Adding upstream version 2.2.40.upstream/2.2.40

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

1 files changed, 1305 insertions, 0 deletions

diff --git a/dirmngr/validate.c b/dirmngr/validate.c
new file mode 100644
index 0000000..901c165
--- /dev/null
+++ b/dirmngr/validate.c
@@ -0,0 +1,1305 @@
+/* validate.c - Validate a certificate chain.
+ * Copyright (C) 2001, 2003, 2004, 2008 Free Software Foundation, Inc.
+ * Copyright (C) 2004, 2006, 2008, 2017 g10 Code GmbH
+ *
+ * This file is part of DirMngr.
+ *
+ * DirMngr 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.
+ *
+ * DirMngr 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <assert.h>
+#include <ctype.h>
+
+#include "dirmngr.h"
+#include "certcache.h"
+#include "crlcache.h"
+#include "validate.h"
+#include "misc.h"
+
+
+/* Mode parameters for cert_check_usage().  */
+enum cert_usage_modes
+  {
+    CERT_USAGE_MODE_SIGN,  /* Usable for encryption.            */
+    CERT_USAGE_MODE_ENCR,  /* Usable for signing.               */
+    CERT_USAGE_MODE_VRFY,  /* Usable for verification.          */
+    CERT_USAGE_MODE_DECR,  /* Usable for decryption.            */
+    CERT_USAGE_MODE_CERT,  /* Usable for cert signing.          */
+    CERT_USAGE_MODE_OCSP,  /* Usable for OCSP respone signing.  */
+    CERT_USAGE_MODE_CRL    /* Usable for CRL signing.           */
+  };
+
+
+/* While running the validation function we need to keep track of the
+   certificates and the validation outcome of each.  We use this type
+   for it.  */
+struct chain_item_s
+{
+  struct chain_item_s *next;
+  ksba_cert_t cert;      /* The certificate.  */
+  unsigned char fpr[20]; /* Fingerprint of the certificate.  */
+  int is_self_signed;    /* This certificate is self-signed.  */
+  int is_valid;          /* The certifiate is valid except for revocations.  */
+};
+typedef struct chain_item_s *chain_item_t;
+
+
+/* A couple of constants with Object Identifiers.  */
+static const char oid_kp_serverAuth[]     = "1.3.6.1.5.5.7.3.1";
+static const char oid_kp_clientAuth[]     = "1.3.6.1.5.5.7.3.2";
+static const char oid_kp_codeSigning[]    = "1.3.6.1.5.5.7.3.3";
+static const char oid_kp_emailProtection[]= "1.3.6.1.5.5.7.3.4";
+static const char oid_kp_timeStamping[]   = "1.3.6.1.5.5.7.3.8";
+static const char oid_kp_ocspSigning[]    = "1.3.6.1.5.5.7.3.9";
+
+
+/* Prototypes.  */
+static gpg_error_t check_cert_sig (ksba_cert_t issuer_cert, ksba_cert_t cert);
+
+
+/* Make sure that the values defined in the headers are correct.  We
+ * can't use the preprocessor due to the use of enums.  */
+static void
+check_header_constants (void)
+{
+  log_assert (CERTTRUST_CLASS_SYSTEM   == VALIDATE_FLAG_TRUST_SYSTEM);
+  log_assert (CERTTRUST_CLASS_CONFIG   == VALIDATE_FLAG_TRUST_CONFIG);
+  log_assert (CERTTRUST_CLASS_HKP      == VALIDATE_FLAG_TRUST_HKP);
+  log_assert (CERTTRUST_CLASS_HKPSPOOL == VALIDATE_FLAG_TRUST_HKPSPOOL);
+
+#undef  X
+#define X (VALIDATE_FLAG_TRUST_SYSTEM | VALIDATE_FLAG_TRUST_CONFIG  \
+           | VALIDATE_FLAG_TRUST_HKP | VALIDATE_FLAG_TRUST_HKPSPOOL)
+
+#if ( X & VALIDATE_FLAG_MASK_TRUST ) !=  X
+# error VALIDATE_FLAG_MASK_TRUST is bad
+#endif
+#if ( ~X & VALIDATE_FLAG_MASK_TRUST )
+# error VALIDATE_FLAG_MASK_TRUST is bad
+#endif
+
+#undef X
+}
+
+
+/* Check whether CERT contains critical extensions we don't know
+   about.  */
+static gpg_error_t
+unknown_criticals (ksba_cert_t cert)
+{
+  static const char *known[] = {
+    "2.5.29.15", /* keyUsage */
+    "2.5.29.19", /* basic Constraints */
+    "2.5.29.32", /* certificatePolicies */
+    "2.5.29.37", /* extendedKeyUsage */
+    NULL
+  };
+  int i, idx, crit;
+  const char *oid;
+  int unsupported;
+  strlist_t sl;
+  gpg_error_t err, rc;
+
+  rc = 0;
+  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)
+        {
+          log_error (_("critical certificate extension %s is not supported"),
+                     oid);
+          rc = gpg_error (GPG_ERR_UNSUPPORTED_CERT);
+        }
+    }
+  if (err && gpg_err_code (err) != GPG_ERR_EOF)
+    rc = err; /* Such an error takes precedence.  */
+
+  return rc;
+}
+
+
+/* Basic check for supported policies.  */
+static gpg_error_t
+check_cert_policy (ksba_cert_t cert)
+{
+  static const char *allowed[] = {
+    "2.289.9.9",
+    NULL
+  };
+  gpg_error_t err;
+  int idx;
+  char *p, *haystack;
+  char *policies;
+  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 certifiate 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)
