Adding upstream version 2.2.40.upstream/2.2.40

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2380 insertions, 0 deletions

diff --git a/sm/certchain.c b/sm/certchain.c
new file mode 100644
index 0000000..d2a1800
--- /dev/null
+++ b/sm/certchain.c
@@ -0,0 +1,2380 @@
+/* certchain.c - certificate chain validation
+ * Copyright (C) 2001, 2002, 2003, 2004, 2005,
+ *               2006, 2007, 2008, 2011 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 3 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, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <time.h>
+#include <stdarg.h>
+#include <assert.h>
+
+#include "gpgsm.h"
+#include <gcrypt.h>
+#include <ksba.h>
+
+#include "keydb.h"
+#include "../kbx/keybox.h" /* for KEYBOX_FLAG_* */
+#include "../common/i18n.h"
+#include "../common/tlv.h"
+
+
+/* The OID for the authorityInfoAccess's caIssuers.  */
+static const char oidstr_caIssuers[] = "1.3.6.1.5.5.7.48.2";
+
+
+/* Object to keep track of certain root certificates. */
+struct marktrusted_info_s
+{
+  struct marktrusted_info_s *next;
+  unsigned char fpr[20];
+};
+static struct marktrusted_info_s *marktrusted_info;
+
+
+/* While running the validation function we want to keep track of the
+   certificates in the chain.  This type is used for that.  */
+struct chain_item_s
+{
+  struct chain_item_s *next;
+  ksba_cert_t cert;      /* The certificate.  */
+  int is_root;           /* The certificate is the root certificate.  */
+};
+typedef struct chain_item_s *chain_item_t;
+
+
+static int is_root_cert (ksba_cert_t cert,
+                         const char *issuerdn, const char *subjectdn);
+static int get_regtp_ca_info (ctrl_t ctrl, ksba_cert_t cert, int *chainlen);
+
+
+/* This function returns true if we already asked during this session
+   whether the root certificate CERT shall be marked as trusted.  */
+static int
+already_asked_marktrusted (ksba_cert_t cert)
+{
+  unsigned char fpr[20];
+  struct marktrusted_info_s *r;
+
+  gpgsm_get_fingerprint (cert, GCRY_MD_SHA1, fpr, NULL);
+  /* No context switches in the loop! */
+  for (r=marktrusted_info; r; r= r->next)
+    if (!memcmp (r->fpr, fpr, 20))
+      return 1;
+  return 0;
+}
+
+/* Flag certificate CERT as already asked whether it shall be marked
+   as trusted.  */
+static void
+set_already_asked_marktrusted (ksba_cert_t cert)
+{
+ unsigned char fpr[20];
+ struct marktrusted_info_s *r;
+
+ gpgsm_get_fingerprint (cert, GCRY_MD_SHA1, fpr, NULL);
+ for (r=marktrusted_info; r; r= r->next)
+   if (!memcmp (r->fpr, fpr, 20))
+     return; /* Already marked. */
+ r = xtrycalloc (1, sizeof *r);
+ if (!r)
+   return;
+ memcpy (r->fpr, fpr, 20);
+ r->next = marktrusted_info;
+ marktrusted_info = r;
+}
+
+/* If LISTMODE is true, print FORMAT using LISTMODE to FP.  If
+   LISTMODE is false, use the string to print an log_info or, if
+   IS_ERROR is true, and log_error. */
+static void
+do_list (int is_error, int listmode, estream_t fp, const char *format, ...)
+{
+  va_list arg_ptr;
+
+  va_start (arg_ptr, format) ;
+  if (listmode)
+    {
+      if (fp)
+        {
+          es_fputs ("  [", fp);
+          es_vfprintf (fp, format, arg_ptr);
+          es_fputs ("]\n", fp);
+        }
+    }
+  else
+    {
+      log_logv (is_error? GPGRT_LOG_ERROR: GPGRT_LOG_INFO, format, arg_ptr);
+      log_printf ("\n");
+    }
+  va_end (arg_ptr);
+}
+
+/* Return 0 if A and B are equal. */
+static int
+compare_certs (ksba_cert_t a, ksba_cert_t b)
+{
+  const unsigned char *img_a, *img_b;
+  size_t len_a, len_b;
+
+  img_a = ksba_cert_get_image (a, &len_a);
+  if (!img_a)
+    return 1;
+  img_b = ksba_cert_get_image (b, &len_b);
+  if (!img_b)
+    return 1;
+  return !(len_a == len_b && !memcmp (img_a, img_b, len_a));
+}
+
+
+/* Return true if CERT has the validityModel extensions and defines
+   the use of the chain model.  */
+static int
+has_validation_model_chain (ksba_cert_t cert, int listmode, estream_t listfp)
+{
+  gpg_error_t err;
+  int idx, yes;
+  const char *oid;
+  size_t off, derlen, objlen, hdrlen;
+  const unsigned char *der;
+  int class, tag, constructed, ndef;
+  char *oidbuf;
+
+  for (idx=0; !(err=ksba_cert_get_extension (cert, idx,
+                                             &oid, NULL, &off, &derlen));idx++)
+    if (!strcmp (oid, "1.3.6.1.4.1.8301.3.5") )
+      break;
+  if (err)
+    return 0; /* Not found.  */
+  der = ksba_cert_get_image (cert, NULL);
+  if (!der)
+    {
+      err = gpg_error (GPG_ERR_INV_OBJ); /* Oops  */
+      goto leave;
+    }
+  der += off;
+
+  err = parse_ber_header (&der, &derlen, &class, &tag, &constructed,
+                          &ndef, &objlen, &hdrlen);
+  if (!err && (objlen > derlen || tag != TAG_SEQUENCE))
+    err = gpg_error (GPG_ERR_INV_OBJ);
+  if (err)
+    goto leave;
+  derlen = objlen;
+  err = parse_ber_header (&der, &derlen, &class, &tag, &constructed,
+                          &ndef, &objlen, &hdrlen);
+  if (!err && (objlen > derlen || tag != TAG_OBJECT_ID))
+    err = gpg_error (GPG_ERR_INV_OBJ);
+  if (err)
+    goto leave;
+  oidbuf = ksba_oid_to_str (der, objlen);
+  if (!oidbuf)
+    {
+      err = gpg_error_from_syserror ();
+      goto leave;
+    }
+
+  if (opt.verbose)
+    do_list (0, listmode, listfp,
+             _("validation model requested by certificate: %s"),
+              !strcmp (oidbuf, "1.3.6.1.4.1.8301.3.5.1")? _("chain") :
+              !strcmp (oidbuf, "1.3.6.1.4.1.8301.3.5.2")? _("shell") :
+              /* */                                       oidbuf);
+  yes = !strcmp (oidbuf, "1.3.6.1.4.1.8301.3.5.1");
+  ksba_free (oidbuf);
+  return yes;
+
+
+ leave:
+  log_error ("error parsing validityModel: %s\n", gpg_strerror (err));
+  return 0;
+}
+
+
+
+static int
+unknown_criticals (ksba_cert_t cert, int listmode, estream_t fp)
+{
+  static const char *known[] = {
+    "2.5.29.15", /* keyUsage */
+    "2.5.29.17", /* subjectAltName
+                    Japanese DoCoMo certs mark them as critical.  PKIX
+                    only requires them as critical if subjectName is
+                    empty.  I don't know whether our code gracefully
+                    handles such empry subjectNames but that is
+                    another story. */
+    "2.5.29.19", /* basic Constraints */
+    "2.5.29.32", /* certificatePolicies */
+    "2.5.29.37", /* extendedKeyUsage - handled by certlist.c */
+    "1.3.6.1.4.1.8301.3.5", /* validityModel - handled here. */
+    NULL
+  };
+  int rc = 0, i, idx, crit;
+  const char *oid;
+  gpg_error_t err;
+  int unsupported;
+  strlist_t sl;
+
+  for (idx=0; !(err=ksba_cert_get_extension (cert, idx,
+                                             &oid, &crit, NULL, NULL));idx++)
+    {
+      if (!crit)
+        continue;
+      for (i=0; known[i] && strcmp (known[i],oid); i++)
+        ;
+      unsupported = !known[i];
+
+      /* If this critical extension is not supported.  Check the list
+         of to be ignored extensions to see whether we claim that it
+         is supported.  */
+      if (unsupported && opt.ignored_cert_extensions)
+        {
+          for (sl=opt.ignored_cert_extensions;
+               sl && strcmp (sl->d, oid); sl = sl->next)
+            ;
+          if (sl)
+            unsupported = 0;
+        }
+      if (unsupported)
+        {
+          do_list (1, listmode, fp,
+                   _("critical certificate extension %s is not supported"),
+                   oid);
+          rc = gpg_error (GPG_ERR_UNSUPPORTED_CERT);
+        }
+    }
+  /* We ignore the error codes EOF as well as no-value. The later will
+     occur for certificates with no extensions at all. */
+  if (err
+      && gpg_err_code (err) != GPG_ERR_EOF
+      && gpg_err_code (err) != GPG_ERR_NO_VALUE)
+    rc = err;
+
+  return rc;
+}
+
+
+/* Check whether CERT is an allowed certificate.  This requires that
+   CERT matches all requirements for such a CA, i.e. the
+   BasicConstraints extension.  The function returns 0 on success and
+   the allowed length of the chain at CHAINLEN. */
+static int
+allowed_ca (ctrl_t ctrl,
+            ksba_cert_t cert, int *chainlen, int listmode, estream_t fp)
+{
+  gpg_error_t err;
+  int flag;
+
+  err = ksba_cert_is_ca (cert, &flag, chainlen);
+  if (err)
+    return err;
+  if (!flag)
+    {
+      if (get_regtp_ca_info (ctrl, cert, chainlen))
+        {
+          /* Note that dirmngr takes a different way to cope with such
+             certs. */
+          return 0; /* RegTP issued certificate. */
+        }
+
+      do_list (1, listmode, fp,_("issuer certificate is not marked as a CA"));
+      return gpg_error (GPG_ERR_BAD_CA_CERT);
+    }
+  return 0;
+}
+
+
+static int
+check_cert_policy (ksba_cert_t cert, int listmode, estream_t fplist)
+{
+  gpg_error_t err;
+  char *policies;
+  estream_t fp;
+  int any_critical;
+
+  err = ksba_cert_get_cert_policies (cert, &policies);
+  if (gpg_err_code (err) == GPG_ERR_NO_DATA)
+    return 0; /* No policy given. */
+  if (err)
+    return err;
+
+  /* STRING is a line delimited list of certificate policies as stored
+     in the certificate.  The line itself is colon delimited where the
+     first field is the OID of the policy and the second field either
+     N or C for normal or critical extension */
+
+  if (opt.verbose > 1 && !listmode)
+    log_info ("certificate's policy list: %s\n", policies);
+
+  /* The check is very minimal but won't give false positives */
