x509cert.cpp

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/*
* X.509 Certificates
* (C) 1999-2010,2015,2017 Jack Lloyd
* (C) 2016 René Korthaus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/x509cert.h>
 
#include <botan/ber_dec.h>
#include <botan/bigint.h>
#include <botan/hash.h>
#include <botan/hex.h>
#include <botan/pk_keys.h>
#include <botan/x509_ext.h>
#include <botan/x509_key.h>
#include <botan/internal/parsing.h>
#include <algorithm>
#include <sstream>
 
namespace Botan {
 
struct X509_Certificate_Data {
      std::vector<uint8_t> m_serial;
      AlgorithmIdentifier m_sig_algo_inner;
      X509_DN m_issuer_dn;
      X509_DN m_subject_dn;
      std::vector<uint8_t> m_issuer_dn_bits;
      std::vector<uint8_t> m_subject_dn_bits;
      X509_Time m_not_before;
      X509_Time m_not_after;
      std::vector<uint8_t> m_subject_public_key_bits;
      std::vector<uint8_t> m_subject_public_key_bits_seq;
      std::vector<uint8_t> m_subject_public_key_bitstring;
      std::vector<uint8_t> m_subject_public_key_bitstring_sha1;
      AlgorithmIdentifier m_subject_public_key_algid;
 
      std::vector<uint8_t> m_v2_issuer_key_id;
      std::vector<uint8_t> m_v2_subject_key_id;
      Extensions m_v3_extensions;
 
      std::vector<OID> m_extended_key_usage;
      std::vector<uint8_t> m_authority_key_id;
      std::vector<uint8_t> m_subject_key_id;
      std::vector<OID> m_cert_policies;
 
      std::vector<std::string> m_crl_distribution_points;
      std::string m_ocsp_responder;
      std::vector<std::string> m_ca_issuers;
 
      std::vector<uint8_t> m_issuer_dn_bits_sha256;
      std::vector<uint8_t> m_subject_dn_bits_sha256;
 
      std::string m_fingerprint_sha1;
      std::string m_fingerprint_sha256;
 
      AlternativeName m_subject_alt_name;
      AlternativeName m_issuer_alt_name;
      NameConstraints m_name_constraints;
 
      size_t m_version = 0;
      std::optional<size_t> m_path_len_constraint;
      Key_Constraints m_key_constraints;
      bool m_self_signed = false;
      bool m_is_ca_certificate = false;
      bool m_serial_negative = false;
      bool m_subject_alt_name_exists = false;
};
 
X509_Certificate::~X509_Certificate() = default;
 
std::string X509_Certificate::PEM_label() const {
   return "CERTIFICATE";
}
 
std::vector<std::string> X509_Certificate::alternate_PEM_labels() const {
   return {"X509 CERTIFICATE"};
}
 
X509_Certificate::X509_Certificate(DataSource& src) {
   load_data(src);
}
 
X509_Certificate::X509_Certificate(const std::vector<uint8_t>& vec) {
   DataSource_Memory src(vec.data(), vec.size());
   load_data(src);
}
 
X509_Certificate::X509_Certificate(const uint8_t data[], size_t len) {
   DataSource_Memory src(data, len);
   load_data(src);
}
 
#if defined(BOTAN_TARGET_OS_HAS_FILESYSTEM)
X509_Certificate::X509_Certificate(std::string_view fsname) {
   DataSource_Stream src(fsname, true);
   load_data(src);
}
#endif
 
namespace {
 
std::unique_ptr<X509_Certificate_Data> parse_x509_cert_body(const X509_Object& obj) {
   auto data = std::make_unique<X509_Certificate_Data>();
 
   BigInt serial_bn;
   BER_Object public_key;
   BER_Object v3_exts_data;
 