+    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");
+
+  /* See whether we find ALLOWED (which is an OID) in POLICIES */
+  for (idx=0; allowed[idx]; idx++)
+    {
+      for (haystack=policies; (p=strstr (haystack, allowed[idx]));
+           haystack = p+1)
+        {
+          if ( !(p == policies || p[-1] == '\n') )
+            continue; /* Does not match the begin of a line. */
+          if (p[strlen (allowed[idx])] != ':')
+            continue; /* The length does not match. */
+          /* Yep - it does match: Return okay. */
+          ksba_free (policies);
+          return 0;
+        }
+    }
+
+  if (!any_critical)
+    {
+      log_info (_("Note: non-critical certificate policy not allowed"));
+      err = 0;
+    }
+  else
+    {
+      log_info (_("certificate policy not allowed"));
+      err = gpg_error (GPG_ERR_NO_POLICY_MATCH);
+    }
+
+  ksba_free (policies);
+  return err;
+}
+
+
+static gpg_error_t
+allowed_ca (ksba_cert_t cert, int *chainlen)
+{
+  gpg_error_t err;
+  int flag;
+
+  err = ksba_cert_is_ca (cert, &flag, chainlen);
+  if (err)
+    return err;
+  if (!flag)
+    {
+      if (!is_trusted_cert (cert, CERTTRUST_CLASS_CONFIG))
+        {
+          /* The German SigG Root CA's certificate does not flag
+             itself as a CA; thus we relax this requirement if we
+             trust a root CA.  I think this is reasonable.  Note, that
+             gpgsm implements a far stricter scheme here. */
+          if (chainlen)
+            *chainlen = 3; /* That is what the SigG implements. */
+          if (opt.verbose)
+            log_info (_("accepting root CA not marked as a CA"));
+        }
+      else
+        {
+          log_error (_("issuer certificate is not marked as a CA"));
+          return gpg_error (GPG_ERR_BAD_CA_CERT);
+        }
+    }
+  return 0;
+}
+
+/* Helper for validate_cert_chain.  */
+static gpg_error_t
+check_revocations (ctrl_t ctrl, chain_item_t chain)
+{
+  gpg_error_t err = 0;
+  int any_revoked = 0;
+  int any_no_crl = 0;
+  int any_crl_too_old = 0;
+  chain_item_t ci;
+
+  log_assert (ctrl->check_revocations_nest_level >= 0);
+  log_assert (chain);
+
+  if (ctrl->check_revocations_nest_level > 10)
+    {
+      log_error (_("CRL checking too deeply nested\n"));
+      return gpg_error(GPG_ERR_BAD_CERT_CHAIN);
+    }
+  ctrl->check_revocations_nest_level++;
+
+
+  for (ci=chain; ci; ci = ci->next)
+    {
+      assert (ci->cert);
+      if (ci == chain)
+        {
+          /* It does not make sense to check the root certificate for
+             revocations.  In almost all cases this will lead to a
+             catch-22 as the root certificate is the final trust
+             anchor for the certificates and the CRLs.  We expect the
+             user to remove root certificates from the list of trusted
+             certificates in case they have been revoked. */
+          if (opt.verbose)
+            cert_log_name (_("not checking CRL for"), ci->cert);
+          continue;
+        }
+
+      if (opt.verbose)
+        cert_log_name (_("checking CRL for"), ci->cert);
+      err = crl_cache_cert_isvalid (ctrl, ci->cert, 0);
+      if (gpg_err_code (err) == GPG_ERR_NO_CRL_KNOWN)
+        {
+          err = crl_cache_reload_crl (ctrl, ci->cert);
+          if (!err)
+            err = crl_cache_cert_isvalid (ctrl, ci->cert, 0);
+        }
+      switch (gpg_err_code (err))
+        {
+        case 0: err = 0; break;
+        case GPG_ERR_CERT_REVOKED: any_revoked = 1; err = 0; break;
+        case GPG_ERR_NO_CRL_KNOWN: any_no_crl = 1; err = 0; break;
+        case GPG_ERR_CRL_TOO_OLD: any_crl_too_old = 1; err = 0; break;
+        default: break;
+        }
+    }
+  ctrl->check_revocations_nest_level--;
+
+
+  if (err)
+    ;
+  else if (any_revoked)
+    err = gpg_error (GPG_ERR_CERT_REVOKED);
+  else if (any_no_crl)
+    err = gpg_error (GPG_ERR_NO_CRL_KNOWN);
+  else if (any_crl_too_old)
+    err = gpg_error (GPG_ERR_CRL_TOO_OLD);
+  else
+    err = 0;
+  return err;
+}
+
+
+/* Check whether CERT is a root certificate.  ISSUERDN and SUBJECTDN
+   are the DNs already extracted by the caller from CERT.  Returns
+   True if this is the case. */
+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 certificate (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;
+}
+
+
+/* Validate the certificate CHAIN up to the trust anchor. Optionally
+   return the closest expiration time in R_EXPTIME (this is useful for
+   caching issues).  MODE is one of the VALIDATE_MODE_* constants.