+  any_critical = !!strstr (policies, ":C");
+
+  if (!opt.policy_file)
+    {
+      xfree (policies);
+      if (any_critical)
+        {
+          do_list (1, listmode, fplist,
+                   _("critical marked policy without configured policies"));
+          return gpg_error (GPG_ERR_NO_POLICY_MATCH);
+        }
+      return 0;
+    }
+
+  fp = es_fopen (opt.policy_file, "r");
+  if (!fp)
+    {
+      if (opt.verbose || errno != ENOENT)
+        log_info (_("failed to open '%s': %s\n"),
+                  opt.policy_file, strerror (errno));
+      xfree (policies);
+      /* With no critical policies this is only a warning */
+      if (!any_critical)
+        {
+          if (!opt.quiet)
+            do_list (0, listmode, fplist,
+                     _("Note: non-critical certificate policy not allowed"));
+          return 0;
+        }
+      do_list (1, listmode, fplist,
+               _("certificate policy not allowed"));
+      return gpg_error (GPG_ERR_NO_POLICY_MATCH);
+    }
+
+  for (;;)
+    {
+      int c;
+      char *p, line[256];
+      char *haystack, *allowed;
+
+      /* read line */
+      do
+        {
+          if (!es_fgets (line, DIM(line)-1, fp) )
+            {
+              gpg_error_t tmperr = gpg_error_from_syserror ();
+
+              xfree (policies);
+              if (es_feof (fp))
+                {
+                  es_fclose (fp);
+                  /* With no critical policies this is only a warning */
+                  if (!any_critical)
+                    {
+                      do_list (0, listmode, fplist,
+                     _("Note: non-critical certificate policy not allowed"));
+                      return 0;
+                    }
+                  do_list (1, listmode, fplist,
+                           _("certificate policy not allowed"));
+                  return gpg_error (GPG_ERR_NO_POLICY_MATCH);
+                }
+              es_fclose (fp);
+              return tmperr;
+            }
+
+          if (!*line || line[strlen(line)-1] != '\n')
+            {
+              /* eat until end of line */
+              while ((c = es_getc (fp)) != EOF && c != '\n')
+                ;
+              es_fclose (fp);
+              xfree (policies);
+              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 == '#');
+
+      /* Parse line.  Note that the line has always a LF and spacep
+         does not consider a LF a space.  Thus strpbrk will always
+         succeed.  */
+      for (allowed=line; spacep (allowed); allowed++)
+        ;
+      p = strpbrk (allowed, " :\n");
+      if (!*p || p == allowed)
+        {
+          es_fclose (fp);
+          xfree (policies);
+          return gpg_error (GPG_ERR_CONFIGURATION);
+        }
+      *p = 0; /* strip the rest of the line */
+      /* See whether we find ALLOWED (which is an OID) in POLICIES */
+      for (haystack=policies; (p=strstr (haystack, allowed)); haystack = p+1)
+        {
+          if ( !(p == policies || p[-1] == '\n') )
+            continue; /* Does not match the begin of a line. */
+          if (p[strlen (allowed)] != ':')
+            continue; /* The length does not match. */
+          /* Yep - it does match so return okay. */
+          es_fclose (fp);
+          xfree (policies);
+          return 0;
+        }
+    }
+}
+
+
+/* Helper function for find_up.  This resets the key handle and search
+   for an issuer ISSUER with a subjectKeyIdentifier of KEYID.  Returns
+   0 on success or -1 when not found. */
+static int
+find_up_search_by_keyid (ctrl_t ctrl, KEYDB_HANDLE kh,
+                         const char *issuer, ksba_sexp_t keyid)
+{
+  int rc;
+  ksba_cert_t cert = NULL;
+  ksba_sexp_t subj = NULL;
+  ksba_isotime_t not_before, not_after, last_not_before, ne_last_not_before;
+  ksba_cert_t found_cert = NULL;
+  ksba_cert_t ne_found_cert = NULL;
+
+  keydb_search_reset (kh);
+  while (!(rc = keydb_search_subject (ctrl, kh, issuer)))
+    {
+      ksba_cert_release (cert); cert = NULL;
+      rc = keydb_get_cert (kh, &cert);
+      if (rc)
+        {
+          log_error ("keydb_get_cert() failed: rc=%d\n", rc);
+          rc = -1;
+          goto leave;
+        }
+      xfree (subj);
+      if (!ksba_cert_get_subj_key_id (cert, NULL, &subj))
+        {
+          if (!cmp_simple_canon_sexp (keyid, subj))
+            {
+              /* Found matching cert. */
+              rc = ksba_cert_get_validity (cert, 0, not_before);
+              if (!rc)
+                rc = ksba_cert_get_validity (cert, 1, not_after);
+              if (rc)
+                {
+                  log_error ("keydb_get_validity() failed: rc=%d\n", rc);
+                  rc = -1;
+                  goto leave;
+                }
+
+              if (!found_cert
+                  || strcmp (last_not_before, not_before) < 0)
+                {
+                  /* This certificate is the first one found or newer
+                   * than the previous one.  This copes with
+                   * re-issuing CA certificates while keeping the same
+                   * key information.  */
+                  gnupg_copy_time (last_not_before, not_before);
+                  ksba_cert_release (found_cert);
+                  ksba_cert_ref ((found_cert = cert));
+                  keydb_push_found_state (kh);
+                }
+
+              if (*not_after && strcmp (ctrl->current_time, not_after) > 0 )
+                ; /* CERT has expired - don't consider it.  */
+              else if (!ne_found_cert
+                       || strcmp (ne_last_not_before, not_before) < 0)
+                {
+                  /* This certificate is the first non-expired one
+                   * found or newer than the previous non-expired one.  */
+                  gnupg_copy_time (ne_last_not_before, not_before);
+                  ksba_cert_release (ne_found_cert);
+                  ksba_cert_ref ((ne_found_cert = cert));
+                }
+            }
+        }
+    }
+
+  if (!found_cert)
+    goto leave;
+
+  /* Take the last saved one.  Note that push/pop_found_state are
+   * misnomers because there is no stack of states.  Renaming them to
+   * save/restore_found_state would be better.  */
+  keydb_pop_found_state (kh);
+  rc = 0;  /* Ignore EOF or other error after the first cert.  */
+
+  /* We need to consider some corner cases.  It is possible that we
+   * have a long term certificate (e.g. valid from 2008 to 2033) as
+   * well as a re-issued (i.e. using the same key material) short term
+   * certificate (say from 2016 to 2019).  Using the short term
+   * certificate is the proper solution.  But we need to take care if
+   * there is no re-issued new short term certificate (e.g. from 2020
+   * to 2023) available.  In that case it is better to use the long
+   * term certificate which is still valid.  The code may run into
+   * minor problems in the case of the chain validation mode.  Given
+   * that this corner case is due to non-diligent PKI management we
+   * ignore this problem.  */
+
+  /* The most common case is that the found certificate is not expired
+   * and thus identical to the one found from the list of non-expired
+   * certs.  We can stop here.  */
+  if (found_cert == ne_found_cert)
+    goto leave;
+  /* If we do not have a non expired certificate the actual cert is
+   * expired and we can also stop here.  */
+  if (!ne_found_cert)
+    goto leave;
+  /* Now we need to see whether the found certificate is expired and
+   * only in this case we return the certificate found in the list of
+   * non-expired certs.  */
+  rc = ksba_cert_get_validity (found_cert, 1, not_after);
+  if (rc)
+    {
+      log_error ("keydb_get_validity() failed: rc=%d\n", rc);
+      rc = -1;
+      goto leave;
+    }
+  if (*not_after && strcmp (ctrl->current_time, not_after) > 0 )
+    { /* CERT has expired.  Use the NE_FOUND_CERT.  Because we have no
+       * found state for this we need to search for it again.  */
+      unsigned char fpr[20];
+
+      gpgsm_get_fingerprint (ne_found_cert, GCRY_MD_SHA1, fpr, NULL);
+      keydb_search_reset (kh);
+      rc = keydb_search_fpr (ctrl, kh, fpr);
+      if (rc)
+        {
+          log_error ("keydb_search_fpr() failed: rc=%d\n", rc);
+          rc = -1;
+          goto leave;
+        }
+      /* Ready.  The NE_FOUND_CERT is availabale via keydb_get_cert.  */
+    }
+
+ leave:
+  ksba_cert_release (found_cert);
+  ksba_cert_release (ne_found_cert);
+  ksba_cert_release (cert);
+  xfree (subj);
+  return rc? -1:0;
+}
+
+
+struct find_up_store_certs_s
+{
+  ctrl_t ctrl;
+  int count;
+  unsigned int want_fpr:1;
+  unsigned int got_fpr:1;
+  unsigned char fpr[20];
+};
+
+static void
+find_up_store_certs_cb (void *cb_value, ksba_cert_t cert)
+{
+  struct find_up_store_certs_s *parm = cb_value;
+
+  if (keydb_store_cert (parm->ctrl, cert, 1, NULL))
+    log_error ("error storing issuer certificate as ephemeral\n");
+  else if (parm->want_fpr && !parm->got_fpr)
+    {
+      if (!gpgsm_get_fingerprint (cert, 0, parm->fpr, NULL))
+        log_error (_("failed to get the fingerprint\n"));
+      else
+        parm->got_fpr = 1;
+    }
+  parm->count++;
+}
+
+
+/* Helper for find_up().  Locate the certificate for ISSUER using an
+   external lookup.  KH is the keydb context we are currently using.
