path: root/src/lib/x509/x509path.cpp

/*
* X.509 Certificate Path Validation
* (C) 2010,2011,2012,2014,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/x509path.h>
#include <botan/ocsp.h>
#include <botan/parsing.h>
#include <botan/pubkey.h>
#include <botan/oids.h>
#include <algorithm>
#include <chrono>
#include <vector>
#include <set>

#if defined(BOTAN_HAS_ONLINE_REVOCATION_CHECKS)
  #include <future>
  #include <botan/http_util.h>
#endif

namespace Botan {

/*
* PKIX path validation
*/
CertificatePathStatusCodes
PKIX::check_chain(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                  std::chrono::system_clock::time_point ref_time,
                  const std::string& hostname,
                  Usage_Type usage,
                  size_t min_signature_algo_strength,
                  const std::set<std::string>& trusted_hashes)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_chain cert_path empty");

   const bool self_signed_ee_cert = (cert_path.size() == 1);

   X509_Time validation_time(ref_time);

   CertificatePathStatusCodes cert_status(cert_path.size());

   if(!hostname.empty() && !cert_path[0]->matches_dns_name(hostname))
      cert_status[0].insert(Certificate_Status_Code::CERT_NAME_NOMATCH);

   if(!cert_path[0]->allowed_usage(usage))
      cert_status[0].insert(Certificate_Status_Code::INVALID_USAGE);

   for(size_t i = 0; i != cert_path.size(); ++i)
      {
      std::set<Certificate_Status_Code>& status = cert_status.at(i);

      const bool at_self_signed_root = (i == cert_path.size() - 1);

      const std::shared_ptr<const X509_Certificate>& subject = cert_path[i];

      const std::shared_ptr<const X509_Certificate>& issuer = cert_path[at_self_signed_root ? (i) : (i + 1)];

      if(at_self_signed_root && (issuer->is_self_signed() == false))
         {
         status.insert(Certificate_Status_Code::CHAIN_LACKS_TRUST_ROOT);
         }

      if(subject->issuer_dn() != issuer->subject_dn())
         {
         status.insert(Certificate_Status_Code::CHAIN_NAME_MISMATCH);
         }

      // Check all certs for valid time range
      if(validation_time < X509_Time(subject->start_time(), ASN1_Tag::UTC_OR_GENERALIZED_TIME))
         status.insert(Certificate_Status_Code::CERT_NOT_YET_VALID);

      if(validation_time > X509_Time(subject->end_time(), ASN1_Tag::UTC_OR_GENERALIZED_TIME))
         status.insert(Certificate_Status_Code::CERT_HAS_EXPIRED);

      // Check issuer constraints

      if(!issuer->is_CA_cert() && !self_signed_ee_cert)
         status.insert(Certificate_Status_Code::CA_CERT_NOT_FOR_CERT_ISSUER);

      if(issuer->path_limit() < i)
         status.insert(Certificate_Status_Code::CERT_CHAIN_TOO_LONG);

      std::unique_ptr<Public_Key> issuer_key(issuer->subject_public_key());

      if(!issuer_key)
         {
         status.insert(Certificate_Status_Code::CERT_PUBKEY_INVALID);
         }
      else
         {
         if(subject->check_signature(*issuer_key) == false)
            {
            status.insert(Certificate_Status_Code::SIGNATURE_ERROR);
            }

         if(issuer_key->estimated_strength() < min_signature_algo_strength)
            status.insert(Certificate_Status_Code::SIGNATURE_METHOD_TOO_WEAK);
         }

      // Ignore untrusted hashes on self-signed roots
      if(trusted_hashes.size() > 0 && !at_self_signed_root)
         {
         if(trusted_hashes.count(subject->hash_used_for_signature()) == 0)
            status.insert(Certificate_Status_Code::UNTRUSTED_HASH);
         }

      // Check cert extensions
      Extensions extensions = subject->v3_extensions();
      for(auto& extension : extensions.extensions())
         {
         extension.first->validate(*subject, *issuer, cert_path, cert_status, i);
         }
      }

   return cert_status;
   }

CertificatePathStatusCodes
PKIX::check_ocsp(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                 const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_responses,
                 const std::vector<Certificate_Store*>& trusted_certstores,
                 std::chrono::system_clock::time_point ref_time)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_ocsp cert_path empty");