+
+   Note that VALIDATE_MODE_OCSP is not used due to the removal of the
+   system service in 2.1.15.  Instead only the callback to gpgsm to
+   validate a certificate is used.
+
+   If R_TRUST_ANCHOR is not NULL and the validation would fail only
+   because the root certificate is not trusted, the hexified
+   fingerprint of that root certificate is stored at R_TRUST_ANCHOR
+   and success is returned.  The caller needs to free the value at
+   R_TRUST_ANCHOR; in all other cases NULL is stored there.  */
+gpg_error_t
+validate_cert_chain (ctrl_t ctrl, ksba_cert_t cert, ksba_isotime_t r_exptime,
+                     unsigned int flags, char **r_trust_anchor)
+{
+  gpg_error_t err = 0;
+  int depth, maxdepth;
+  char *issuer = NULL;
+  char *subject = NULL;
+  ksba_cert_t subject_cert = NULL;
+  ksba_cert_t issuer_cert = NULL;
+  ksba_isotime_t current_time;
+  ksba_isotime_t exptime;
+  int any_expired = 0;
+  int any_no_policy_match = 0;
+  chain_item_t chain;
+
+  check_header_constants ();
+
+  if (r_exptime)
+    *r_exptime = 0;
+  *exptime = 0;
+
+  if (r_trust_anchor)
+    *r_trust_anchor = NULL;
+
+  if (DBG_X509)
+    dump_cert ("subject", cert);
+
+  /* May the target certificate be used for this purpose?  */
+  if ((flags & VALIDATE_FLAG_OCSP) && (err = check_cert_use_ocsp (cert)))
+    return err;
+  if ((flags & VALIDATE_FLAG_CRL) && (err = check_cert_use_crl (cert)))
+    return err;
+
+  /* If we already validated the certificate not too long ago, we can
+     avoid the excessive computations and lookups unless the caller
+     asked for the expiration time.  */
+  if (!r_exptime)
+    {
+      size_t buflen;
+      time_t validated_at;
+
+      err = ksba_cert_get_user_data (cert, "validated_at",
+                                     &validated_at, sizeof (validated_at),
+                                     &buflen);
+      if (err || buflen != sizeof (validated_at) || !validated_at)
+        err = 0; /* Not available or other error. */
+      else
+        {
+          /* If the validation is not older than 30 minutes we are ready. */
+          if (validated_at < gnupg_get_time () + (30*60))
+            {
+              if (opt.verbose)
+                log_info ("certificate is good (cached)\n");
+              /* Note, that we can't jump to leave here as this would
+                 falsely updated the validation timestamp.  */
+              return 0;
+            }
+        }
+    }
+
+  /* Get the current time. */
+  gnupg_get_isotime (current_time);
+
+  /* We walk up the chain until we find a trust anchor. */
+  subject_cert = cert;
+  maxdepth = 10;  /* Sensible limit on the length of the chain.  */
+  chain = NULL;
+  depth = 0;
+  for (;;)
+    {
+      /* Get the subject and issuer name from the current
+         certificate.  */
+      ksba_free (issuer);
+      ksba_free (subject);
+      issuer = ksba_cert_get_issuer (subject_cert, 0);
+      subject = ksba_cert_get_subject (subject_cert, 0);
+
+      if (!issuer)
+        {
+          log_error (_("no issuer found in certificate\n"));
+          err = gpg_error (GPG_ERR_BAD_CERT);
+          goto leave;
+        }
+
+      /* Handle the notBefore and notAfter timestamps.  */
+      {
+        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)
+          {
+            log_error (_("certificate with invalid validity: %s"),
+                       gpg_strerror (err));
+            err = gpg_error (GPG_ERR_BAD_CERT);
+            goto leave;
+          }
+
+        /* Keep track of the nearest expiration time in EXPTIME.  */
+        if (*not_after)
+          {
+            if (!*exptime)
+              gnupg_copy_time (exptime, not_after);
+            else if (strcmp (not_after, exptime) < 0 )
+              gnupg_copy_time (exptime, not_after);
+          }
+
+        /* Check whether the certificate is already valid.  */
+        if (*not_before && strcmp (current_time, not_before) < 0 )
+          {
+            log_error (_("certificate not yet valid"));
+            log_info ("(valid from ");
+            dump_isotime (not_before);
+            log_printf (")\n");
+            err = gpg_error (GPG_ERR_CERT_TOO_YOUNG);
+            goto leave;
+          }
+
+        /* Now check whether the certificate has expired.  */
+        if (*not_after && strcmp (current_time, not_after) > 0 )
+          {
+            log_error (_("certificate has expired"));
+            log_info ("(expired at ");
+            dump_isotime (not_after);
+            log_printf (")\n");
+            any_expired = 1;
+          }
+      }
+
+      /* Do we have any critical extensions in the certificate we
+         can't handle? */
+      err = unknown_criticals (subject_cert);
+      if (err)
+        goto leave; /* yes. */
+
+      /* Check that given policies are allowed.  */
+      err = check_cert_policy (subject_cert);
+      if (gpg_err_code (err) == GPG_ERR_NO_POLICY_MATCH)
+        {
+          any_no_policy_match = 1;
+          err = 0;
+        }