+   On success 0 is returned and the certificate may be retrieved from
+   the keydb using keydb_get_cert().  KEYID is the keyIdentifier from
+   the AKI or NULL.  */
+static int
+find_up_external (ctrl_t ctrl, KEYDB_HANDLE kh,
+                  const char *issuer, ksba_sexp_t keyid)
+{
+  int rc;
+  strlist_t names = NULL;
+  struct find_up_store_certs_s find_up_store_certs_parm;
+  char *pattern;
+  const char *s;
+
+  find_up_store_certs_parm.ctrl = ctrl;
+  find_up_store_certs_parm.want_fpr = 0;
+  find_up_store_certs_parm.got_fpr = 0;
+  find_up_store_certs_parm.count = 0;
+
+  if (opt.verbose)
+    log_info (_("looking up issuer at external location\n"));
+  /* The Dirmngr process is confused about unknown attributes.  As a
+     quick and ugly hack we locate the CN and use the issuer string
+     starting at this attribite.  Fixme: we should have far better
+     parsing for external lookups in the Dirmngr. */
+  s = strstr (issuer, "CN=");
+  if (!s || s == issuer || s[-1] != ',')
+    s = issuer;
+  pattern = xtrymalloc (strlen (s)+2);
+  if (!pattern)
+    return gpg_error_from_syserror ();
+  strcpy (stpcpy (pattern, "/"), s);
+  add_to_strlist (&names, pattern);
+  xfree (pattern);
+
+  rc = gpgsm_dirmngr_lookup (ctrl, names, NULL, 0, find_up_store_certs_cb,
+                             &find_up_store_certs_parm);
+  free_strlist (names);
+
+  if (opt.verbose)
+    log_info (_("number of issuers matching: %d\n"),
+              find_up_store_certs_parm.count);
+  if (rc)
+    {
+      log_error ("external key lookup failed: %s\n", gpg_strerror (rc));
+      rc = -1;
+    }
+  else if (!find_up_store_certs_parm.count)
+    rc = -1;
+  else
+    {
+      int old;
+      /* The issuers are currently stored in the ephemeral key DB, so
+         we temporary switch to ephemeral mode. */
+      old = keydb_set_ephemeral (kh, 1);
+      if (keyid)
+        rc = find_up_search_by_keyid (ctrl, kh, issuer, keyid);
+      else
+        {
+          keydb_search_reset (kh);
+          rc = keydb_search_subject (ctrl, kh, issuer);
+        }
+      keydb_set_ephemeral (kh, old);
+    }
+  return rc;
+}
+
+
+/* Helper for find_up().  Locate the certificate for CERT using the
+ * caIssuer from the authorityInfoAccess.  KH is the keydb context we
+ * are currently using.  On success 0 is returned and the certificate
+ * may be retrieved from the keydb using keydb_get_cert().  If no
+ * suitable authorityInfoAccess is encoded in the certificate
+ * GPG_ERR_NOT_FOUND is returned. */
+static gpg_error_t
+find_up_via_auth_info_access (ctrl_t ctrl, KEYDB_HANDLE kh, ksba_cert_t cert)
+{
+  gpg_error_t err;
+  struct find_up_store_certs_s find_up_store_certs_parm;
+  char *url, *ldapurl;
+  int idx, i;
+  char *oid;
+  ksba_name_t name;
+
+  find_up_store_certs_parm.ctrl = ctrl;
+  find_up_store_certs_parm.want_fpr = 1;
+  find_up_store_certs_parm.got_fpr = 0;
+  find_up_store_certs_parm.count = 0;
+
+  /* Find suitable URLs; if there is a http scheme we prefer that.  */
+  url = ldapurl = NULL;
+  for (idx=0;
+       !url && !(err = ksba_cert_get_authority_info_access (cert, idx,
+                                                            &oid, &name));
+       idx++)
+    {
+      if (!strcmp (oid, oidstr_caIssuers))
+        {
+          for (i=0; !url && ksba_name_enum (name, i); i++)
+            {
+              char *p = ksba_name_get_uri (name, i);
+              if (p)
+                {
+                  if (!strncmp (p, "http:", 5) || !strncmp (p, "https:", 6))
+                    url = p;
+                  else if (ldapurl)
+                    xfree (p); /* We already got one.  */
+                  else if (!strncmp (p, "ldap:",5) || !strncmp (p, "ldaps:",6))
+                    ldapurl = p;
+                }
+              else
+                xfree (p);
+            }
+        }
+      ksba_name_release (name);
+      ksba_free (oid);
+    }
+  if (err && gpg_err_code (err) != GPG_ERR_EOF)
+    {
+      log_error (_("can't get authorityInfoAccess: %s\n"), gpg_strerror (err));
+      return err;
+    }
+  if (!url && ldapurl)
+    {
+      /* No HTTP scheme; fallback to LDAP if available.  */
+      url = ldapurl;
+      ldapurl = NULL;
+    }
+  xfree (ldapurl);
+  if (!url)
+    return gpg_error (GPG_ERR_NOT_FOUND);
+
+  if (opt.verbose)
+    log_info ("looking up issuer via authorityInfoAccess.caIssuers\n");
+
+  err = gpgsm_dirmngr_lookup (ctrl, NULL, url, 0, find_up_store_certs_cb,
+                              &find_up_store_certs_parm);
+
+  /* Although we might receive several certificates we use only the
+   * first one.  Or more exacty the first one for which we retrieved
+   * the fingerprint.  */
+  if (opt.verbose)
+    log_info ("number of caIssuers found: %d\n",
+              find_up_store_certs_parm.count);
+  if (err)
+    {
+      log_error ("external URL lookup failed: %s\n", gpg_strerror (err));
+      err = gpg_error (GPG_ERR_NOT_FOUND);
+    }
+  else if (!find_up_store_certs_parm.got_fpr)
+    err = gpg_error (GPG_ERR_NOT_FOUND);
+  else
+    {
+      int old;
+      /* The retrieved certificates are currently stored in the
+       * ephemeral key DB, so we temporary switch to ephemeral
+       * mode. */
+      old = keydb_set_ephemeral (kh, 1);
+      keydb_search_reset (kh);
+      err = keydb_search_fpr (ctrl, kh, find_up_store_certs_parm.fpr);
+      keydb_set_ephemeral (kh, old);
+    }
+
+  return err;
+}
+
+
+/* Helper for find_up().  Ask the dirmngr for the certificate for
+   ISSUER with optional SERIALNO.  KH is the keydb context we are
+   currently using.  With SUBJECT_MODE set, ISSUER is searched as the
+   subject.  On success 0 is returned and the certificate is available
+   in the ephemeral DB.  */
+static int
+find_up_dirmngr (ctrl_t ctrl, KEYDB_HANDLE kh,
+                 ksba_sexp_t serialno, const char *issuer, int subject_mode)
+{
+  int rc;
+  strlist_t names = NULL;
+  struct find_up_store_certs_s find_up_store_certs_parm;
+  char *pattern;
+
+  (void)kh;
+
+  find_up_store_certs_parm.ctrl = ctrl;
+  find_up_store_certs_parm.count = 0;
+
+  if (opt.verbose)
+    log_info (_("looking up issuer from the Dirmngr cache\n"));
+  if (subject_mode)
+    {
+      pattern = xtrymalloc (strlen (issuer)+2);
+      if (pattern)
+        strcpy (stpcpy (pattern, "/"), issuer);
+    }
+  else if (serialno)
+    pattern = gpgsm_format_sn_issuer (serialno, issuer);
+  else
+    {
+      pattern = xtrymalloc (strlen (issuer)+3);
+      if (pattern)
+        strcpy (stpcpy (pattern, "#/"), issuer);
+    }
+  if (!pattern)
+    return gpg_error_from_syserror ();
+  add_to_strlist (&names, pattern);
+  xfree (pattern);
+
+  rc = gpgsm_dirmngr_lookup (ctrl, names, NULL, 1, find_up_store_certs_cb,
+                             &find_up_store_certs_parm);
+  free_strlist (names);
+
+  if (opt.verbose)
+    log_info (_("number of matching certificates: %d\n"),
+              find_up_store_certs_parm.count);
+  if (rc && !opt.quiet)
+    log_info (_("dirmngr cache-only key lookup failed: %s\n"),
+              gpg_strerror (rc));
+  return (!rc && find_up_store_certs_parm.count)? 0 : -1;
+}
+
+
+
+/* Locate issuing certificate for CERT. ISSUER is the name of the
+   issuer used as a fallback if the other methods don't work.  If
+   FIND_NEXT is true, the function shall return the next possible
+   issuer.  The certificate itself is not directly returned but a
+   keydb_get_cert on the keydb context KH will return it.  Returns 0
+   on success, -1 if not found or an error code.  */
+static int
+find_up (ctrl_t ctrl, KEYDB_HANDLE kh,
+         ksba_cert_t cert, const char *issuer, int find_next)
+{
+  ksba_name_t authid;
+  ksba_sexp_t authidno;
+  ksba_sexp_t keyid;
+  int rc = -1;
+
+  if (DBG_X509)
+    log_debug ("looking for parent certificate\n");
+  if (!ksba_cert_get_auth_key_id (cert, &keyid, &authid, &authidno))
+    {
+      const char *s = ksba_name_enum (authid, 0);
+      if (s && *authidno)
+        {
+          rc = keydb_search_issuer_sn (ctrl, kh, s, authidno);
+          if (rc)
+            keydb_search_reset (kh);
+
+          if (!rc && DBG_X509)
+            log_debug ("  found via authid and sn+issuer\n");
+
+          /* In case of an error, try to get the certificate from the
+             dirmngr.  That is done by trying to put that certifcate
+             into the ephemeral DB and let the code below do the
+             actual retrieve.  Thus there is no error checking.