   BER_Decoder(obj.signed_body())
      .decode_optional(data->m_version, ASN1_Type(0), ASN1_Class::Constructed | ASN1_Class::ContextSpecific)
      .decode(serial_bn)
      .decode(data->m_sig_algo_inner)
      .decode(data->m_issuer_dn)
      .start_sequence()
      .decode(data->m_not_before)
      .decode(data->m_not_after)
      .end_cons()
      .decode(data->m_subject_dn)
      .get_next(public_key)
      .decode_optional_string(data->m_v2_issuer_key_id, ASN1_Type::BitString, 1)
      .decode_optional_string(data->m_v2_subject_key_id, ASN1_Type::BitString, 2)
      .get_next(v3_exts_data)
      .verify_end("TBSCertificate has extra data after extensions block");
 
   if(data->m_version > 2) {
      throw Decoding_Error("Unknown X.509 cert version " + std::to_string(data->m_version));
   }
   if(obj.signature_algorithm() != data->m_sig_algo_inner) {
      throw Decoding_Error("X.509 Certificate had differing algorithm identifers in inner and outer ID fields");
   }
 
   public_key.assert_is_a(ASN1_Type::Sequence, ASN1_Class::Constructed, "X.509 certificate public key");
 
   // for general sanity convert wire version (0 based) to standards version (v1 .. v3)
   data->m_version += 1;
 
   data->m_serial = serial_bn.serialize();
   // crude method to save the serial's sign; will get lost during decoding, otherwise
   data->m_serial_negative = serial_bn.is_negative();
   data->m_subject_dn_bits = ASN1::put_in_sequence(data->m_subject_dn.get_bits());
   data->m_issuer_dn_bits = ASN1::put_in_sequence(data->m_issuer_dn.get_bits());
 
   data->m_subject_public_key_bits.assign(public_key.bits(), public_key.bits() + public_key.length());
 
   data->m_subject_public_key_bits_seq = ASN1::put_in_sequence(data->m_subject_public_key_bits);
 
   BER_Decoder(data->m_subject_public_key_bits)
      .decode(data->m_subject_public_key_algid)
      .decode(data->m_subject_public_key_bitstring, ASN1_Type::BitString);
 
   if(v3_exts_data.is_a(3, ASN1_Class::Constructed | ASN1_Class::ContextSpecific)) {
      // Path validation will reject a v1/v2 cert with v3 extensions
      BER_Decoder(v3_exts_data).decode(data->m_v3_extensions).verify_end();
   } else if(v3_exts_data.is_set()) {
      throw BER_Bad_Tag("Unknown tag in X.509 cert", v3_exts_data.tagging());
   }
 
   // Now cache some fields from the extensions
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Key_Usage>()) {
      data->m_key_constraints = ext->get_constraints();
      /*
      RFC 5280: When the keyUsage extension appears in a certificate,
      at least one of the bits MUST be set to 1.
      */
      if(data->m_key_constraints.empty()) {
         throw Decoding_Error("Certificate has invalid encoding for KeyUsage");
      }
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Subject_Key_ID>()) {
      data->m_subject_key_id = ext->get_key_id();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Authority_Key_ID>()) {
      data->m_authority_key_id = ext->get_key_id();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Name_Constraints>()) {
      data->m_name_constraints = ext->get_name_constraints();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Extended_Key_Usage>()) {
      data->m_extended_key_usage = ext->object_identifiers();
      /*
      RFC 5280 section 4.2.1.12
 
      "This extension indicates one or more purposes ..."
 
      "If the extension is present, then the certificate MUST only be
      used for one of the purposes indicated."
 
      Thus we reject an EKU extension which is empty, since this indicates
      the certificate cannot be used for any purpose.
      */
      if(data->m_extended_key_usage.empty()) {
         throw Decoding_Error("Certificate has invalid empty EKU extension");
      }
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Basic_Constraints>()) {
      if(ext->is_ca() == true) {
         /*
         * RFC 5280 section 4.2.1.3 requires that CAs include KeyUsage in all
         * intermediate CA certificates they issue. Currently we accept it being
         * missing, as do most other implementations. But it may be worth
         * removing this entirely, or alternately adding a warning level
         * validation failure for it.
         */
         const bool allowed_by_ku =
            data->m_key_constraints.includes(Key_Constraints::KeyCertSign) || data->m_key_constraints.empty();
 