   CertificatePathStatusCodes cert_status(cert_path.size() - 1);

   for(size_t i = 0; i != cert_path.size() - 1; ++i)
      {
      std::set<Certificate_Status_Code>& status = cert_status.at(i);

      std::shared_ptr<const X509_Certificate> subject = cert_path.at(i);
      std::shared_ptr<const X509_Certificate> ca = cert_path.at(i+1);

      if(i < ocsp_responses.size() && (ocsp_responses.at(i) != nullptr))
         {
         try
            {
            Certificate_Status_Code ocsp_signature_status = ocsp_responses.at(i)->check_signature(trusted_certstores, cert_path);

            if(ocsp_signature_status == Certificate_Status_Code::OCSP_SIGNATURE_OK)
               {
               // Signature ok, so check the claimed status
               Certificate_Status_Code ocsp_status = ocsp_responses.at(i)->status_for(*ca, *subject, ref_time);
               status.insert(ocsp_status);
               }
            else
               {
               // Some signature problem
               status.insert(ocsp_signature_status);
               }
            }
         catch(Exception& e)
            {
            status.insert(Certificate_Status_Code::OCSP_RESPONSE_INVALID);
            }
         }
      }

   while(cert_status.size() > 0 && cert_status.back().empty())
      cert_status.pop_back();

   return cert_status;
   }

CertificatePathStatusCodes
PKIX::check_crl(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                const std::vector<std::shared_ptr<const X509_CRL>>& crls,
                std::chrono::system_clock::time_point ref_time)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_crl cert_path empty");

   CertificatePathStatusCodes cert_status(cert_path.size());
   const X509_Time validation_time(ref_time);

   for(size_t i = 0; i != cert_path.size() - 1; ++i)
      {
      std::set<Certificate_Status_Code>& status = cert_status.at(i);

      if(i < crls.size() && crls.at(i))
         {
         std::shared_ptr<const X509_Certificate> subject = cert_path.at(i);
         std::shared_ptr<const X509_Certificate> ca = cert_path.at(i+1);

         if(!ca->allowed_usage(CRL_SIGN))
            status.insert(Certificate_Status_Code::CA_CERT_NOT_FOR_CRL_ISSUER);

         if(validation_time < X509_Time(crls[i]->this_update()))
            status.insert(Certificate_Status_Code::CRL_NOT_YET_VALID);

         if(validation_time > X509_Time(crls[i]->next_update()))
            status.insert(Certificate_Status_Code::CRL_HAS_EXPIRED);

         if(crls[i]->check_signature(ca->subject_public_key()) == false)
            status.insert(Certificate_Status_Code::CRL_BAD_SIGNATURE);

         status.insert(Certificate_Status_Code::VALID_CRL_CHECKED);

         if(crls[i]->is_revoked(*subject))
            status.insert(Certificate_Status_Code::CERT_IS_REVOKED);
         }
      }

   while(cert_status.size() > 0 && cert_status.back().empty())
      cert_status.pop_back();

   return cert_status;
   }

CertificatePathStatusCodes
PKIX::check_crl(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                const std::vector<Certificate_Store*>& certstores,
                std::chrono::system_clock::time_point ref_time)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_crl cert_path empty");

   if(certstores.empty())
      throw Invalid_Argument("PKIX::check_crl certstores empty");

   std::vector<std::shared_ptr<const X509_CRL>> crls(cert_path.size());

   for(size_t i = 0; i != cert_path.size(); ++i)
      {
      BOTAN_ASSERT_NONNULL(cert_path[i]);
      for(size_t c = 0; c != certstores.size(); ++c)
         {
         crls[i] = certstores[c]->find_crl_for(*cert_path[i]);
         if(crls[i])
            break;
         }
      }

   return PKIX::check_crl(cert_path, crls, ref_time);
   }

#if defined(BOTAN_HAS_ONLINE_REVOCATION_CHECKS)