+      else if (err)
+        goto leave;
+
+      /* Is this a self-signed certificate? */
+      if (is_root_cert (subject_cert, issuer, subject))
+        {
+          /* Yes, this is our trust anchor.  */
+          if (check_cert_sig (subject_cert, subject_cert) )
+            {
+              log_error (_("selfsigned certificate has a BAD signature"));
+              err = gpg_error (depth? GPG_ERR_BAD_CERT_CHAIN
+                                    : GPG_ERR_BAD_CERT);
+              goto leave;
+            }
+
+          /* Is this certificate allowed to act as a CA.  */
+          err = allowed_ca (subject_cert, NULL);
+          if (err)
+            goto leave;  /* No. */
+
+          err = is_trusted_cert (subject_cert,
+                                 (flags & VALIDATE_FLAG_MASK_TRUST));
+          if (!err)
+            ; /* Yes we trust this cert.  */
+          else if (gpg_err_code (err) == GPG_ERR_NOT_TRUSTED)
+            {
+              char *fpr;
+
+              log_error (_("root certificate is not marked trusted"));
+              fpr = get_fingerprint_hexstring (subject_cert);
+              log_info (_("fingerprint=%s\n"), fpr? fpr : "?");
+              dump_cert ("issuer", subject_cert);
+              if (r_trust_anchor)
+                {
+                  /* Caller wants to do another trustiness check.  */
+                  *r_trust_anchor = fpr;
+                  err = 0;
+                }
+              else
+                xfree (fpr);
+            }
+          else
+            {
+              log_error (_("checking trustworthiness of "
+                           "root certificate failed: %s\n"),
+                         gpg_strerror (err));
+            }
+          if (err)
+            goto leave;
+
+          /* Prepend the certificate to our list.  */
+          {
+            chain_item_t ci;
+
+            ci = xtrycalloc (1, sizeof *ci);
+            if (!ci)
+              {
+                err = gpg_error_from_errno (errno);
+                goto leave;
+              }
+            ksba_cert_ref (subject_cert);
+            ci->cert = subject_cert;
+            cert_compute_fpr (subject_cert, ci->fpr);
+            ci->next = chain;
+            chain = ci;
+          }
+
+          if (opt.verbose)
+            {
+              if (r_trust_anchor && *r_trust_anchor)
+                log_info ("root certificate is good but not trusted\n");
+              else
+                log_info ("root certificate is good and trusted\n");
+            }
+
+          break;  /* Okay: a self-signed certificate is an end-point. */
+        }
+
+      /* To avoid loops, we use an arbitrary limit on the length of
+         the chain. */
+      depth++;
+      if (depth > maxdepth)
+        {
+          log_error (_("certificate chain too long\n"));
+          err = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+          goto leave;
+        }
+
+      /* Find the next cert up the tree. */
+      ksba_cert_release (issuer_cert); issuer_cert = NULL;
+      err = find_issuing_cert (ctrl, subject_cert, &issuer_cert);
+      if (err)
+        {
+          if (gpg_err_code (err) == GPG_ERR_NOT_FOUND)
+            {
+              log_error (_("issuer certificate not found"));
+              log_info ("issuer certificate: #/");
+              dump_string (issuer);
+              log_printf ("\n");
+            }
+          else
+            log_error (_("issuer certificate not found: %s\n"),
+                         gpg_strerror (err));
+          /* Use a better understandable error code.  */
+          err = gpg_error (GPG_ERR_MISSING_ISSUER_CERT);
+          goto leave;
+        }
+
+/*     try_another_cert: */
+      if (DBG_X509)
+        {
+          log_debug ("got issuer's certificate:\n");
+          dump_cert ("issuer", issuer_cert);
+        }
+
+      /* Now check the signature of the certificate.  FIXME: we should
+       * delay this until later so that faked certificates can't be
+       * turned into a DoS easily.  */
+      err = check_cert_sig (issuer_cert, subject_cert);
+      if (err)
+        {
+          log_error (_("certificate has a BAD signature"));
+#if 0
+          if (gpg_err_code (err) == 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 without using a  authorityKeyIdentifier. */
+              rc = find_up (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. */
+                      rc = gpg_error (GPG_ERR_BAD_SIGNATURE);
+                      ksba_cert_release (tmp_cert);
+                    }
+                  else
+                    {
+                      do_list (0, lm, fp, _("found another possible matching "
+                                            "CA certificate - trying again"));
+                      ksba_cert_release (issuer_cert);
+                      issuer_cert = tmp_cert;
+                      goto try_another_cert;
+                    }
+                }
+            }
+#endif