         /*
         * If the extended key usages are set then we must restrict the
         * usage in accordance with it as well.
         *
         * RFC 5280 does not define any extended key usages compatible
         * with certificate signing, but some CAs seem to use serverAuth
         * or clientAuth here.
         */
         const bool allowed_by_ext_ku = [](const std::vector<OID>& ext_ku) -> bool {
            if(ext_ku.empty()) {
               return true;
            }
 
            const auto server_auth = OID::from_name("PKIX.ServerAuth");
            const auto client_auth = OID::from_name("PKIX.ClientAuth");
            const auto ocsp_sign = OID::from_name("PKIX.OCSPSigning");
 
            for(const auto& oid : ext_ku) {
               if(oid == server_auth || oid == client_auth || oid == ocsp_sign) {
                  return true;
               }
            }
 
            return false;
         }(data->m_extended_key_usage);
 
         if(allowed_by_ku && allowed_by_ext_ku) {
            data->m_is_ca_certificate = true;
            data->m_path_len_constraint = ext->path_length_constraint();
         }
      }
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Issuer_Alternative_Name>()) {
      data->m_issuer_alt_name = ext->get_alt_name();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Subject_Alternative_Name>()) {
      data->m_subject_alt_name = ext->get_alt_name();
   }
 
   // This will be set even if SAN parsing failed entirely eg due to a decoding error
   // or if the SAN is empty. This is used to guard against using the CN for domain
   // name checking.
   const auto san_oid = OID::from_string("X509v3.SubjectAlternativeName");
   data->m_subject_alt_name_exists = data->m_v3_extensions.extension_set(san_oid);
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Certificate_Policies>()) {
      data->m_cert_policies = ext->get_policy_oids();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::Authority_Information_Access>()) {
      data->m_ocsp_responder = ext->ocsp_responder();
      data->m_ca_issuers = ext->ca_issuers();
   }
 
   if(const auto* ext = data->m_v3_extensions.get_extension_object_as<Cert_Extension::CRL_Distribution_Points>()) {
      data->m_crl_distribution_points = ext->crl_distribution_urls();
   }
 
   // Check for self-signed vs self-issued certificates
   if(data->m_subject_dn == data->m_issuer_dn) {
      if(data->m_subject_key_id.empty() == false && data->m_authority_key_id.empty() == false) {
         data->m_self_signed = (data->m_subject_key_id == data->m_authority_key_id);
      } else {
         /*
         If a parse error or unknown algorithm is encountered, default
         to assuming it is self signed. We have no way of being certain but
         that is usually the default case (self-issued is rare in practice).
         */
         data->m_self_signed = true;
 
         try {
            auto pub_key = X509::load_key(data->m_subject_public_key_bits_seq);
 
            const auto sig_status = obj.verify_signature(*pub_key);
 
            if(sig_status.first == Certificate_Status_Code::OK ||
               sig_status.first == Certificate_Status_Code::SIGNATURE_ALGO_UNKNOWN) {
               data->m_self_signed = true;
            } else {
               data->m_self_signed = false;
            }
         } catch(...) {
            // ignore errors here to allow parsing to continue
         }
      }
   }
 
   const std::vector<uint8_t> full_encoding = obj.BER_encode();
 
   if(auto sha1 = HashFunction::create("SHA-1")) {
      sha1->update(data->m_subject_public_key_bitstring);
      data->m_subject_public_key_bitstring_sha1 = sha1->final_stdvec();
      // otherwise left as empty, and we will throw if subject_public_key_bitstring_sha1 is called
 
      data->m_fingerprint_sha1 = create_hex_fingerprint(full_encoding, "SHA-1");
   }
 
   if(auto sha256 = HashFunction::create("SHA-256")) {
      sha256->update(data->m_issuer_dn_bits);
      data->m_issuer_dn_bits_sha256 = sha256->final_stdvec();
 
      sha256->update(data->m_subject_dn_bits);
      data->m_subject_dn_bits_sha256 = sha256->final_stdvec();
 
      data->m_fingerprint_sha256 = create_hex_fingerprint(full_encoding, "SHA-256");
   }
 
   return data;
}
 
}  // namespace
 
/*
* Decode the TBSCertificate data
*/
void X509_Certificate::force_decode() {
   m_data.reset();
   m_data = parse_x509_cert_body(*this);
}
 
const X509_Certificate_Data& X509_Certificate::data() const {
   if(m_data == nullptr) {
      throw Invalid_State("X509_Certificate uninitialized");
   }
   return *m_data;
}
 