CertificatePathStatusCodes
PKIX::check_ocsp_online(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                        const std::vector<Certificate_Store*>& trusted_certstores,
                        std::chrono::system_clock::time_point ref_time,
                        std::chrono::milliseconds timeout,
                        bool ocsp_check_intermediate_CAs)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_ocsp_online cert_path empty");

   std::vector<std::future<std::shared_ptr<const OCSP::Response>>> ocsp_response_futures;

   size_t to_ocsp = 1;

   if(ocsp_check_intermediate_CAs)
      to_ocsp = cert_path.size() - 1;
   if(cert_path.size() == 1)
      to_ocsp = 0;

   for(size_t i = 0; i < to_ocsp; ++i)
      {
      const std::shared_ptr<const X509_Certificate>& subject = cert_path.at(i);
      const std::shared_ptr<const X509_Certificate>& issuer = cert_path.at(i+1);

      if(subject->ocsp_responder() == "")
         {
         ocsp_response_futures.emplace_back(std::async(std::launch::deferred, [&]{
                  throw Exception("No OCSP responder URL set for this certificate");
                  return std::shared_ptr<const OCSP::Response>();
                  }));
            }
         else
            {
            ocsp_response_futures.emplace_back(std::async(std::launch::async, [&]{
                  OCSP::Request req(*issuer, *subject);

                  auto http = HTTP::POST_sync(subject->ocsp_responder(),
                                              "application/ocsp-request",
                                              req.BER_encode());

                  http.throw_unless_ok();
                  // Check the MIME type?

                  return std::make_shared<const OCSP::Response>(http.body());
                  }));
            }
      }

   std::vector<std::shared_ptr<const OCSP::Response>> ocsp_responses(ocsp_response_futures.size());

   for(size_t pass = 1; pass < 3; ++pass)
      {
      for(size_t i = 0; i < ocsp_response_futures.size(); ++i)
         {
         try
            {
            if(ocsp_responses[i] == nullptr && ocsp_response_futures[i].valid())
               {
               std::future_status status = ocsp_response_futures[i].wait_for(timeout);

               if(status == std::future_status::ready ||
                  status == std::future_status::deferred)
                  {
                  ocsp_responses[i] = ocsp_response_futures[i].get();
                  }
               }
            }
            catch(std::exception&)
               {
               // value is default initialized to null, no need to do anything
               }
         }
      }

   return PKIX::check_ocsp(cert_path, ocsp_responses, trusted_certstores, ref_time);
   }

CertificatePathStatusCodes
PKIX::check_crl_online(const std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                       const std::vector<Certificate_Store*>& certstores,
                       Certificate_Store_In_Memory* crl_store,
                       std::chrono::system_clock::time_point ref_time,
                       std::chrono::milliseconds timeout)
   {
   if(cert_path.empty())
      throw Invalid_Argument("PKIX::check_crl_online cert_path empty");
   if(certstores.empty())
      throw Invalid_Argument("PKIX::check_crl_online certstores empty");

   std::vector<std::future<std::shared_ptr<const X509_CRL>>> future_crls;
   std::vector<std::shared_ptr<const X509_CRL>> crls(cert_path.size());

   for(size_t i = 0; i != cert_path.size(); ++i)
      {
      for(size_t c = 0; c != certstores.size(); ++i)
         {
         crls[i] = certstores[i]->find_crl_for(*cert_path[i]);
         if(crls[i])
            break;
         }

      // TODO: check if CRL is expired and re-request?

      // Only request if we don't already have a CRL
      if(crls[i])
         {
         /*
         We already have a CRL, so just insert this empty one to hold a place in the vector
         so that indexes match up
         */
         future_crls.emplace_back(std::future<std::shared_ptr<const X509_CRL>>());
         }
      else if(cert_path[i]->crl_distribution_point() == "")
         {
         // Avoid creating a thread for this case
         future_crls.emplace_back(std::async(std::launch::deferred, [&]{
               throw Exception("No CRL distribution point for this certificate");
               return std::shared_ptr<const X509_CRL>();
               }));
         }
      else
         {
         future_crls.emplace_back(std::async(std::launch::async, [&]() {
               auto http = HTTP::GET_sync(cert_path[i]->crl_distribution_point());
               http.throw_unless_ok();
               // check the mime type?
               return std::make_shared<const X509_CRL>(http.body());
               }));
         }
      }