+             Skipped in find_next mode as usual. */
+          if (rc == -1 && !find_next)
+            find_up_dirmngr (ctrl, kh, authidno, s, 0);
+
+          /* In case of an error try the ephemeral DB.  We can't do
+             that in find_next mode because we can't keep the search
+             state then. */
+          if (rc == -1 && !find_next)
+            {
+              int old = keydb_set_ephemeral (kh, 1);
+              if (!old)
+                {
+                  rc = keydb_search_issuer_sn (ctrl, kh, s, authidno);
+                  if (rc)
+                    keydb_search_reset (kh);
+
+                  if (!rc && DBG_X509)
+                    log_debug ("  found via authid and sn+issuer (ephem)\n");
+                }
+              keydb_set_ephemeral (kh, old);
+            }
+          if (rc)
+            rc = -1; /* Need to make sure to have this error code. */
+        }
+
+      if (rc == -1 && keyid && !find_next)
+        {
+          /* Not found by AKI.issuer_sn.  Lets try the AKI.ki
+             instead. Loop over all certificates with that issuer as
+             subject and stop for the one with a matching
+             subjectKeyIdentifier. */
+          /* Fixme: Should we also search in the dirmngr?  */
+          rc = find_up_search_by_keyid (ctrl, kh, issuer, keyid);
+          if (!rc && DBG_X509)
+            log_debug ("  found via authid and keyid\n");
+          if (rc)
+            {
+              int old = keydb_set_ephemeral (kh, 1);
+              if (!old)
+                rc = find_up_search_by_keyid (ctrl, kh, issuer, keyid);
+              if (!rc && DBG_X509)
+                log_debug ("  found via authid and keyid (ephem)\n");
+              keydb_set_ephemeral (kh, old);
+            }
+          if (rc)
+            rc = -1; /* Need to make sure to have this error code. */
+        }
+
+      /* If we still didn't found it, try to find it via the subject
+         from the dirmngr-cache.  */
+      if (rc == -1 && !find_next)
+        {
+          if (!find_up_dirmngr (ctrl, kh, NULL, issuer, 1))
+            {
+              int old = keydb_set_ephemeral (kh, 1);
+              if (keyid)
+                rc = find_up_search_by_keyid (ctrl, kh, issuer, keyid);
+              else
+                {
+                  keydb_search_reset (kh);
+                  rc = keydb_search_subject (ctrl, kh, issuer);
+                }
+              keydb_set_ephemeral (kh, old);
+            }
+          if (rc)
+            rc = -1; /* Need to make sure to have this error code. */
+
+          if (!rc && DBG_X509)
+            log_debug ("  found via authid and issuer from dirmngr cache\n");
+        }
+
+      /* If we still didn't found it, try an external lookup.  */
+      if (rc == -1 && !find_next && !ctrl->offline)
+        {
+          /* We allow AIA also if CRLs are enabled; both can be used
+           * as a web bug so it does not make sense to not use AIA if
+           * CRL checks are enabled.  */
+          if ((opt.auto_issuer_key_retrieve || !opt.no_crl_check)
+              && !find_up_via_auth_info_access (ctrl, kh, cert))
+            {
+              if (DBG_X509)
+                log_debug ("  found via authorityInfoAccess.caIssuers\n");
+              rc = 0;
+            }
+          else if (opt.auto_issuer_key_retrieve)
+            {
+              rc = find_up_external (ctrl, kh, issuer, keyid);
+              if (!rc && DBG_X509)
+                log_debug ("  found via authid and external lookup\n");
+            }
+        }
+
+
+      /* Print a note so that the user does not feel too helpless when
+         an issuer certificate was found and gpgsm prints BAD
+         signature because it is not the correct one. */
+      if (rc == -1 && opt.quiet)
+        ;
+      else if (rc == -1)
+        {
+          log_info ("%sissuer certificate ", find_next?"next ":"");
+          if (keyid)
+            {
+              log_printf ("{");
+              gpgsm_dump_serial (keyid);
+              log_printf ("} ");
+            }
+          if (authidno)
+            {
+              log_printf ("(#");
+              gpgsm_dump_serial (authidno);
+              log_printf ("/");
+              gpgsm_dump_string (s);
+              log_printf (") ");
+            }
+          log_printf ("not found using authorityKeyIdentifier\n");
+        }
+      else if (rc)
+        log_error ("failed to find authorityKeyIdentifier: rc=%d\n", rc);
+      xfree (keyid);
+      ksba_name_release (authid);
+      xfree (authidno);
+    }
+
+  if (rc) /* Not found via authorithyKeyIdentifier, try regular issuer name. */
+    rc = keydb_search_subject (ctrl, kh, issuer);
+  if (rc == -1 && !find_next)
+    {
+      int old;
+
+      /* Also try to get it from the Dirmngr cache.  The function
+         merely puts it into the ephemeral database.  */
+      find_up_dirmngr (ctrl, kh, NULL, issuer, 0);
+
+      /* Not found, let us see whether we have one in the ephemeral key DB. */
+      old = keydb_set_ephemeral (kh, 1);
+      if (!old)
+        {
+          keydb_search_reset (kh);
+          rc = keydb_search_subject (ctrl, kh, issuer);
+        }
+      keydb_set_ephemeral (kh, old);
+
+      if (!rc && DBG_X509)
+        log_debug ("  found via issuer\n");
+    }
+
+  /* Still not found.  If enabled, try an external lookup.  */
+  if (rc == -1 && !find_next && !ctrl->offline)
+    {
+      if ((opt.auto_issuer_key_retrieve || !opt.no_crl_check)
+          && !find_up_via_auth_info_access (ctrl, kh, cert))
+        {
+          if (DBG_X509)
+            log_debug ("  found via authorityInfoAccess.caIssuers\n");
+          rc = 0;
+        }
+      else if (opt.auto_issuer_key_retrieve)
+        {
+          rc = find_up_external (ctrl, kh, issuer, NULL);
+          if (!rc && DBG_X509)
+            log_debug ("  found via issuer and external lookup\n");
+        }
+    }
+
+  return rc;
+}
+
+
+/* Return the next certificate up in the chain starting at START.
+   Returns -1 when there are no more certificates. */
+int
+gpgsm_walk_cert_chain (ctrl_t ctrl, ksba_cert_t start, ksba_cert_t *r_next)
+{
+  int rc = 0;
+  char *issuer = NULL;
+  char *subject = NULL;
+  KEYDB_HANDLE kh = keydb_new ();
+
+  *r_next = NULL;
+  if (!kh)
+    {
+      log_error (_("failed to allocate keyDB handle\n"));
+      rc = gpg_error (GPG_ERR_GENERAL);
+      goto leave;
+    }
+
+  issuer = ksba_cert_get_issuer (start, 0);
+  subject = ksba_cert_get_subject (start, 0);
+  if (!issuer)
+    {
+      log_error ("no issuer found in certificate\n");
+      rc = gpg_error (GPG_ERR_BAD_CERT);
+      goto leave;
+    }
+  if (!subject)
+    {
+      log_error ("no subject found in certificate\n");
+      rc = gpg_error (GPG_ERR_BAD_CERT);
+      goto leave;
+    }
+
+  if (is_root_cert (start, issuer, subject))
+    {
+      rc = -1; /* we are at the root */
+      goto leave;
+    }
+
+  rc = find_up (ctrl, kh, start, issuer, 0);
+  if (rc)
+    {
+      /* It is quite common not to have a certificate, so better don't
+         print an error here.  */
+      if (rc != -1 && opt.verbose > 1)
+        log_error ("failed to find issuer's certificate: rc=%d\n", rc);
+      rc = gpg_error (GPG_ERR_MISSING_ISSUER_CERT);
+      goto leave;
+    }
+
+  rc = keydb_get_cert (kh, r_next);
+  if (rc)
+    {
+      log_error ("keydb_get_cert() failed: rc=%d\n", rc);
+      rc = gpg_error (GPG_ERR_GENERAL);
+    }
+
+ leave:
+  xfree (issuer);
+  xfree (subject);
+  keydb_release (kh);
+  return rc;
+}
+
+
+/* Helper for gpgsm_is_root_cert.  This one is used if the subject and
+   issuer DNs are already known.  */
+static int
+is_root_cert (ksba_cert_t cert, const char *issuerdn, const char *subjectdn)
+{
+  gpg_error_t err;
+  int result = 0;
+  ksba_sexp_t serialno;
+  ksba_sexp_t ak_keyid;
+  ksba_name_t ak_name;
+  ksba_sexp_t ak_sn;
+  const char *ak_name_str;
+  ksba_sexp_t subj_keyid = NULL;
+
+  if (!issuerdn || !subjectdn)
+    return 0;  /* No.  */
+
+  if (strcmp (issuerdn, subjectdn))
+    return 0;  /* No.  */
+
+  err = ksba_cert_get_auth_key_id (cert, &ak_keyid, &ak_name, &ak_sn);
+  if (err)
+    {
+      if (gpg_err_code (err) == GPG_ERR_NO_DATA)
+        return 1; /* Yes. Without a authorityKeyIdentifier this needs
+                     to be the Root certifcate (our trust anchor).  */
+      log_error ("error getting authorityKeyIdentifier: %s\n",
+                 gpg_strerror (err));
+      return 0; /* Well, it is broken anyway.  Return No. */
+    }
+
+  serialno = ksba_cert_get_serial (cert);
+  if (!serialno)
+    {
+      log_error ("error getting serialno: %s\n", gpg_strerror (err));
+      goto leave;
+    }
+
+  /* Check whether the auth name's matches the issuer name+sn.  If
+     that is the case this is a root certificate.  */
+  ak_name_str = ksba_name_enum (ak_name, 0);
+  if (ak_name_str
+      && !strcmp (ak_name_str, issuerdn)
+      && !cmp_simple_canon_sexp (ak_sn, serialno))
+    {
+      result = 1;  /* Right, CERT is self-signed.  */
+      goto leave;
+    }
+
+  /* Similar for the ak_keyid. */
+  if (ak_keyid && !ksba_cert_get_subj_key_id (cert, NULL, &subj_keyid)
+      && !cmp_simple_canon_sexp (ak_keyid, subj_keyid))
+    {
+      result = 1;  /* Right, CERT is self-signed.  */
+      goto leave;
+    }
+
+
+ leave:
+  ksba_free (subj_keyid);
+  ksba_free (ak_keyid);
+  ksba_name_release (ak_name);
+  ksba_free (ak_sn);
+  ksba_free (serialno);
+  return result;
+}
+
+
+
+/* Check whether the CERT is a root certificate.  Returns True if this
+   is the case. */
+int
+gpgsm_is_root_cert (ksba_cert_t cert)
+{
+  char *issuer;
+  char *subject;
+  int yes;
+
+  issuer = ksba_cert_get_issuer (cert, 0);
+  subject = ksba_cert_get_subject (cert, 0);
+  yes = is_root_cert (cert, issuer, subject);
+  xfree (issuer);
+  xfree (subject);
+  return yes;
+}
+
+
+/* This is a helper for gpgsm_validate_chain. */
+static gpg_error_t
+is_cert_still_valid (ctrl_t ctrl, int force_ocsp, int lm, estream_t fp,
+                     ksba_cert_t subject_cert, ksba_cert_t issuer_cert,
+                     int *any_revoked, int *any_no_crl, int *any_crl_too_old)
+{
+  gpg_error_t err;
+
+  if (ctrl->offline || (opt.no_crl_check && !ctrl->use_ocsp))
+    {
+      audit_log_ok (ctrl->audit, AUDIT_CRL_CHECK,
+                    gpg_error (GPG_ERR_NOT_ENABLED));