uint32_t X509_Certificate::x509_version() const {
   return static_cast<uint32_t>(data().m_version);
}
 
bool X509_Certificate::is_self_signed() const {
   return data().m_self_signed;
}
 
const X509_Time& X509_Certificate::not_before() const {
   return data().m_not_before;
}
 
const X509_Time& X509_Certificate::not_after() const {
   return data().m_not_after;
}
 
const AlgorithmIdentifier& X509_Certificate::subject_public_key_algo() const {
   return data().m_subject_public_key_algid;
}
 
const std::vector<uint8_t>& X509_Certificate::v2_issuer_key_id() const {
   return data().m_v2_issuer_key_id;
}
 
const std::vector<uint8_t>& X509_Certificate::v2_subject_key_id() const {
   return data().m_v2_subject_key_id;
}
 
const std::vector<uint8_t>& X509_Certificate::subject_public_key_bits() const {
   return data().m_subject_public_key_bits;
}
 
const std::vector<uint8_t>& X509_Certificate::subject_public_key_info() const {
   return data().m_subject_public_key_bits_seq;
}
 
const std::vector<uint8_t>& X509_Certificate::subject_public_key_bitstring() const {
   return data().m_subject_public_key_bitstring;
}
 
const std::vector<uint8_t>& X509_Certificate::subject_public_key_bitstring_sha1() const {
   if(data().m_subject_public_key_bitstring_sha1.empty()) {
      throw Encoding_Error("X509_Certificate::subject_public_key_bitstring_sha1 called but SHA-1 disabled in build");
   }
 
   return data().m_subject_public_key_bitstring_sha1;
}
 
const std::vector<uint8_t>& X509_Certificate::authority_key_id() const {
   return data().m_authority_key_id;
}
 
const std::vector<uint8_t>& X509_Certificate::subject_key_id() const {
   return data().m_subject_key_id;
}
 
const std::vector<uint8_t>& X509_Certificate::serial_number() const {
   return data().m_serial;
}
 
bool X509_Certificate::is_serial_negative() const {
   return data().m_serial_negative;
}
 
const X509_DN& X509_Certificate::issuer_dn() const {
   return data().m_issuer_dn;
}
 
const X509_DN& X509_Certificate::subject_dn() const {
   return data().m_subject_dn;
}
 
const std::vector<uint8_t>& X509_Certificate::raw_issuer_dn() const {
   return data().m_issuer_dn_bits;
}
 
const std::vector<uint8_t>& X509_Certificate::raw_subject_dn() const {
   return data().m_subject_dn_bits;
}
 
bool X509_Certificate::is_CA_cert() const {
   if(data().m_version < 3 && data().m_self_signed) {
      return true;
   }
 
   return data().m_is_ca_certificate;
}
 
uint32_t X509_Certificate::path_limit() const {
   if(data().m_version < 3 && data().m_self_signed) {
      return 32;  // in theory infinite, but this is more than enough
   }
 
   return static_cast<uint32_t>(data().m_path_len_constraint.value_or(Cert_Extension::NO_CERT_PATH_LIMIT));
}
 
std::optional<size_t> X509_Certificate::path_length_constraint() const {
   return data().m_path_len_constraint;
}
 
Key_Constraints X509_Certificate::constraints() const {
   return data().m_key_constraints;
}
 
const std::vector<OID>& X509_Certificate::extended_key_usage() const {
   return data().m_extended_key_usage;
}
 
const std::vector<OID>& X509_Certificate::certificate_policy_oids() const {
   return data().m_cert_policies;
}
 
const NameConstraints& X509_Certificate::name_constraints() const {
   return data().m_name_constraints;
}
 
const Extensions& X509_Certificate::v3_extensions() const {
   return data().m_v3_extensions;
}
 
bool X509_Certificate::has_constraints(Key_Constraints usage) const {
   // Unlike allowed_usage, returns false if constraints was not set
   return constraints().includes(usage);
}
 
bool X509_Certificate::allowed_usage(Key_Constraints usage) const {
   if(constraints().empty()) {
      return true;
   }
   return constraints().includes(usage);
}
 
bool X509_Certificate::allowed_extended_usage(std::string_view usage) const {
   return allowed_extended_usage(OID::from_string(usage));
}
 