   for(size_t i = 0; i != future_crls.size(); ++i)
      {
      if(future_crls[i].valid())
         {
         try
            {
            std::future_status status = future_crls[i].wait_for(timeout);

            if(status == std::future_status::ready)
               {
               crls[i] = future_crls[i].get();
               }
            }
         catch(std::exception& e)
            {
            // crls[i] left null
            }
         }
      }

   const CertificatePathStatusCodes crl_status = PKIX::check_crl(cert_path, crls, ref_time);

   if(crl_store)
      {
      for(size_t i = 0; i != crl_status.size(); ++i)
         {
         if(crl_status[i].count(Certificate_Status_Code::VALID_CRL_CHECKED))
            {
            // better be non-null, we supposedly validated it
            BOTAN_ASSERT_NONNULL(crls[i]);
            crl_store->add_crl(crls[i]);
            }
         }
      }

   return crl_status;
   }

#endif

Certificate_Status_Code
PKIX::build_certificate_path(std::vector<std::shared_ptr<const X509_Certificate>>& cert_path,
                             const std::vector<Certificate_Store*>& trusted_certstores,
                             const std::shared_ptr<const X509_Certificate>& end_entity,
                             const std::vector<std::shared_ptr<const X509_Certificate>>& end_entity_extra)
   {
   if(end_entity->is_self_signed())
      {
      return Certificate_Status_Code::CANNOT_ESTABLISH_TRUST;
      }

   /*
   * This is an inelegant but functional way of preventing path loops
   * (where C1 -> C2 -> C3 -> C1). We store a set of all the certificate
   * fingerprints in the path. If there is a duplicate, we error out.
   * TODO: save fingerprints in result struct? Maybe useful for blacklists, etc.
   */
   std::set<std::string> certs_seen;

   cert_path.push_back(end_entity);
   certs_seen.insert(end_entity->fingerprint("SHA-256"));

   Certificate_Store_In_Memory ee_extras;
   for(size_t i = 0; i != end_entity_extra.size(); ++i)
      ee_extras.add_certificate(end_entity_extra[i]);

   // iterate until we reach a root or cannot find the issuer
   for(;;)
      {
      const X509_Certificate& last = *cert_path.back();
      const X509_DN issuer_dn = last.issuer_dn();
      const std::vector<uint8_t> auth_key_id = last.authority_key_id();

      std::shared_ptr<const X509_Certificate> issuer;
      bool trusted_issuer = false;

      for(Certificate_Store* store : trusted_certstores)
         {
         issuer = store->find_cert(issuer_dn, auth_key_id);
         if(issuer)
            {
            trusted_issuer = true;
            break;
            }
         }

      if(!issuer)
         {
         // fall back to searching supplemental certs
         issuer = ee_extras.find_cert(issuer_dn, auth_key_id);
         }

      if(!issuer)
         return Certificate_Status_Code::CERT_ISSUER_NOT_FOUND;

      const std::string fprint = issuer->fingerprint("SHA-256");

      if(certs_seen.count(fprint) > 0) // already seen?
         return Certificate_Status_Code::CERT_CHAIN_LOOP;

      certs_seen.insert(fprint);
      cert_path.push_back(issuer);

      if(issuer->is_self_signed())
         {
         if(trusted_issuer)
            {
            return Certificate_Status_Code::OK;
            }
         else
            {
            return Certificate_Status_Code::CANNOT_ESTABLISH_TRUST;
            }
         }
      }
   }

void PKIX::merge_revocation_status(CertificatePathStatusCodes& chain_status,
                                   const CertificatePathStatusCodes& crl,
                                   const CertificatePathStatusCodes& ocsp,
                                   bool require_rev_on_end_entity,
                                   bool require_rev_on_intermediates)
   {
   if(chain_status.empty())
      throw Invalid_Argument("PKIX::merge_revocation_status chain_status was empty");

   for(size_t i = 0; i != chain_status.size() - 1; ++i)
      {
      bool had_crl = false, had_ocsp = false;