+      return 0;
+    }
+
+
+  if (!(force_ocsp || ctrl->use_ocsp)
+      && !opt.enable_issuer_based_crl_check)
+    {
+      err = ksba_cert_get_crl_dist_point (subject_cert, 0, NULL, NULL, NULL);
+      if (gpg_err_code (err) == GPG_ERR_EOF)
+        {
+          /* No DP specified in the certificate.  Thus the CA does not
+           * consider a CRL useful and the user of the certificate
+           * also does not consider this to be a critical thing.  In
+           * this case we can conclude that the certificate shall not
+           * be revocable.  Note that we reach this point here only if
+           * no OCSP responder shall be used.  */
+          audit_log_ok (ctrl->audit, AUDIT_CRL_CHECK, gpg_error (GPG_ERR_TRUE));
+          return 0;
+        }
+    }
+
+  err = gpgsm_dirmngr_isvalid (ctrl,
+                               subject_cert, issuer_cert,
+                               force_ocsp? 2 : !!ctrl->use_ocsp);
+  audit_log_ok (ctrl->audit, AUDIT_CRL_CHECK, err);
+
+  if (err)
+    {
+      if (!lm)
+        gpgsm_cert_log_name (NULL, subject_cert);
+      switch (gpg_err_code (err))
+        {
+        case GPG_ERR_CERT_REVOKED:
+          do_list (1, lm, fp, _("certificate has been revoked"));
+          *any_revoked = 1;
+          /* Store that in the keybox so that key listings are able to
+             return the revoked flag.  We don't care about error,
+             though. */
+          keydb_set_cert_flags (ctrl, subject_cert, 1, KEYBOX_FLAG_VALIDITY, 0,
+                                ~0, VALIDITY_REVOKED);
+          break;
+
+        case GPG_ERR_NO_CRL_KNOWN:
+          do_list (1, lm, fp, _("no CRL found for certificate"));
+          *any_no_crl = 1;
+          break;
+
+        case GPG_ERR_NO_DATA:
+          do_list (1, lm, fp, _("the status of the certificate is unknown"));
+          *any_no_crl = 1;
+          break;
+
+        case GPG_ERR_CRL_TOO_OLD:
+          do_list (1, lm, fp, _("the available CRL is too old"));
+          if (!lm)
+            log_info (_("please make sure that the "
+                        "\"dirmngr\" is properly installed\n"));
+          *any_crl_too_old = 1;
+          break;
+
+        default:
+          do_list (1, lm, fp, _("checking the CRL failed: %s"),
+                   gpg_strerror (err));
+          return err;
+        }
+    }
+  return 0;
+}
+
+
+/* Helper for gpgsm_validate_chain to check the validity period of
+   SUBJECT_CERT.  The caller needs to pass EXPTIME which will be
+   updated to the nearest expiration time seen.  A DEPTH of 0 indicates
+   the target certificate, -1 the final root certificate and other
+   values intermediate certificates. */
+static gpg_error_t
+check_validity_period (ksba_isotime_t current_time,
+                       ksba_cert_t subject_cert,
+                       ksba_isotime_t exptime,
+                       int listmode, estream_t listfp, int depth)
+{
+  gpg_error_t err;
+  ksba_isotime_t not_before, not_after;
+
+  err = ksba_cert_get_validity (subject_cert, 0, not_before);
+  if (!err)
+    err = ksba_cert_get_validity (subject_cert, 1, not_after);
+  if (err)
+    {
+      do_list (1, listmode, listfp,
+               _("certificate with invalid validity: %s"), gpg_strerror (err));
+      return gpg_error (GPG_ERR_BAD_CERT);
+    }
+
+  if (*not_after)
+    {
+      if (!*exptime)
+        gnupg_copy_time (exptime, not_after);
+      else if (strcmp (not_after, exptime) < 0 )
+        gnupg_copy_time (exptime, not_after);
+    }
+
+  if (*not_before && strcmp (current_time, not_before) < 0 )
+    {
+      do_list (1, listmode, listfp,
+               depth ==  0 ? _("certificate not yet valid") :
+               depth == -1 ? _("root certificate not yet valid") :
+               /* other */   _("intermediate certificate not yet valid"));
+      if (!listmode)
+        {
+          log_info ("  (valid from ");
+          dump_isotime (not_before);
+          log_printf (")\n");
+        }
+      return gpg_error (GPG_ERR_CERT_TOO_YOUNG);
+    }
+
+  if (*not_after && strcmp (current_time, not_after) > 0 )
+    {
+      do_list (opt.ignore_expiration?0:1, listmode, listfp,
+               depth == 0  ? _("certificate has expired") :
+               depth == -1 ? _("root certificate has expired") :
+               /* other  */  _("intermediate certificate has expired"));
+      if (!listmode)
+        {
+          log_info ("  (expired at ");
+          dump_isotime (not_after);
+          log_printf (")\n");
+        }
+      if (opt.ignore_expiration)
+        log_info ("WARNING: ignoring expiration\n");
+      else
+        return gpg_error (GPG_ERR_CERT_EXPIRED);
+    }
+
+  return 0;
+}
+
+/* This is a variant of check_validity_period used with the chain
+   model.  The dextra contraint here is that notBefore and notAfter
+   must exists and if the additional argument CHECK_TIME is given this
+   time is used to check the validity period of SUBJECT_CERT.  */
+static gpg_error_t
+check_validity_period_cm (ksba_isotime_t current_time,
+                          ksba_isotime_t check_time,
+                          ksba_cert_t subject_cert,
+                          ksba_isotime_t exptime,
+                          int listmode, estream_t listfp, int depth)
+{
+  gpg_error_t err;
+  ksba_isotime_t not_before, not_after;
+
+  err = ksba_cert_get_validity (subject_cert, 0, not_before);
+  if (!err)
+    err = ksba_cert_get_validity (subject_cert, 1, not_after);
+  if (err)
+    {
+      do_list (1, listmode, listfp,
+               _("certificate with invalid validity: %s"), gpg_strerror (err));
+      return gpg_error (GPG_ERR_BAD_CERT);
+    }
+  if (!*not_before || !*not_after)
+    {
+      do_list (1, listmode, listfp,
+               _("required certificate attributes missing: %s%s%s"),
+               !*not_before? "notBefore":"",
+               (!*not_before && !*not_after)? ", ":"",
+               !*not_before? "notAfter":"");
+      return gpg_error (GPG_ERR_BAD_CERT);
+    }
+  if (strcmp (not_before, not_after) > 0 )
+    {
+      do_list (1, listmode, listfp,
+               _("certificate with invalid validity"));
+      log_info ("  (valid from ");
+      dump_isotime (not_before);
+      log_printf (" expired at ");
+      dump_isotime (not_after);
+      log_printf (")\n");
+      return gpg_error (GPG_ERR_BAD_CERT);
+    }
+
+  if (!*exptime)
+    gnupg_copy_time (exptime, not_after);
+  else if (strcmp (not_after, exptime) < 0 )
+    gnupg_copy_time (exptime, not_after);
+
+  if (strcmp (current_time, not_before) < 0 )
+    {
+      do_list (1, listmode, listfp,
+               depth ==  0 ? _("certificate not yet valid") :
+               depth == -1 ? _("root certificate not yet valid") :
+               /* other */   _("intermediate certificate not yet valid"));
+      if (!listmode)
+        {
+          log_info ("  (valid from ");
+          dump_isotime (not_before);
+          log_printf (")\n");
+        }
+      return gpg_error (GPG_ERR_CERT_TOO_YOUNG);
+    }
+
+  if (*check_time
+      && (strcmp (check_time, not_before) < 0
+          || strcmp (check_time, not_after) > 0))
+    {
+      /* Note that we don't need a case for the root certificate
+         because its own consitency has already been checked.  */
+      do_list(opt.ignore_expiration?0:1, listmode, listfp,
+              depth == 0 ?
+              _("signature not created during lifetime of certificate") :
+              depth == 1 ?
+              _("certificate not created during lifetime of issuer") :
+              _("intermediate certificate not created during lifetime "
+                "of issuer"));
+      if (!listmode)
+        {
+          log_info (depth== 0? _("  (  signature created at ") :
+                    /* */      _("  (certificate created at ") );
+          dump_isotime (check_time);
+          log_printf (")\n");
+          log_info (depth==0? _("  (certificate valid from ") :
+                    /* */     _("  (     issuer valid from ") );
+          dump_isotime (not_before);
+          log_info (" to ");
+          dump_isotime (not_after);
+          log_printf (")\n");
+        }
+      if (opt.ignore_expiration)
+        log_info ("WARNING: ignoring expiration\n");
+      else
+        return gpg_error (GPG_ERR_CERT_EXPIRED);
+    }
+
+  return 0;
+}
+
+
+
+/* Ask the user whether he wants to mark the certificate CERT trusted.
+   Returns true if the CERT is the trusted.  We also check whether the
+   agent is at all enabled to allow marktrusted and don't call it in
+   this session again if it is not.  */
+static int
+ask_marktrusted (ctrl_t ctrl, ksba_cert_t cert, int listmode)
+{
+  static int no_more_questions;
+  int rc;
+  char *fpr;
+  int success = 0;
+
+  fpr = gpgsm_get_fingerprint_string (cert, GCRY_MD_SHA1);
+  log_info (_("fingerprint=%s\n"), fpr? fpr : "?");
+  xfree (fpr);
+
+  if (no_more_questions)
+    rc = gpg_error (GPG_ERR_NOT_SUPPORTED);
+  else
+    rc = gpgsm_agent_marktrusted (ctrl, cert);
+  if (!rc)
+    {
+      log_info (_("root certificate has now been marked as trusted\n"));
+      success = 1;
+    }
+  else if (!listmode)
+    {
+      gpgsm_dump_cert ("issuer", cert);
+      log_info ("after checking the fingerprint, you may want "
+                "to add it manually to the list of trusted certificates.\n");
+    }
+
+  if (gpg_err_code (rc) == GPG_ERR_NOT_SUPPORTED)
+    {
+      if (!no_more_questions)
+        log_info (_("interactive marking as trusted "
+                    "not enabled in gpg-agent\n"));
+      no_more_questions = 1;
+    }
+  else if (gpg_err_code (rc) == GPG_ERR_CANCELED)
+    {
+      log_info (_("interactive marking as trusted "
+                  "disabled for this session\n"));
+      no_more_questions = 1;
+    }
+  else
+    set_already_asked_marktrusted (cert);
+
+  return success;
+}
+
+
+
+
+/* Validate a chain and optionally return the nearest expiration time
+   in R_EXPTIME. With LISTMODE set to 1 a special listmode is
+   activated where only information about the certificate is printed
+   to LISTFP and no output is send to the usual log stream.  If
+   CHECKTIME_ARG is set, it is used only in the chain model instead of the
+   current time.
+
+   Defined flag bits
+
+   VALIDATE_FLAG_NO_DIRMNGR  - Do not do any dirmngr isvalid checks.