+          /* Return a more descriptive error code than the one
+           * returned from the signature checking.  */
+          err = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+          goto leave;
+        }
+
+      /* Check that the length of the chain is not longer than allowed
+       * by the CA.  */
+      {
+        int chainlen;
+
+        err = allowed_ca (issuer_cert, &chainlen);
+        if (err)
+          goto leave;
+        if (chainlen >= 0 && (depth - 1) > chainlen)
+          {
+            log_error (_("certificate chain longer than allowed by CA (%d)"),
+                       chainlen);
+            err = gpg_error (GPG_ERR_BAD_CERT_CHAIN);
+            goto leave;
+          }
+      }
+
+      /* May that certificate be used for certification? */
+      err = check_cert_use_cert (issuer_cert);
+      if (err)
+        goto leave;  /* No.  */
+
+      /* Prepend the certificate to our list.  */
+      {
+        chain_item_t ci;
+
+        ci = xtrycalloc (1, sizeof *ci);
+        if (!ci)
+          {
+            err = gpg_error_from_errno (errno);
+            goto leave;
+          }
+        ksba_cert_ref (subject_cert);
+        ci->cert = subject_cert;
+        cert_compute_fpr (subject_cert, ci->fpr);
+        ci->next = chain;
+        chain = ci;
+      }
+
+      if (opt.verbose)
+        log_info (_("certificate is good\n"));
+
+      /* Now to the next level up.  */
+      subject_cert = issuer_cert;
+      issuer_cert = NULL;
+    }
+
+  /* Even if we have no error here we need to check whether we
+   * encountered an error somewhere during the checks.  Set the error
+   * code to the most critical one.  */
+  if (!err)
+    {
+      if (any_expired)
+        err = gpg_error (GPG_ERR_CERT_EXPIRED);
+      else if (any_no_policy_match)
+        err = gpg_error (GPG_ERR_NO_POLICY_MATCH);
+    }
+
+  if (!err && opt.verbose)
+    {
+      chain_item_t citem;
+
+      log_info (_("certificate chain is good\n"));
+      for (citem = chain; citem; citem = citem->next)
+        cert_log_name ("  certificate", citem->cert);
+    }
+
+  /* Now check for revocations unless CRL checks are disabled or we
+   * are non-recursive CRL mode.  */
+  if (!err
+      && !(flags & VALIDATE_FLAG_NOCRLCHECK)
+      && !((flags & VALIDATE_FLAG_CRL)
+           && !(flags & VALIDATE_FLAG_RECURSIVE)))
+    { /* Now that everything is fine, walk the chain and check each
+       * certificate for revocations.
+       *
+       * 1. item in the chain  - The root certificate.
+       * 2. item               - the CA below the root
+       * last item             - the target certificate.
+       *
+       * Now for each certificate in the chain check whether it has
+       * been included in a CRL and thus be revoked.  We don't do OCSP
+       * here because this does not seem to make much sense.  This
+       * might become a recursive process and we should better cache
+       * our validity results to avoid double work.  Far worse a
+       * catch-22 may happen for an improper setup hierarchy and we
+       * need a way to break up such a deadlock.  */
+      err = check_revocations (ctrl, chain);
+    }
+
+  if (!err && opt.verbose)
+    {
+      if (r_trust_anchor && *r_trust_anchor)
+        log_info ("target certificate may be valid\n");
+      else
+        log_info ("target certificate is valid\n");
+    }
+  else if (err && opt.verbose)
+    log_info ("target certificate is NOT valid\n");
+
+
+ leave:
+  if (!err && !(r_trust_anchor && *r_trust_anchor))
+    {
+      /* With no error we can update the validation cache.  We do this
+       * for all certificates in the chain.  Note that we can't use
+       * the cache if the caller requested to check the trustiness of
+       * the root certificate himself.  Adding such a feature would
+       * require us to also store the fingerprint of root
+       * certificate.  */
+      chain_item_t citem;
+      time_t validated_at = gnupg_get_time ();
+
+      for (citem = chain; citem; citem = citem->next)
+        {
+          err = ksba_cert_set_user_data (citem->cert, "validated_at",
+                                         &validated_at, sizeof (validated_at));
+          if (err)
+            {
+              log_error ("set_user_data(validated_at) failed: %s\n",
+                         gpg_strerror (err));
+              err = 0;
+            }
+        }
+    }
+
+  if (r_exptime)
+    gnupg_copy_time (r_exptime, exptime);
+  ksba_free (issuer);
+  ksba_free (subject);
+  ksba_cert_release (issuer_cert);
+  if (subject_cert != cert)
+    ksba_cert_release (subject_cert);
+  while (chain)
+    {
+      chain_item_t ci_next = chain->next;
+      if (chain->cert)
+        ksba_cert_release (chain->cert);
+      xfree (chain);
+      chain = ci_next;
+    }
+  if (err && r_trust_anchor && *r_trust_anchor)
+    {
+      xfree (*r_trust_anchor);
+      *r_trust_anchor = NULL;
+    }
+  return err;
+}
+
+
+
+/* Return the public key algorithm id from the S-expression PKEY.