      if(i < crl.size() && crl[i].size() > 0)
         {
         for(auto&& code : crl[i])
            {
            if(code == Certificate_Status_Code::VALID_CRL_CHECKED)
               {
               had_crl = true;
               }
            chain_status[i].insert(code);
            }
         }

      if(i < ocsp.size() && ocsp[i].size() > 0)
         {
         for(auto&& code : ocsp[i])
            {
            if(code == Certificate_Status_Code::OCSP_RESPONSE_GOOD)
               {
               had_ocsp = true;
               }

            chain_status[i].insert(code);
            }
         }

      if(had_crl == false && had_ocsp == false)
         {
         if((require_rev_on_end_entity && i == 0) ||
            (require_rev_on_intermediates && i > 0))
            {
            chain_status[i].insert(Certificate_Status_Code::NO_REVOCATION_DATA);
            }
         }
      }
   }

Certificate_Status_Code PKIX::overall_status(const CertificatePathStatusCodes& cert_status)
   {
   if(cert_status.empty())
      throw Invalid_Argument("PKIX::overall_status empty cert status");

   Certificate_Status_Code overall_status = Certificate_Status_Code::OK;

   // take the "worst" error as overall
   for(const std::set<Certificate_Status_Code>& s : cert_status)
      {
      if(!s.empty())
         {
         auto worst = *s.rbegin();
         // Leave informative OCSP/CRL confirmations on cert-level status only
         if(worst >= Certificate_Status_Code::FIRST_ERROR_STATUS && worst > overall_status)
            {
            overall_status = worst;
            }
         }
      }
   return overall_status;
   }

Path_Validation_Result x509_path_validate(
   const std::vector<X509_Certificate>& end_certs,
   const Path_Validation_Restrictions& restrictions,
   const std::vector<Certificate_Store*>& trusted_roots,
   const std::string& hostname,
   Usage_Type usage,
   std::chrono::system_clock::time_point ref_time,
   std::chrono::milliseconds ocsp_timeout,
   const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_resp)
   {
   if(end_certs.empty())
      throw Invalid_Argument("x509_path_validate called with no subjects");

   std::shared_ptr<const X509_Certificate> end_entity(std::make_shared<const X509_Certificate>(end_certs[0]));
   std::vector<std::shared_ptr<const X509_Certificate>> end_entity_extra;
   for(size_t i = 1; i < end_certs.size(); ++i)
      {
      end_entity_extra.push_back(std::make_shared<const X509_Certificate>(end_certs[i]));
      }

   std::vector<std::shared_ptr<const X509_Certificate>> cert_path;
   Certificate_Status_Code path_building_result =
      PKIX::build_certificate_path(cert_path, trusted_roots, end_entity, end_entity_extra);

   // If we cannot successfully build a chain to a trusted self-signed root, stop now
   if(path_building_result != Certificate_Status_Code::OK)
      {
      return Path_Validation_Result(path_building_result);
      }

   CertificatePathStatusCodes status =
      PKIX::check_chain(cert_path, ref_time,
                        hostname, usage,
                        restrictions.minimum_key_strength(),
                        restrictions.trusted_hashes());

   CertificatePathStatusCodes crl_status =
      PKIX::check_crl(cert_path, trusted_roots, ref_time);

   CertificatePathStatusCodes ocsp_status;

   if(ocsp_resp.size() > 0)
      {
      ocsp_status = PKIX::check_ocsp(cert_path, ocsp_resp, trusted_roots, ref_time);
      }

   if(ocsp_status.empty() && ocsp_timeout != std::chrono::milliseconds(0))
      {
#if defined(BOTAN_TARGET_OS_HAS_THREADS) && defined(BOTAN_HAS_HTTP_UTIL)
      ocsp_status = PKIX::check_ocsp_online(cert_path, trusted_roots, ref_time,
                                            ocsp_timeout, restrictions.ocsp_all_intermediates());
#else
      ocsp_status.resize(1);
      ocsp_status[0].insert(Certificate_Status_Code::OCSP_NO_HTTP);
#endif
      }

