+/* This function extracts the comment contained in the key
+   S-Expression KEY and stores a copy in COMMENT.  Returns usual error
+   code.  */
+static gpg_error_t
+ssh_key_extract_comment (gcry_sexp_t key, char **comment)
+{
+  gcry_sexp_t comment_list;
+  char *comment_new;
+  const char *data;
+  size_t data_n;
+  gpg_error_t err;
+
+  comment_list = gcry_sexp_find_token (key, "comment", 0);
+  if (! comment_list)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+  
+  data = gcry_sexp_nth_data (comment_list, 1, &data_n);
+  if (! data)
+    {
+      err = gpg_error (GPG_ERR_INV_SEXP);
+      goto out;
+    }
+
+  comment_new = make_cstring (data, data_n);
+  if (! comment_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  *comment = comment_new;
+  err = 0;
+
+ out:
+
+  gcry_sexp_release (comment_list);
+
+  return err;
+}
+
+/* This function converts the key contained in the S-Expression KEY
+   into a buffer, which is protected by the passphrase PASSPHRASE.
+   Returns usual error code.  */
+static gpg_error_t
+ssh_key_to_protected_buffer (gcry_sexp_t key, const char *passphrase,
+			     unsigned char **buffer, size_t *buffer_n)
+{
+  unsigned char *buffer_new;
+  unsigned int buffer_new_n;
+  gpg_error_t err;
+
+  err = 0;
+  buffer_new_n = gcry_sexp_sprint (key, GCRYSEXP_FMT_CANON, NULL, 0);
+  buffer_new = xtrymalloc_secure (buffer_new_n);
+  if (! buffer_new)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+  
+  gcry_sexp_sprint (key, GCRYSEXP_FMT_CANON, buffer_new, buffer_new_n);
+  /* FIXME: guarantee?  */
+
+  err = agent_protect (buffer_new, passphrase, buffer, buffer_n);
+
+ out:
+
+  xfree (buffer_new);
+
+  return err;
+}
+
+
+
+/* Store the ssh KEY into our local key storage and protect it after
+   asking for a passphrase.  Cache that passphrase.  TTL is the
+   maximum caching time for that key.  If the key already exists in
+   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)
+{
+  gpg_error_t err;
+  unsigned char key_grip_raw[20];
+  char key_grip[41];
+  unsigned char *buffer = NULL;
+  unsigned int buffer_n;
+  char *description = NULL;
+  char *comment = NULL;
+  unsigned int i;
+  struct pin_entry_info_s *pi = NULL;
+
+  err = ssh_key_grip (key, key_grip_raw);
+  if (err)
+    goto out;
+
+  /* Check whether the key is already in our key storage.  Don't do
+     anything then.  */
+  if ( !agent_key_available (key_grip_raw) )
+    goto out; /* Yes, key is available.  */
+
+  
+  err = ssh_key_extract_comment (key, &comment);
+  if (err)
+    goto out;
+
+  if ( asprintf (&description,
+                 _("Please enter a passphrase to protect"
+                   " the received secret key%%0A"
+                   "   %s%%0A"
+                   "within gpg-agent's key storage"),
+                 comment ? comment : "?") < 0)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+
+  pi = gcry_calloc_secure (1, sizeof (*pi) + 100 + 1);
+  if (!pi)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+  pi->max_length = 100;
+  pi->max_tries = 1;
+  err = agent_askpin (ctrl, description, NULL, NULL, pi);
+  if (err)
+    goto out;
+
+  err = ssh_key_to_protected_buffer (key, pi->pin, &buffer, &buffer_n);
+  if (err)
+    goto out;
+
+  /* Store this key to our key storage.  */
+  err = agent_write_private_key (key_grip_raw, buffer, buffer_n, 0);
+  if (err)
+    goto out;
+
+  /* Cache this passphrase. */
+  for (i = 0; i < 20; i++)
+    sprintf (key_grip + 2 * i, "%02X", key_grip_raw[i]);
+
+  err = agent_put_cache (key_grip, CACHE_MODE_SSH, pi->pin, ttl);
+  if (err)
+    goto out;
+
+  /* And add an entry to the sshcontrol file.  */
+  err = add_control_entry (ctrl, key_grip, ttl);
+
+
+ out:
+  if (pi && pi->max_length)
+    wipememory (pi->pin, pi->max_length);