+   VALIDATE_FLAG_CHAIN_MODEL - Check according to chain model.
+   VALIDATE_FLAG_STEED       - Check according to the STEED model.
+*/
+static int
+do_validate_chain (ctrl_t ctrl, ksba_cert_t cert, ksba_isotime_t checktime_arg,
+                   ksba_isotime_t r_exptime,
+                   int listmode, estream_t listfp, unsigned int flags,
+                   struct rootca_flags_s *rootca_flags)
+{
+  int rc = 0, depth, maxdepth;
+  char *issuer = NULL;
+  char *subject = NULL;
+  KEYDB_HANDLE kh = NULL;
+  ksba_cert_t subject_cert = NULL, issuer_cert = NULL;
+  ksba_isotime_t current_time;
+  ksba_isotime_t check_time;
+  ksba_isotime_t exptime;
+  int any_expired = 0;
+  int any_revoked = 0;
+  int any_no_crl = 0;
+  int any_crl_too_old = 0;
+  int any_no_policy_match = 0;
+  int is_qualified = -1; /* Indicates whether the certificate stems
+                            from a qualified root certificate.
+                            -1 = unknown, 0 = no, 1 = yes. */
+  chain_item_t chain = NULL; /* A list of all certificates in the chain.  */
+
+
+  gnupg_get_isotime (current_time);
+  gnupg_copy_time (ctrl->current_time, current_time);
+
+  if ( (flags & VALIDATE_FLAG_CHAIN_MODEL) )
+    {
+      if (!strcmp (checktime_arg, "19700101T000000"))
+        {
+          do_list (1, listmode, listfp,
+                   _("WARNING: creation time of signature not known - "
+                     "assuming current time"));
+          gnupg_copy_time (check_time, current_time);
+        }
+      else
+        gnupg_copy_time (check_time, checktime_arg);
+    }
+  else
+    *check_time = 0;
+
+  if (r_exptime)
+    *r_exptime = 0;
+  *exptime = 0;
+
+  if (opt.no_chain_validation && !listmode)
+    {
+      log_info ("WARNING: bypassing certificate chain validation\n");
+      return 0;
+    }
+
+  kh = keydb_new ();
+  if (!kh)
+    {
+      log_error (_("failed to allocate keyDB handle\n"));
+      rc = gpg_error (GPG_ERR_GENERAL);
+      goto leave;
+    }
+
+  if (DBG_X509 && !listmode)
+    gpgsm_dump_cert ("target", cert);
+
+  subject_cert = cert;
+  ksba_cert_ref (subject_cert);
+  maxdepth = 50;
+  depth = 0;
+
+  for (;;)
+    {
+      int is_root;
+      gpg_error_t istrusted_rc = -1;
+
+      /* Put the certificate on our list.  */
+      {
+        chain_item_t ci;
+
+        ci = xtrycalloc (1, sizeof *ci);
+        if (!ci)
+          {
+            rc = gpg_error_from_syserror ();
+            goto leave;
+          }
+        ksba_cert_ref (subject_cert);
+        ci->cert = subject_cert;
+        ci->next = chain;
+        chain = ci;
+      }
+
+      xfree (issuer);
+      xfree (subject);
+      issuer = ksba_cert_get_issuer (subject_cert, 0);
+      subject = ksba_cert_get_subject (subject_cert, 0);
+
+      if (!issuer)
+        {
+          do_list (1, listmode, listfp,  _("no issuer found in certificate"));
+          rc = gpg_error (GPG_ERR_BAD_CERT);
+          goto leave;
+        }
+
+
+      /* Is this a self-issued certificate (i.e. the root certificate)?  */
+      is_root = is_root_cert (subject_cert, issuer, subject);
+      if (is_root)
+        {
+          chain->is_root = 1;
+          /* Check early whether the certificate is listed as trusted.
+             We used to do this only later but changed it to call the
+             check right here so that we can access special flags
+             associated with that specific root certificate.  */
+          if (gpgsm_cert_has_well_known_private_key (subject_cert))
+            {
+              memset (rootca_flags, 0, sizeof *rootca_flags);
+              istrusted_rc = ((flags & VALIDATE_FLAG_STEED)
+                              ? 0 : gpg_error (GPG_ERR_NOT_TRUSTED));
+            }
+          else
+            istrusted_rc = gpgsm_agent_istrusted (ctrl, subject_cert, NULL,
+                                                  rootca_flags);
+          audit_log_cert (ctrl->audit, AUDIT_ROOT_TRUSTED,
+                          subject_cert, istrusted_rc);
+          /* If the chain model extended attribute is used, make sure
+             that our chain model flag is set. */
+          if (!(flags & VALIDATE_FLAG_STEED)
+              && has_validation_model_chain (subject_cert, listmode, listfp))
+            rootca_flags->chain_model = 1;
+        }
+
+
+      /* Check the validity period. */
+      if ( (flags & VALIDATE_FLAG_CHAIN_MODEL) )
+        rc = check_validity_period_cm (current_time, check_time, subject_cert,
+                                       exptime, listmode, listfp,
+                                       (depth && is_root)? -1: depth);
+      else
+        rc = check_validity_period (current_time, subject_cert,
+                                    exptime, listmode, listfp,
+                                    (depth && is_root)? -1: depth);
+      if (gpg_err_code (rc) == GPG_ERR_CERT_EXPIRED)
+        any_expired = 1;
+      else if (rc)
+        goto leave;
+
+
+      /* Assert that we understand all critical extensions. */
+      rc = unknown_criticals (subject_cert, listmode, listfp);
+      if (rc)
+        goto leave;
+
+      /* Do a policy check. */
+      if (!opt.no_policy_check)
+        {
+          rc = check_cert_policy (subject_cert, listmode, listfp);
+          if (gpg_err_code (rc) == GPG_ERR_NO_POLICY_MATCH)
+            {
+              any_no_policy_match = 1;
+              rc = 1;  /* Be on the safe side and set RC.  */
+            }
+          else if (rc)
+            goto leave;
+        }
+
+
+      /* If this is the root certificate we are at the end of the chain.  */
+      if (is_root)
+        {
+          if (!istrusted_rc)
+            ; /* No need to check the certificate for a trusted one. */
+          else if (gpgsm_check_cert_sig (subject_cert, subject_cert) )
+            {
+              /* We only check the signature if the certificate is not
+                 trusted for better diagnostics. */
+              do_list (1, listmode, listfp,
+                       _("self-signed certificate has a BAD signature"));
+              if (DBG_X509)
+                {
+                  gpgsm_dump_cert ("self-signing cert", subject_cert);
+                }
+              rc = gpg_error (depth? GPG_ERR_BAD_CERT_CHAIN
+                                   : GPG_ERR_BAD_CERT);
+              goto leave;
+            }
+          if (!rootca_flags->relax)
+            {
+              rc = allowed_ca (ctrl, subject_cert, NULL, listmode, listfp);
+              if (rc)
+                goto leave;
+            }
+
+
+          /* Set the flag for qualified signatures.  This flag is
+             deduced from a list of root certificates allowed for
+             qualified signatures. */
+          if (is_qualified == -1 && !(flags & VALIDATE_FLAG_STEED))
+            {
+              gpg_error_t err;
+              size_t buflen;
+              char buf[1];
+
+              if (!ksba_cert_get_user_data (cert, "is_qualified",
+                                            &buf, sizeof (buf),
+                                            &buflen) && buflen)
+                {
+                  /* We already checked this for this certificate,
+                     thus we simply take it from the user data. */
+                  is_qualified = !!*buf;
+                }
+              else
+                {
+                  /* Need to consult the list of root certificates for
+                     qualified signatures. */
+                  err = gpgsm_is_in_qualified_list (ctrl, subject_cert, NULL);
+                  if (!err)
+                    is_qualified = 1;
+                  else if ( gpg_err_code (err) == GPG_ERR_NOT_FOUND)
+                    is_qualified = 0;
+                  else
+                    log_error ("checking the list of qualified "
+                               "root certificates failed: %s\n",
+                               gpg_strerror (err));
+                  if ( is_qualified != -1 )
+                    {
+                      /* Cache the result but don't care too much
+                         about an error. */
+                      buf[0] = !!is_qualified;
+                      err = ksba_cert_set_user_data (subject_cert,
+                                                     "is_qualified", buf, 1);
+                      if (err)
+                        log_error ("set_user_data(is_qualified) failed: %s\n",
+                                   gpg_strerror (err));
+                    }
+                }
+            }
+
+
+          /* Act on the check for a trusted root certificates. */
+          rc = istrusted_rc;
+          if (!rc)
+            ;
+          else if (gpg_err_code (rc) == GPG_ERR_NOT_TRUSTED)
+            {
+              do_list (0, listmode, listfp,
+                       _("root certificate is not marked trusted"));
+              /* If we already figured out that the certificate is
+                 expired it does not make much sense to ask the user
+                 whether they want to trust the root certificate.  We
+                 should do this only if the certificate under question
+                 will then be usable.  If the certificate has a well
+                 known private key asking the user does not make any
+                 sense.  */
+              if ( !any_expired
+                   && !gpgsm_cert_has_well_known_private_key (subject_cert)
+                   && (!listmode || !already_asked_marktrusted (subject_cert))
+                   && ask_marktrusted (ctrl, subject_cert, listmode) )
+                rc = 0;
+            }
+          else
+            {
+              log_error (_("checking the trust list failed: %s\n"),
+                         gpg_strerror (rc));
+            }
+
+          if (rc)
+            goto leave;
+
+          /* Check for revocations etc. */
+          if ((flags & VALIDATE_FLAG_NO_DIRMNGR))
+            ;
+          else if ((flags & VALIDATE_FLAG_STEED))
+            ; /* Fixme: check revocations via DNS.  */
+          else if (opt.no_trusted_cert_crl_check || rootca_flags->relax)
+            ;
+          else
+            rc = is_cert_still_valid (ctrl,
+                                      (flags & VALIDATE_FLAG_CHAIN_MODEL),
+                                      listmode, listfp,
+                                      subject_cert, subject_cert,
+                                      &any_revoked, &any_no_crl,
+                                      &any_crl_too_old);
+          if (rc)
+            goto leave;
+
+          break;  /* Okay: a self-signed certicate is an end-point. */
+        } /* End is_root.  */
+
+
+      /* Take care that the chain does not get too long. */
+      if ((depth+1) > maxdepth)
+        {
+          do_list (1, listmode, listfp, _("certificate chain too long\n"));
+          rc = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+          goto leave;
+        }
+
+      /* Find the next cert up the tree. */
+      keydb_search_reset (kh);
+      rc = find_up (ctrl, kh, subject_cert, issuer, 0);
+      if (rc)
+        {
+          if (rc == -1)
+            {