   PKIX::merge_revocation_status(status, crl_status, ocsp_status,
                                 restrictions.require_revocation_information(),
                                 restrictions.ocsp_all_intermediates());

   return Path_Validation_Result(status, std::move(cert_path));
   }

Path_Validation_Result x509_path_validate(
   const X509_Certificate& end_cert,
   const Path_Validation_Restrictions& restrictions,
   const std::vector<Certificate_Store*>& trusted_roots,
   const std::string& hostname,
   Usage_Type usage,
   std::chrono::system_clock::time_point when,
   std::chrono::milliseconds ocsp_timeout,
   const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_resp)
   {
   std::vector<X509_Certificate> certs;
   certs.push_back(end_cert);
   return x509_path_validate(certs, restrictions, trusted_roots, hostname, usage, when, ocsp_timeout, ocsp_resp);
   }

Path_Validation_Result x509_path_validate(
   const std::vector<X509_Certificate>& end_certs,
   const Path_Validation_Restrictions& restrictions,
   const Certificate_Store& store,
   const std::string& hostname,
   Usage_Type usage,
   std::chrono::system_clock::time_point when,
   std::chrono::milliseconds ocsp_timeout,
   const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_resp)
   {
   std::vector<Certificate_Store*> trusted_roots;
   trusted_roots.push_back(const_cast<Certificate_Store*>(&store));

   return x509_path_validate(end_certs, restrictions, trusted_roots, hostname, usage, when, ocsp_timeout, ocsp_resp);
   }

Path_Validation_Result x509_path_validate(
   const X509_Certificate& end_cert,
   const Path_Validation_Restrictions& restrictions,
   const Certificate_Store& store,
   const std::string& hostname,
   Usage_Type usage,
   std::chrono::system_clock::time_point when,
   std::chrono::milliseconds ocsp_timeout,
   const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_resp)
   {
   std::vector<X509_Certificate> certs;
   certs.push_back(end_cert);

   std::vector<Certificate_Store*> trusted_roots;
   trusted_roots.push_back(const_cast<Certificate_Store*>(&store));

   return x509_path_validate(certs, restrictions, trusted_roots, hostname, usage, when, ocsp_timeout, ocsp_resp);
   }

Path_Validation_Restrictions::Path_Validation_Restrictions(bool require_rev,
                                                           size_t key_strength,
                                                           bool ocsp_intermediates) :
   m_require_revocation_information(require_rev),
   m_ocsp_all_intermediates(ocsp_intermediates),
   m_minimum_key_strength(key_strength)
   {
   if(key_strength <= 80)
      m_trusted_hashes.insert("SHA-160");

   m_trusted_hashes.insert("SHA-224");
   m_trusted_hashes.insert("SHA-256");
   m_trusted_hashes.insert("SHA-384");
   m_trusted_hashes.insert("SHA-512");
   }

Path_Validation_Result::Path_Validation_Result(CertificatePathStatusCodes status,
                                               std::vector<std::shared_ptr<const X509_Certificate>>&& cert_chain) :
   m_all_status(status),
   m_cert_path(cert_chain),
   m_overall(PKIX::overall_status(m_all_status))
   {
   }

const X509_Certificate& Path_Validation_Result::trust_root() const
   {
   if(m_cert_path.empty())
      throw Exception("Path_Validation_Result::trust_root no path set");
   if(result() != Certificate_Status_Code::VERIFIED)
      throw Exception("Path_Validation_Result::trust_root meaningless with invalid status");

   return *m_cert_path[m_cert_path.size()-1];
   }

std::set<std::string> Path_Validation_Result::trusted_hashes() const
   {
   std::set<std::string> hashes;
   for(size_t i = 0; i != m_cert_path.size(); ++i)
      hashes.insert(m_cert_path[i]->hash_used_for_signature());
   return hashes;
   }

bool Path_Validation_Result::successful_validation() const
   {
   return (result() == Certificate_Status_Code::VERIFIED ||
           result() == Certificate_Status_Code::OCSP_RESPONSE_GOOD ||
           result() == Certificate_Status_Code::VALID_CRL_CHECKED);
   }

std::string Path_Validation_Result::result_string() const
   {
   return status_string(result());
   }

const char* Path_Validation_Result::status_string(Certificate_Status_Code code)
   {
   if(const char* s = to_string(code))
      return s;

   return "Unknown error";
   }

}