+  xfree (pi);
+  xfree (buffer);
+  xfree (comment);
+  free (description); /* (asprintf allocated, thus regular free.)  */
+
+  return err;
+}
+
+
+/* This function removes the key contained in the S-Expression KEY
+   from the local key storage, in case it exists there.  Returns usual
+   error code.  FIXME: this function is a stub.  */
+static gpg_error_t
+ssh_identity_drop (gcry_sexp_t key)
+{
+  unsigned char key_grip[21] = { 0 };
+  gpg_error_t err;
+
+  err = ssh_key_grip (key, key_grip);
+  if (err)
+    goto out;
+
+  key_grip[sizeof (key_grip) - 1] = 0;
+
+  /* FIXME: What to do here - forgetting the passphrase or deleting
+     the key from key cache?  */
+
+ out:
+
+  return err;
+}
+
+/* Handler for the "add_identity" command.  */
+static gpg_error_t
+ssh_handler_add_identity (ctrl_t ctrl, estream_t request, estream_t response)
+{
+  gpg_error_t ret_err;
+  gpg_error_t err;
+  gcry_sexp_t key;
+  unsigned char b;
+  int confirm;
+  int ttl;
+  
+  confirm = 0;
+  key = NULL;
+  ttl = 0;
+
+  /* FIXME?  */
+  err = ssh_receive_key (request, &key, 1, 1, NULL);
+  if (err)
+    goto out;
+
+  while (1)
+    {
+      err = stream_read_byte (request, &b);
+      if (gpg_err_code (err) == GPG_ERR_EOF)
+	{
+	  err = 0;
+	  break;
+	}
+
+      switch (b)
+	{
+	case SSH_OPT_CONSTRAIN_LIFETIME:
+	  {
+	    u32 n = 0;
+
+	    err = stream_read_uint32 (request, &n);
+	    if (! err)
+	      ttl = n;
+	    break;
+	  }
+
+	case SSH_OPT_CONSTRAIN_CONFIRM:
+	  {
+	    confirm = 1;
+	    break;
+	  }
+
+	default:
+	  /* FIXME: log/bad?  */
+	  break;
+	}
+    }
+  if (err)
+    goto out;
+
+  /* FIXME: are constraints used correctly?  */
+
+  err = ssh_identity_register (ctrl, key, ttl);
+
+ out:
+
+  gcry_sexp_release (key);
+
+  if (! err)
+    ret_err = stream_write_byte (response, SSH_RESPONSE_SUCCESS);
+  else
+    ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+
+  return ret_err;
+}
+
+/* Handler for the "remove_identity" command.  */
+static gpg_error_t
+ssh_handler_remove_identity (ctrl_t ctrl,
+			     estream_t request, estream_t response)
+{
+  unsigned char *key_blob;
+  u32 key_blob_size;
+  gcry_sexp_t key;
+  gpg_error_t ret_err;
+  gpg_error_t err;
+
+  /* Receive key.  */
+
+  key_blob = NULL;
+  key = NULL;
+  
+  err = stream_read_string (request, 0, &key_blob, &key_blob_size);
+  if (err)
+    goto out;
+
+  err = ssh_read_key_public_from_blob (key_blob, key_blob_size, &key, NULL);
+  if (err)
+    goto out;
+  
+  err = ssh_identity_drop (key);
+
+ out:
+
+  xfree (key_blob);
+  gcry_sexp_release (key);
+
+  if (! err)
+    ret_err = stream_write_byte (response, SSH_RESPONSE_SUCCESS);
+  else
+    ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+
+  return ret_err;
+}
+
+/* FIXME: stub function.  Actually useful?  */
+static gpg_error_t
+ssh_identities_remove_all (void)
+{
+  gpg_error_t err;
+
+  err = 0;
+
+  /* FIXME: shall we remove _all_ cache entries or only those
+     registered through the ssh emulation?  */
+  
+  return err;
+}
+
+/* Handler for the "remove_all_identities" command.  */
+static gpg_error_t
+ssh_handler_remove_all_identities (ctrl_t ctrl,
+				   estream_t request, estream_t response)
+{
+  gpg_error_t ret_err;
+  gpg_error_t err;
+  
+  err = ssh_identities_remove_all ();
+
+  if (! err)
+    ret_err = stream_write_byte (response, SSH_RESPONSE_SUCCESS);
+  else
+    ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+
+  return ret_err;
+}
+
+/* Lock agent?  FIXME: stub function.  */
+static gpg_error_t
+ssh_lock (void)
+{
+  gpg_error_t err;
+
+  /* FIXME */
+  log_error ("ssh-agent's lock command is not implemented\n");
+  err = 0;
+
+  return err;
+}
+
+/* Unock agent?  FIXME: stub function.  */
+static gpg_error_t
+ssh_unlock (void)
+{
+  gpg_error_t err;
+