+   FIXME: libgcrypt should provide such a function.  Note that this
+   implementation uses the names as used by libksba.  */
+static int
+pk_algo_from_sexp (gcry_sexp_t pkey)
+{
+  gcry_sexp_t l1, l2;
+  const char *name;
+  size_t n;
+  int algo;
+
+  l1 = gcry_sexp_find_token (pkey, "public-key", 0);
+  if (!l1)
+    return 0; /* Not found.  */
+  l2 = gcry_sexp_cadr (l1);
+  gcry_sexp_release (l1);
+
+  name = gcry_sexp_nth_data (l2, 0, &n);
+  if (!name)
+    algo = 0; /* Not found. */
+  else if (n==3 && !memcmp (name, "rsa", 3))
+    algo = GCRY_PK_RSA;
+  else if (n==3 && !memcmp (name, "dsa", 3))
+    algo = GCRY_PK_DSA;
+  else if (n==13 && !memcmp (name, "ambiguous-rsa", 13))
+    algo = GCRY_PK_RSA;
+  else
+    algo = 0;
+  gcry_sexp_release (l2);
+  return algo;
+}
+
+
+/* Return the hash algorithm's algo id from its name given in the
+ * non-null termnated string in (buffer,buflen).  Returns 0 on failure
+ * or if the algo is not known.  */
+static int
+hash_algo_from_buffer (const void *buffer, size_t buflen)
+{
+  char *string;
+  int algo;
+
+  string = xtrymalloc (buflen + 1);
+  if (!string)
+    {
+      log_error (_("out of core\n"));
+      return 0;
+    }
+  memcpy (string, buffer, buflen);
+  string[buflen] = 0;
+  algo = gcry_md_map_name (string);
+  if (!algo)
+    log_error ("unknown digest algorithm '%s' used in certificate\n", string);
+  xfree (string);
+  return algo;
+}
+
+
+/* Return an unsigned integer from the non-null termnated string
+ * (buffer,buflen).  Returns 0 on failure.  */
+static unsigned int
+uint_from_buffer (const void *buffer, size_t buflen)
+{
+  char *string;
+  unsigned int val;
+
+  string = xtrymalloc (buflen + 1);
+  if (!string)
+    {
+      log_error (_("out of core\n"));
+      return 0;
+    }
+  memcpy (string, buffer, buflen);
+  string[buflen] = 0;
+  val = strtoul (string, NULL, 10);
+  xfree (string);
+  return val;
+}
+
+
+/* Check the signature on CERT using the ISSUER_CERT.  This function
+ * does only test the cryptographic signature and nothing else.  It is
+ * assumed that the ISSUER_CERT is valid.  */
+static gpg_error_t
+check_cert_sig (ksba_cert_t issuer_cert, ksba_cert_t cert)
+{
+  gpg_error_t err;
+  const char *algoid;
+  gcry_md_hd_t md;
+  int algo;
+  ksba_sexp_t p;
+  size_t n;
+  gcry_sexp_t s_sig, s_hash, s_pkey;
+  const char *algo_name; /* hash algorithm name converted to lower case. */
+  int digestlen;
+  unsigned char *digest;
+  int use_pss = 0;
+  unsigned int saltlen;
+
+  /* Hash the target certificate using the algorithm from that certificate.  */
+  algoid = ksba_cert_get_digest_algo (cert);
+  algo = gcry_md_map_name (algoid);
+  if (!algo && algoid && !strcmp (algoid, "1.2.840.113549.1.1.10"))
+    use_pss = 1;
+  else if (!algo)
+    {
+      log_error (_("unknown hash algorithm '%s'\n"), algoid? algoid:"?");
+      return gpg_error (GPG_ERR_GENERAL);
+    }
+
+  /* Get the signature value out of the target certificate.  */
+  p = ksba_cert_get_sig_val (cert);
+  n = gcry_sexp_canon_len (p, 0, NULL, NULL);
+  if (!n)
+    {
+      log_error ("libksba did not return a proper S-Exp\n");
+      ksba_free (p);
+      return gpg_error (GPG_ERR_BUG);
+    }
+  err = gcry_sexp_sscan ( &s_sig, NULL, p, n);
+  ksba_free (p);
+  if (err)
+    {
+      log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (err));
+      return err;
+    }
+  if (DBG_CRYPTO)
+    gcry_log_debugsxp ("sigval", s_sig);
+
+  if (use_pss)
+    {
+      /* Extract the hash algorithm and the salt length from the sigval.  */
+      gcry_buffer_t ioarray[2] = { {0}, {0} };
+
+      err = gcry_sexp_extract_param (s_sig, "sig-val",
+                                    "&'hash-algo''salt-length'",
+                                    ioarray+0, ioarray+1, NULL);
+      if (err)
+        {
+          gcry_sexp_release (s_sig);
+          log_error ("extracting params from PSS failed: %s\n",
+                     gpg_strerror (err));
+          return err;
+        }
+      algo = hash_algo_from_buffer (ioarray[0].data, ioarray[0].len);
+      saltlen = uint_from_buffer (ioarray[1].data, ioarray[1].len);
+      xfree (ioarray[0].data);
+      xfree (ioarray[1].data);
+      if (saltlen < 20)
+        {
+          log_error ("length of PSS salt too short\n");
+          gcry_sexp_release (s_sig);
+          return gpg_error (GPG_ERR_DIGEST_ALGO);
+        }
+      if (!algo)
+        {
+          gcry_sexp_release (s_sig);
+          return gpg_error (GPG_ERR_DIGEST_ALGO);
+        }
+      /* Add some restrictions; see ../sm/certcheck.c for details.  */
+      switch (algo)
+        {
+        case GCRY_MD_SHA1:
+        case GCRY_MD_SHA256:
+        case GCRY_MD_SHA384:
+        case GCRY_MD_SHA512:
+        case GCRY_MD_SHA3_256:
+        case GCRY_MD_SHA3_384:
+        case GCRY_MD_SHA3_512:
+          break;
+        default:
+          log_error ("PSS hash algorithm '%s' rejected\n",
+                     gcry_md_algo_name (algo));
+          gcry_sexp_release (s_sig);
+          return gpg_error (GPG_ERR_DIGEST_ALGO);
+        }
+
+      if (gcry_md_get_algo_dlen (algo) != saltlen)
+        {
+          log_error ("PSS hash algorithm '%s' rejected due to salt length %u\n",
+                     gcry_md_algo_name (algo), saltlen);
+          gcry_sexp_release (s_sig);
+          return gpg_error (GPG_ERR_DIGEST_ALGO);
+        }
+    }
+
+  algo_name = hash_algo_to_string (algo);
+  err = gcry_md_open (&md, algo, 0);
+  if (err)
+    {
+      log_error ("md_open failed: %s\n", gpg_strerror (err));
+      gcry_sexp_release (s_sig);
+      return err;
+    }
+  if (DBG_HASHING)
+    gcry_md_debug (md, "hash.cert");
+
+  err = ksba_cert_hash (cert, 1, HASH_FNC, md);
+  if (err)
+    {
+      log_error ("ksba_cert_hash failed: %s\n", gpg_strerror (err));
+      gcry_md_close (md);
+      gcry_sexp_release (s_sig);
+      return err;
+    }
+  gcry_md_final (md);
+
+  /* Get the public key from the issuer certificate.  */
+  p = ksba_cert_get_public_key (issuer_cert);
+  n = gcry_sexp_canon_len (p, 0, NULL, NULL);
+  if (!n)
+    {
+      log_error ("libksba did not return a proper S-Exp\n");
+      gcry_md_close (md);
+      ksba_free (p);
+      gcry_sexp_release (s_sig);
+      return gpg_error (GPG_ERR_BUG);
+    }
+  err = gcry_sexp_sscan ( &s_pkey, NULL, p, n);
+  ksba_free (p);
+  if (err)
+    {
+      log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (err));
+      gcry_md_close (md);
+      gcry_sexp_release (s_sig);
+      return err;
+    }
+
+
+  /* Prepare the values for signature verification. At this point we
+   * have these values:
+   *
+   * S_PKEY    - S-expression with the issuer's public key.
+   * S_SIG     - Signature value as given in the certificate.
+   * MD        - Finalized hash context with hash of the certificate.
+   * ALGO_NAME - Lowercase hash algorithm name
+   * SALTLEN   - Salt length for rsaPSS.
+   */
+  digestlen = gcry_md_get_algo_dlen (algo);
+  digest = gcry_md_read (md, algo);
+  if (use_pss)
+    {
+      err = gcry_sexp_build (&s_hash, NULL,
+                             "(data (flags pss)"
+                             "(hash %s %b)"
+                             "(salt-length %u))",
+                             algo_name,
+                             (int)digestlen,
+                             digest,
+                             saltlen);
+    }
+  else if (pk_algo_from_sexp (s_pkey) == GCRY_PK_DSA)
+    {
+      /* NB.: We support only SHA-1 here because we had problems back
+       * then to get test data for DSA-2.  Meanwhile DSA has been
+       * replaced by ECDSA which we do not yet support.  */
+      if (digestlen != 20)
+        {
+          log_error ("DSA requires the use of a 160 bit hash algorithm\n");
+          gcry_md_close (md);
+          gcry_sexp_release (s_sig);
+          gcry_sexp_release (s_pkey);
+          return gpg_error (GPG_ERR_INTERNAL);
+        }
+      err = gcry_sexp_build (&s_hash, NULL, "(data(flags raw)(value %b))",
+                             (int)digestlen, digest);
+    }
+  else /* Not DSA - we assume RSA  */
+    {
+      err = gcry_sexp_build (&s_hash, NULL, "(data(flags pkcs1)(hash %s %b))",
+                             algo_name, (int)digestlen, digest);
+    }
+
+  if (!err)
+    err = gcry_pk_verify (s_sig, s_hash, s_pkey);
+  if (DBG_X509)
+    log_debug ("gcry_pk_verify: %s\n", gpg_strerror (err));
+  gcry_md_close (md);
+  gcry_sexp_release (s_sig);
+  gcry_sexp_release (s_hash);
+  gcry_sexp_release (s_pkey);
+  return err;
+}
+
+
+
+/* Return 0 if CERT is usable for MODE.  */
+static gpg_error_t
+check_cert_usage (ksba_cert_t cert, enum cert_usage_modes mode)
+{
+  gpg_error_t err;
+  unsigned int use;
+  char *extkeyusages;
+  int have_ocsp_signing = 0;
+
+  err = ksba_cert_get_ext_key_usages (cert, &extkeyusages);
+  if (gpg_err_code (err) == GPG_ERR_NO_DATA)
+    err = 0; /* No policy given. */
+  if (!err)
+    {
+      unsigned int extusemask = ~0; /* Allow all. */
+
+      if (extkeyusages)
+        {
+          char *p, *pend;
+          int any_critical = 0;
+
+          extusemask = 0;
+
+          p = extkeyusages;
+          while (p && (pend=strchr (p, ':')))
+            {
+              *pend++ = 0;
+              /* Only care about critical flagged usages. */
+              if ( *pend == 'C' )
+                {