+              do_list (0, listmode, listfp, _("issuer certificate not found"));
+              if (!listmode)
+                {
+                  log_info ("issuer certificate: #/");
+                  gpgsm_dump_string (issuer);
+                  log_printf ("\n");
+                }
+            }
+          else
+            log_error ("failed to find issuer's certificate: rc=%d\n", rc);
+          rc = gpg_error (GPG_ERR_MISSING_ISSUER_CERT);
+          goto leave;
+        }
+
+      ksba_cert_release (issuer_cert); issuer_cert = NULL;
+      rc = keydb_get_cert (kh, &issuer_cert);
+      if (rc)
+        {
+          log_error ("keydb_get_cert() failed: rc=%d\n", rc);
+          rc = gpg_error (GPG_ERR_GENERAL);
+          goto leave;
+        }
+
+    try_another_cert:
+      if (DBG_X509)
+        {
+          log_debug ("got issuer's certificate:\n");
+          gpgsm_dump_cert ("issuer", issuer_cert);
+        }
+
+      rc = gpgsm_check_cert_sig (issuer_cert, subject_cert);
+      if (rc)
+        {
+          do_list (0, listmode, listfp, _("certificate has a BAD signature"));
+          if (DBG_X509)
+            {
+              gpgsm_dump_cert ("signing issuer", issuer_cert);
+              gpgsm_dump_cert ("signed subject", subject_cert);
+            }
+          if (gpg_err_code (rc) == GPG_ERR_BAD_SIGNATURE)
+            {
+              /* We now try to find other issuer certificates which
+                 might have been used.  This is required because some
+                 CAs are reusing the issuer and subject DN for new
+                 root certificates. */
+              /* FIXME: Do this only if we don't have an
+                 AKI.keyIdentifier */
+              rc = find_up (ctrl, kh, subject_cert, issuer, 1);
+              if (!rc)
+                {
+                  ksba_cert_t tmp_cert;
+
+                  rc = keydb_get_cert (kh, &tmp_cert);
+                  if (rc || !compare_certs (issuer_cert, tmp_cert))
+                    {
+                      /* The find next did not work or returned an
+                         identical certificate.  We better stop here
+                         to avoid infinite checks. */
+                      /* No need to set RC because it is not used:
+                         rc = gpg_error (GPG_ERR_BAD_SIGNATURE);  */
+                      ksba_cert_release (tmp_cert);
+                    }
+                  else
+                    {
+                      do_list (0, listmode, listfp,
+                               _("found another possible matching "
+                                 "CA certificate - trying again"));
+                      ksba_cert_release (issuer_cert);
+                      issuer_cert = tmp_cert;
+                      goto try_another_cert;
+                    }
+                }
+            }
+
+          /* We give a more descriptive error code than the one
+             returned from the signature checking. */
+          rc = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+          goto leave;
+        }
+
+      is_root = gpgsm_is_root_cert (issuer_cert);
+      istrusted_rc = -1;
+
+
+      /* Check that a CA is allowed to issue certificates. */
+      {
+        int chainlen;
+
+        rc = allowed_ca (ctrl, issuer_cert, &chainlen, listmode, listfp);
+        if (rc)
+          {
+            /* Not allowed.  Check whether this is a trusted root
+               certificate and whether we allow special exceptions.
+               We could carry the result of the test over to the
+               regular root check at the top of the loop but for
+               clarity we won't do that.  Given that the majority of
+               certificates carry proper BasicContraints our way of
+               overriding an error in the way is justified for
+               performance reasons. */
+            if (is_root)
+              {
+                if (gpgsm_cert_has_well_known_private_key (issuer_cert))
+                  {
+                    memset (rootca_flags, 0, sizeof *rootca_flags);
+                    istrusted_rc = ((flags & VALIDATE_FLAG_STEED)
+                                    ? 0 : gpg_error (GPG_ERR_NOT_TRUSTED));
+                  }
+                else
+                  istrusted_rc = gpgsm_agent_istrusted
+                    (ctrl, issuer_cert, NULL, rootca_flags);
+
+                if (!istrusted_rc && rootca_flags->relax)
+                  {
+                    /* Ignore the error due to the relax flag.  */
+                    rc = 0;
+                    chainlen = -1;
+                  }
+              }
+          }
+        if (rc)
+          goto leave;
+        if (chainlen >= 0 && depth > chainlen)
+          {
+            do_list (1, listmode, listfp,
+                     _("certificate chain longer than allowed by CA (%d)"),
+                     chainlen);
+            rc = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+            goto leave;
+          }
+      }
+
+      /* Is the certificate allowed to sign other certificates. */
+      if (!listmode)
+        {
+          rc = gpgsm_cert_use_cert_p (issuer_cert);
+          if (rc)
+            {
+              char numbuf[50];
+              sprintf (numbuf, "%d", rc);
+              gpgsm_status2 (ctrl, STATUS_ERROR, "certcert.issuer.keyusage",
+                             numbuf, NULL);
+              goto leave;
+            }
+        }
+
+      /* Check for revocations etc.  Note that for a root certificate
+         this test is done a second time later. This should eventually
+         be fixed. */
+      if ((flags & VALIDATE_FLAG_NO_DIRMNGR))
+        rc = 0;
+      else if ((flags & VALIDATE_FLAG_STEED))
+        rc = 0; /* Fixme: XXX */
+      else if (is_root && (opt.no_trusted_cert_crl_check
+                           || (!istrusted_rc && rootca_flags->relax)))
+        rc = 0;
+      else
+        rc = is_cert_still_valid (ctrl,
+                                  (flags & VALIDATE_FLAG_CHAIN_MODEL),
+                                  listmode, listfp,
+                                  subject_cert, issuer_cert,
+                                  &any_revoked, &any_no_crl, &any_crl_too_old);
+      if (rc)
+        goto leave;
+
+
+      if (opt.verbose && !listmode)
+        log_info (depth == 0 ? _("certificate is good\n") :
+                  !is_root   ? _("intermediate certificate is good\n") :
+                  /* other */  _("root certificate is good\n"));
+
+      /* Under the chain model the next check time is the creation
+         time of the subject certificate.  */
+      if ( (flags & VALIDATE_FLAG_CHAIN_MODEL) )
+        {
+          rc = ksba_cert_get_validity (subject_cert, 0, check_time);
+          if (rc)
+            {
+              /* That will never happen as we have already checked
+                 this above.  */
+              BUG ();
+            }
+        }
+
+      /* For the next round the current issuer becomes the new subject.  */
+      keydb_search_reset (kh);
+      ksba_cert_release (subject_cert);
+      subject_cert = issuer_cert;
+      issuer_cert = NULL;
+      depth++;
+    } /* End chain traversal. */
+
+  if (!listmode && !opt.quiet)
+    {
+      if (opt.no_policy_check)
+        log_info ("policies not checked due to %s option\n",
+                  "--disable-policy-checks");
+      if (ctrl->offline || (opt.no_crl_check && !ctrl->use_ocsp))
+        log_info ("CRLs not checked due to %s option\n",
+                  ctrl->offline ? "offline" : "--disable-crl-checks");
+    }
+
+  if (!rc)
+    { /* If we encountered an error somewhere during the checks, set
+         the error code to the most critical one */
+      if (any_revoked)
+        rc = gpg_error (GPG_ERR_CERT_REVOKED);
+      else if (any_expired)
+        rc = gpg_error (GPG_ERR_CERT_EXPIRED);
+      else if (any_no_crl)
+        rc = gpg_error (GPG_ERR_NO_CRL_KNOWN);
+      else if (any_crl_too_old)
+        rc = gpg_error (GPG_ERR_CRL_TOO_OLD);
+      else if (any_no_policy_match)
+        rc = gpg_error (GPG_ERR_NO_POLICY_MATCH);
+    }
+
+ leave:
+  /* If we have traversed a complete chain up to the root we will
+     reset the ephemeral flag for all these certificates.  This is done
+     regardless of any error because those errors may only be
+     transient. */
+  if (chain && chain->is_root)
+    {
+      gpg_error_t err;
+      chain_item_t ci;
+
+      for (ci = chain; ci; ci = ci->next)
+        {
+          /* Note that it is possible for the last certificate in the
+             chain (i.e. our target certificate) that it has not yet
+             been stored in the keybox and thus the flag can't be set.
+             We ignore this error because it will later be stored
+             anyway.  */
+          err = keydb_set_cert_flags (ctrl, ci->cert, 1, KEYBOX_FLAG_BLOB, 0,
+                                      KEYBOX_FLAG_BLOB_EPHEMERAL, 0);
+          if (!ci->next && gpg_err_code (err) == GPG_ERR_NOT_FOUND)
+            ;
+          else if (err)
+            log_error ("clearing ephemeral flag failed: %s\n",
+                       gpg_strerror (err));
+        }
+    }
+
+  /* If we have figured something about the qualified signature
+     capability of the certificate under question, store the result as
+     user data in all certificates of the chain.  We do this even if the
+     validation itself failed.  */
+  if (is_qualified != -1 && !(flags & VALIDATE_FLAG_STEED))
+    {
+      gpg_error_t err;
+      chain_item_t ci;
+      char buf[1];
+
+      buf[0] = !!is_qualified;
+
+      for (ci = chain; ci; ci = ci->next)
+        {
+          err = ksba_cert_set_user_data (ci->cert, "is_qualified", buf, 1);
+          if (err)
+            {
+              log_error ("set_user_data(is_qualified) failed: %s\n",
+                         gpg_strerror (err));
+              if (!rc)
+                rc = err;
+            }
+        }
+    }
+
+  /* If auditing has been enabled, record what is in the chain.  */
+  if (ctrl->audit)
+    {
+      chain_item_t ci;
+
+      audit_log (ctrl->audit, AUDIT_CHAIN_BEGIN);
+      for (ci = chain; ci; ci = ci->next)
+        {
+          audit_log_cert (ctrl->audit,
+                          ci->is_root? AUDIT_CHAIN_ROOTCERT : AUDIT_CHAIN_CERT,
+                          ci->cert, 0);
+        }
+      audit_log (ctrl->audit, AUDIT_CHAIN_END);
+    }
+
+  if (r_exptime)
+    gnupg_copy_time (r_exptime, exptime);
+  xfree (issuer);
+  xfree (subject);
+  keydb_release (kh);
+  while (chain)
+    {
+      chain_item_t ci_next = chain->next;
+      ksba_cert_release (chain->cert);
+      xfree (chain);
+      chain = ci_next;
+    }
+  ksba_cert_release (issuer_cert);
+  ksba_cert_release (subject_cert);
+  return rc;
+}
+
+
+/* Validate a certificate chain.  For a description see
+   do_validate_chain.  This function is a wrapper to handle a root
+   certificate with the chain_model flag set.  If RETFLAGS is not
+   NULL, flags indicating now the verification was done are stored
+   there.  The only defined vits for RETFLAGS are
+   VALIDATE_FLAG_CHAIN_MODEL and VALIDATE_FLAG_STEED.