+  log_error ("ssh-agent's unlock command is not implemented\n");
+  err = 0;
+
+  return err;
+}
+
+/* Handler for the "lock" command.  */
+static gpg_error_t
+ssh_handler_lock (ctrl_t ctrl, estream_t request, estream_t response)
+{
+  gpg_error_t ret_err;
+  gpg_error_t err;
+  
+  err = ssh_lock ();
+
+  if (! err)
+    ret_err = stream_write_byte (response, SSH_RESPONSE_SUCCESS);
+  else
+    ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+
+  return ret_err;
+}
+
+/* Handler for the "unlock" command.  */
+static gpg_error_t
+ssh_handler_unlock (ctrl_t ctrl, estream_t request, estream_t response)
+{
+  gpg_error_t ret_err;
+  gpg_error_t err;
+  
+  err = ssh_unlock ();
+
+  if (! err)
+    ret_err = stream_write_byte (response, SSH_RESPONSE_SUCCESS);
+  else
+    ret_err = stream_write_byte (response, SSH_RESPONSE_FAILURE);
+
+  return ret_err;
+}
+
+
+
+/* Return the request specification for the request identified by TYPE
+   or NULL in case the requested request specification could not be
+   found.  */
+static ssh_request_spec_t *
+request_spec_lookup (int type)
+{
+  ssh_request_spec_t *spec;
+  unsigned int i;
+
+  for (i = 0; i < DIM (request_specs); i++)
+    if (request_specs[i].type == type)
+      break;
+  if (i == DIM (request_specs))
+    {
+      log_info ("ssh request %u is not supported\n", type);
+      spec = NULL;
+    }
+  else
+    spec = request_specs + i;
+
+  return spec;
+}
+
+/* Process a single request.  The request is read from and the
+   response is written to STREAM_SOCK.  Uses CTRL as context.  Returns
+   zero in case of success, non zero in case of failure.  */
+static int
+ssh_request_process (ctrl_t ctrl, estream_t stream_sock)
+{
+  ssh_request_spec_t *spec;
+  estream_t response;
+  estream_t request;
+  unsigned char request_type;
+  gpg_error_t err;
+  int send_err;
+  int ret;
+  unsigned char *request_data;
+  u32 request_data_size;
+  u32 response_size;
+
+  request_data = NULL;
+  response = NULL;
+  request = NULL;
+  send_err = 0;
+
+  /* Create memory streams for request/response data.  The entire
+     request will be stored in secure memory, since it might contain
+     secret key material.  The response does not have to be stored in
+     secure memory, since we never give out secret keys. 
+
+     Note: we only have little secure memory, but there is NO
+     possibility of DoS here; only trusted clients are allowed to
+     connect to the agent.  What could happen is that the agent
+     returns out-of-secure-memory errors on requests in case the
+     agent's owner floods his own agent with many large messages.
+     -moritz */
+
+  /* Retrieve request.  */
+  err = stream_read_string (stream_sock, 1, &request_data, &request_data_size);
+  if (err)
+    goto out;
+
+  if (opt.verbose > 1)
+    log_info ("received ssh request of length %u\n",
+              (unsigned int)request_data_size);
+
+  if (! request_data_size)
+    {
+      send_err = 1;
+      goto out;
+      /* Broken request; FIXME.  */
+    }
+
+  request_type = request_data[0];
+  spec = request_spec_lookup (request_type);
+  if (! spec)
+    {
+      send_err = 1;
+      goto out;
+      /* Unknown request; FIXME.  */
+    }
+
+  if (spec->secret_input)
+    request = es_mopen (NULL, 0, 0, 1, realloc_secure, gcry_free, "r+");
+  else
+    request = es_mopen (NULL, 0, 0, 1, gcry_realloc, gcry_free, "r+");
+  if (! request)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+  ret = es_setvbuf (request, NULL, _IONBF, 0);
+  if (ret)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+  err = stream_write_data (request, request_data + 1, request_data_size - 1);
+  if (err)
+    goto out;
+  es_rewind (request);
+
+  response = es_mopen (NULL, 0, 0, 1, NULL, NULL, "r+");
+  if (! response)