+                  any_critical = 1;
+                  if ( !strcmp (p, oid_kp_serverAuth))
+                    extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE
+                                   | KSBA_KEYUSAGE_KEY_ENCIPHERMENT
+                                   | KSBA_KEYUSAGE_KEY_AGREEMENT);
+                  else if ( !strcmp (p, oid_kp_clientAuth))
+                    extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE
+                                   | KSBA_KEYUSAGE_KEY_AGREEMENT);
+                  else if ( !strcmp (p, oid_kp_codeSigning))
+                    extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE);
+                  else if ( !strcmp (p, oid_kp_emailProtection))
+                    extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE
+                                   | KSBA_KEYUSAGE_NON_REPUDIATION
+                                   | KSBA_KEYUSAGE_KEY_ENCIPHERMENT
+                                   | KSBA_KEYUSAGE_KEY_AGREEMENT);
+                  else if ( !strcmp (p, oid_kp_timeStamping))
+                    extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE
+                                   | KSBA_KEYUSAGE_NON_REPUDIATION);
+                }
+
+              /* This is a hack to cope with OCSP.  Note that we do
+                 not yet fully comply with the requirements and that
+                 the entire CRL/OCSP checking thing should undergo a
+                 thorough review and probably redesign. */
+              if ( !strcmp (p, oid_kp_ocspSigning))
+                have_ocsp_signing = 1;
+
+              if ((p = strchr (pend, '\n')))
+                p++;
+            }
+          ksba_free (extkeyusages);
+          extkeyusages = NULL;
+
+          if (!any_critical)
+            extusemask = ~0; /* Reset to the don't care mask. */
+        }
+
+
+      err = ksba_cert_get_key_usage (cert, &use);
+      if (gpg_err_code (err) == GPG_ERR_NO_DATA)
+        {
+          err = 0;
+          if (opt.verbose && (mode == CERT_USAGE_MODE_SIGN
+                              || mode == CERT_USAGE_MODE_ENCR))
+            log_info (_("no key usage specified - assuming all usages\n"));
+          use = ~0;
+        }
+
+      /* Apply extKeyUsage. */
+      use &= extusemask;
+
+    }
+  if (err)
+    {
+      log_error (_("error getting key usage information: %s\n"),
+                 gpg_strerror (err));
+      ksba_free (extkeyusages);
+      return err;
+    }
+
+  switch (mode)
+    {
+    case CERT_USAGE_MODE_SIGN:
+    case CERT_USAGE_MODE_VRFY:
+      if ((use & (KSBA_KEYUSAGE_DIGITAL_SIGNATURE
+                  | KSBA_KEYUSAGE_NON_REPUDIATION)))
+        return 0;
+      log_info (mode == CERT_USAGE_MODE_VRFY
+                ? _("certificate should not have been used for signing\n")
+                : _("certificate is not usable for signing\n"));
+      break;
+
+    case CERT_USAGE_MODE_ENCR:
+    case CERT_USAGE_MODE_DECR:
+      if ((use & (KSBA_KEYUSAGE_KEY_ENCIPHERMENT
+                  | KSBA_KEYUSAGE_DATA_ENCIPHERMENT)))
+        return 0;
+      log_info (mode == CERT_USAGE_MODE_DECR
+                ? _("certificate should not have been used for encryption\n")
+                : _("certificate is not usable for encryption\n"));
+      break;
+
+    case CERT_USAGE_MODE_CERT:
+      if ((use & (KSBA_KEYUSAGE_KEY_CERT_SIGN)))
+        return 0;
+      log_info (_("certificate should not have "
+                  "been used for certification\n"));
+      break;
+
+    case CERT_USAGE_MODE_OCSP:
+      if (use != ~0
+          && (have_ocsp_signing
+              || (use & (KSBA_KEYUSAGE_KEY_CERT_SIGN
+                         |KSBA_KEYUSAGE_CRL_SIGN))))
+        return 0;
+      log_info (_("certificate should not have "
+                  "been used for OCSP response signing\n"));
+      break;
+
+    case CERT_USAGE_MODE_CRL:
+      if ((use & (KSBA_KEYUSAGE_CRL_SIGN)))
+        return 0;
+      log_info (_("certificate should not have "
+                  "been used for CRL signing\n"));
+      break;
+    }
+
+  return gpg_error (GPG_ERR_WRONG_KEY_USAGE);
+}
+
+
+/* Return 0 if the certificate CERT is usable for certification.  */
+gpg_error_t
+check_cert_use_cert (ksba_cert_t cert)
+{
+  return check_cert_usage (cert, CERT_USAGE_MODE_CERT);
+}
+
+/* Return 0 if the certificate CERT is usable for signing OCSP
+   responses.  */
+gpg_error_t
+check_cert_use_ocsp (ksba_cert_t cert)
+{
+  return check_cert_usage (cert, CERT_USAGE_MODE_OCSP);
+}
+
+/* Return 0 if the certificate CERT is usable for signing CRLs. */
+gpg_error_t
+check_cert_use_crl (ksba_cert_t cert)
+{
+  return check_cert_usage (cert, CERT_USAGE_MODE_CRL);
+}