+
+   If you are verifying a signature you should set CHECKTIME to the
+   creation time of the signature.  If your are verifying a
+   certificate, set it nil (i.e. the empty string).  If the creation
+   date of the signature is not known use the special date
+   "19700101T000000" which is treated in a special way here. */
+int
+gpgsm_validate_chain (ctrl_t ctrl, ksba_cert_t cert, ksba_isotime_t checktime,
+                      ksba_isotime_t r_exptime,
+                      int listmode, estream_t listfp, unsigned int flags,
+                      unsigned int *retflags)
+{
+  int rc;
+  struct rootca_flags_s rootca_flags;
+  unsigned int dummy_retflags;
+
+  if (!retflags)
+    retflags = &dummy_retflags;
+
+  /* If the session requested a certain validation mode make sure the
+     corresponding flags are set.  */
+  if (ctrl->validation_model == 1)
+    flags |= VALIDATE_FLAG_CHAIN_MODEL;
+  else if (ctrl->validation_model == 2)
+    flags |= VALIDATE_FLAG_STEED;
+
+  /* If the chain model was forced, set this immediately into
+     RETFLAGS.  */
+  *retflags = (flags & VALIDATE_FLAG_CHAIN_MODEL);
+
+  memset (&rootca_flags, 0, sizeof rootca_flags);
+
+  rc = do_validate_chain (ctrl, cert, checktime,
+                          r_exptime, listmode, listfp, flags,
+                          &rootca_flags);
+  if (!rc && (flags & VALIDATE_FLAG_STEED))
+    {
+      *retflags |= VALIDATE_FLAG_STEED;
+    }
+  else if (gpg_err_code (rc) == GPG_ERR_CERT_EXPIRED
+      && !(flags & VALIDATE_FLAG_CHAIN_MODEL)
+      && (rootca_flags.valid && rootca_flags.chain_model))
+    {
+      do_list (0, listmode, listfp, _("switching to chain model"));
+      rc = do_validate_chain (ctrl, cert, checktime,
+                              r_exptime, listmode, listfp,
+                              (flags |= VALIDATE_FLAG_CHAIN_MODEL),
+                              &rootca_flags);
+      *retflags |= VALIDATE_FLAG_CHAIN_MODEL;
+    }
+
+  if (opt.verbose)
+    do_list (0, listmode, listfp, _("validation model used: %s"),
+             (*retflags & VALIDATE_FLAG_STEED)?
+             "steed" :
+             (*retflags & VALIDATE_FLAG_CHAIN_MODEL)?
+             _("chain"):_("shell"));
+
+  return rc;
+}
+
+
+/* Check that the given certificate is valid but DO NOT check any
+   constraints.  We assume that the issuers certificate is already in
+   the DB and that this one is valid; which it should be because it
+   has been checked using this function. */
+int
+gpgsm_basic_cert_check (ctrl_t ctrl, ksba_cert_t cert)
+{
+  int rc = 0;
+  char *issuer = NULL;
+  char *subject = NULL;
+  KEYDB_HANDLE kh;
+  ksba_cert_t issuer_cert = NULL;
+
+  if (opt.no_chain_validation)
+    {
+      log_info ("WARNING: bypassing basic certificate checks\n");
+      return 0;
+    }
+
+  kh = keydb_new ();
+  if (!kh)
+    {
+      log_error (_("failed to allocate keyDB handle\n"));
+      rc = gpg_error (GPG_ERR_GENERAL);
+      goto leave;
+    }
+
+  issuer = ksba_cert_get_issuer (cert, 0);
+  subject = ksba_cert_get_subject (cert, 0);
+  if (!issuer)
+    {
+      log_error ("no issuer found in certificate\n");
+      rc = gpg_error (GPG_ERR_BAD_CERT);
+      goto leave;
+    }
+
+  if (is_root_cert (cert, issuer, subject))
+    {
+      rc = gpgsm_check_cert_sig (cert, cert);
+      if (rc)
+        {
+          log_error ("self-signed certificate has a BAD signature: %s\n",
+                     gpg_strerror (rc));
+          if (DBG_X509)
+            {
+              gpgsm_dump_cert ("self-signing cert", cert);
+            }
+          rc = gpg_error (GPG_ERR_BAD_CERT);
+          goto leave;
+        }
+    }
+  else
+    {
+      /* Find the next cert up the tree. */
+      keydb_search_reset (kh);
+      rc = find_up (ctrl, kh, cert, issuer, 0);
+      if (rc)
+        {
+          if (rc == -1)
+            {
+              log_info ("issuer certificate (#/");
+              gpgsm_dump_string (issuer);
+              log_printf (") not found\n");
+            }
+          else
+            log_error ("failed to find issuer's certificate: rc=%d\n", rc);
+          rc = gpg_error (GPG_ERR_MISSING_ISSUER_CERT);
+          goto leave;
+        }
+
+      ksba_cert_release (issuer_cert); issuer_cert = NULL;
+      rc = keydb_get_cert (kh, &issuer_cert);
+      if (rc)
+        {
+          log_error ("keydb_get_cert() failed: rc=%d\n", rc);
+          rc = gpg_error (GPG_ERR_GENERAL);
+          goto leave;
+        }
+
+      rc = gpgsm_check_cert_sig (issuer_cert, cert);
+      if (rc)
+        {
+          log_error ("certificate has a BAD signature: %s\n",
+                     gpg_strerror (rc));
+          if (DBG_X509)
+            {
+              gpgsm_dump_cert ("signing issuer", issuer_cert);
+              gpgsm_dump_cert ("signed subject", cert);
+            }
+          rc = gpg_error (GPG_ERR_BAD_CERT);
+          goto leave;
+        }
+      if (opt.verbose)
+        log_info (_("certificate is good\n"));
+    }
+
+ leave:
+  xfree (issuer);
+  xfree (subject);
+  keydb_release (kh);
+  ksba_cert_release (issuer_cert);
+  return rc;
+}
+
+
+
+/* Check whether the certificate CERT has been issued by the German
+   authority for qualified signature.  They do not set the
+   basicConstraints and thus we need this workaround.  It works by
+   looking up the root certificate and checking whether that one is
+   listed as a qualified certificate for Germany.
+
+   We also try to cache this data but as long as don't keep a
+   reference to the certificate this won't be used.
+
+   Returns: True if CERT is a RegTP issued CA cert (i.e. the root
+   certificate itself or one of the CAs).  In that case CHAINLEN will
+   receive the length of the chain which is either 0 or 1.
+*/
+static int
+get_regtp_ca_info (ctrl_t ctrl, ksba_cert_t cert, int *chainlen)
+{
+  gpg_error_t err;
+  ksba_cert_t next;
+  int rc = 0;
+  int i, depth;
+  char country[3];
+  ksba_cert_t array[4];
+  char buf[2];
+  size_t buflen;
+  int dummy_chainlen;
+
+  if (!chainlen)
+    chainlen = &dummy_chainlen;
+
+  *chainlen = 0;
+  err = ksba_cert_get_user_data (cert, "regtp_ca_chainlen",
+                                 &buf, sizeof (buf), &buflen);
+  if (!err)
+    {
+      /* Got info. */
+      if (buflen < 2 || !*buf)
+        return 0; /* Nothing found. */
+      *chainlen = buf[1];
+      return 1; /* This is a regtp CA. */
+    }
+  else if (gpg_err_code (err) != GPG_ERR_NOT_FOUND)
+    {
+      log_error ("ksba_cert_get_user_data(%s) failed: %s\n",
+                 "regtp_ca_chainlen", gpg_strerror (err));
+      return 0; /* Nothing found.  */
+    }
+
+  /* Need to gather the info.  This requires to walk up the chain
+     until we have found the root.  Because we are only interested in
+     German Bundesnetzagentur (former RegTP) derived certificates 3
+     levels are enough.  (The German signature law demands a 3 tier
+     hierarchy; thus there is only one CA between the EE and the Root
+     CA.)  */
+  memset (&array, 0, sizeof array);
+
+  depth = 0;
+  ksba_cert_ref (cert);
+  array[depth++] = cert;
+  ksba_cert_ref (cert);
+  while (depth < DIM(array) && !(rc=gpgsm_walk_cert_chain (ctrl, cert, &next)))
+    {
+      ksba_cert_release (cert);
+      ksba_cert_ref (next);
+      array[depth++] = next;
+      cert = next;
+    }
+  ksba_cert_release (cert);
+  if (rc != -1 || !depth || depth == DIM(array) )
+    {
+      /* We did not reached the root. */
+      goto leave;
+    }
+
+  /* If this is a German signature law issued certificate, we store
+     additional information. */
+  if (!gpgsm_is_in_qualified_list (NULL, array[depth-1], country)
+      && !strcmp (country, "de"))
+    {
+      /* Setting the pathlen for the root CA and the CA flag for the
+         next one is all what we need to do. */
+      err = ksba_cert_set_user_data (array[depth-1], "regtp_ca_chainlen",
+                                     "\x01\x01", 2);
+      if (!err && depth > 1)
+        err = ksba_cert_set_user_data (array[depth-2], "regtp_ca_chainlen",
+                                       "\x01\x00", 2);
+      if (err)
+        log_error ("ksba_set_user_data(%s) failed: %s\n",
+                   "regtp_ca_chainlen", gpg_strerror (err));
+      for (i=0; i < depth; i++)
+        ksba_cert_release (array[i]);
+      *chainlen = (depth>1? 0:1);
+      return 1;
+    }
+
+ leave:
+  /* Nothing special with this certificate. Mark the target
+     certificate anyway to avoid duplicate lookups. */
+  err = ksba_cert_set_user_data (cert, "regtp_ca_chainlen", "", 1);
+  if (err)
+    log_error ("ksba_set_user_data(%s) failed: %s\n",
+               "regtp_ca_chainlen", gpg_strerror (err));
+  for (i=0; i < depth; i++)
+    ksba_cert_release (array[i]);
+  return 0;
+}