+    {
+      err = gpg_error_from_errno (errno);
+      goto out;
+    }
+
+  if (opt.verbose)
+    log_info ("ssh request handler for %s (%u) started\n",
+	       spec->identifier, spec->type);
+
+  err = (*spec->handler) (ctrl, request, response);
+
+  if (opt.verbose)
+    {
+      if (err)
+        log_info ("ssh request handler for %s (%u) failed: %s\n",
+                  spec->identifier, spec->type, gpg_strerror (err));
+      else
+        log_info ("ssh request handler for %s (%u) ready\n",
+                  spec->identifier, spec->type);
+    }
+
+  if (err)
+    {
+      send_err = 1;
+      goto out;
+    }
+
+  response_size = es_ftell (response);
+  if (opt.verbose > 1)
+    log_info ("sending ssh response of length %u\n",
+              (unsigned int)response_size);
+
+  err = es_fseek (response, 0, SEEK_SET);
+  if (err)
+    {
+      send_err = 1;
+      goto out;
+    }
+
+  err = stream_write_uint32 (stream_sock, response_size);
+  if (err)
+    {
+      send_err = 1;
+      goto out;
+    }
+
+  err = stream_copy (stream_sock, response);
+  if (err)
+    goto out;
+
+  err = es_fflush (stream_sock);
+  if (err)
+    goto out;
+
+ out:
+
+  if (err && es_feof (stream_sock))
+    log_error ("error occured while processing request: %s\n",
+	       gpg_strerror (err));
+
+  if (send_err)
+    {
+      if (opt.verbose > 1)
+        log_info ("sending ssh error response\n");
+      err = stream_write_uint32 (stream_sock, 1);
+      if (err)
+	goto leave;
+      err = stream_write_byte (stream_sock, SSH_RESPONSE_FAILURE);
+      if (err)
+	goto leave;
+    }
+
+ leave:
+
+  if (request)
+    es_fclose (request);
+  if (response)
+    es_fclose (response);
+  xfree (request_data);		/* FIXME?  */
+
+  return !!err;
+}
+
+/* Start serving client on SOCK_CLIENT.  */
+void
+start_command_handler_ssh (int sock_client)
+{
+  struct server_control_s ctrl;
+  estream_t stream_sock;
+  gpg_error_t err;
+  int ret;
+
+  /* Setup control structure.  */
+
+  memset (&ctrl, 0, sizeof (ctrl));
+  agent_init_default_ctrl (&ctrl);
+  ctrl.connection_fd = sock_client;
+
+  /* Because the ssh protocol does not send us information about the
+     the current TTY setting, we resort here to use those from startup
+     or those explictly set.  */
+  if (!ctrl.display && opt.startup_display)
+    ctrl.display = strdup (opt.startup_display);
+  if (!ctrl.ttyname && opt.startup_ttyname)
+    ctrl.ttyname = strdup (opt.startup_ttyname);
+  if (!ctrl.ttytype && opt.startup_ttytype)
+    ctrl.ttytype = strdup (opt.startup_ttytype);
+  if (!ctrl.lc_ctype && opt.startup_lc_ctype)
+    ctrl.lc_ctype = strdup (opt.startup_lc_ctype);
+  if (!ctrl.lc_messages && opt.startup_lc_messages)
+    ctrl.lc_messages = strdup (opt.startup_lc_messages);
+
+
+  /* Create stream from socket.  */
+  stream_sock = es_fdopen (sock_client, "r+");
+  if (!stream_sock)
+    {
+      err = gpg_error_from_errno (errno);
+      log_error (_("failed to create stream from socket: %s\n"),
+		 gpg_strerror (err));
+      goto out;
+    }
+  /* We have to disable the estream buffering, because the estream
+     core doesn't know about secure memory.  */
+  ret = es_setvbuf (stream_sock, NULL, _IONBF, 0);
+  if (ret)
+    {
+      err = gpg_error_from_errno (errno);
+      log_error (_("failed to disable buffering "
+                   "on socket stream: %s\n"), gpg_strerror (err));
+      goto out;
+    }
+
+  /* Main processing loop. */
+  while ( !ssh_request_process (&ctrl, stream_sock) )
+    ;
+
+  /* Reset the SCD in case it has been used. */
+  agent_reset_scd (&ctrl);
+
+
+ out:
+  if (stream_sock)
+    es_fclose (stream_sock);
+
+  free (ctrl.display);
+  free (ctrl.ttyname);
+  free (ctrl.ttytype);
+  free (ctrl.lc_ctype);
+  free (ctrl.lc_messages);
+}