bool X509_Certificate::allowed_extended_usage(const OID& usage) const {
   const std::vector<OID>& ex = extended_key_usage();
   if(ex.empty()) {
      return true;
   }
 
   if(std::find(ex.begin(), ex.end(), usage) != ex.end()) {
      return true;
   }
 
   return false;
}
 
bool X509_Certificate::allowed_usage(Usage_Type usage) const {
   // These follow suggestions in RFC 5280 4.2.1.12
 
   switch(usage) {
      case Usage_Type::UNSPECIFIED:
         return true;
 
      case Usage_Type::TLS_SERVER_AUTH:
         return (allowed_usage(Key_Constraints::KeyAgreement) || allowed_usage(Key_Constraints::KeyEncipherment) ||
                 allowed_usage(Key_Constraints::DigitalSignature)) &&
                allowed_extended_usage("PKIX.ServerAuth");
 
      case Usage_Type::TLS_CLIENT_AUTH:
         return (allowed_usage(Key_Constraints::DigitalSignature) || allowed_usage(Key_Constraints::KeyAgreement)) &&
                allowed_extended_usage("PKIX.ClientAuth");
 
      case Usage_Type::OCSP_RESPONDER:
         return (allowed_usage(Key_Constraints::DigitalSignature) || allowed_usage(Key_Constraints::NonRepudiation)) &&
                has_ex_constraint("PKIX.OCSPSigning");
 
      case Usage_Type::CERTIFICATE_AUTHORITY:
         return is_CA_cert();
 
      case Usage_Type::ENCRYPTION:
         return (allowed_usage(Key_Constraints::KeyEncipherment) || allowed_usage(Key_Constraints::DataEncipherment));
   }
 
   return false;
}
 
bool X509_Certificate::has_ex_constraint(std::string_view ex_constraint) const {
   return has_ex_constraint(OID::from_string(ex_constraint));
}
 
bool X509_Certificate::has_ex_constraint(const OID& usage) const {
   const std::vector<OID>& ex = extended_key_usage();
   return (std::find(ex.begin(), ex.end(), usage) != ex.end());
}
 
/*
* Return if a certificate extension is marked critical
*/
bool X509_Certificate::is_critical(std::string_view ex_name) const {
   return v3_extensions().critical_extension_set(OID::from_string(ex_name));
}
 
std::string X509_Certificate::ocsp_responder() const {
   return data().m_ocsp_responder;
}
 
std::vector<std::string> X509_Certificate::ca_issuers() const {
   return data().m_ca_issuers;
}
 
std::vector<std::string> X509_Certificate::crl_distribution_points() const {
   return data().m_crl_distribution_points;
}
 
std::string X509_Certificate::crl_distribution_point() const {
   // just returns the first (arbitrarily)
   if(!data().m_crl_distribution_points.empty()) {
      return data().m_crl_distribution_points[0];
   }
   return "";
}
 
const AlternativeName& X509_Certificate::subject_alt_name() const {
   return data().m_subject_alt_name;
}
 
const AlternativeName& X509_Certificate::issuer_alt_name() const {
   return data().m_issuer_alt_name;
}
 
namespace {
 
std::vector<std::string> get_cert_user_info(std::string_view req, const X509_DN& dn, const AlternativeName& alt_name) {
   auto set_to_vector = [](const std::set<std::string>& s) -> std::vector<std::string> { return {s.begin(), s.end()}; };
 
   if(dn.has_field(req)) {
      return dn.get_attribute(req);
   } else if(req == "RFC822" || req == "Email") {
      return set_to_vector(alt_name.email());
   } else if(req == "DNS") {
      return set_to_vector(alt_name.dns());
   } else if(req == "URI") {
      return set_to_vector(alt_name.uris());
   } else if(req == "IP") {
      std::vector<std::string> ip_str;
      for(uint32_t ipv4 : alt_name.ipv4_address()) {
         ip_str.push_back(ipv4_to_string(ipv4));
      }
      return ip_str;
   } else {
      return {};
   }
}
 
}  // namespace
 
/*
* Return information about the subject
*/
std::vector<std::string> X509_Certificate::subject_info(std::string_view req) const {
   return get_cert_user_info(req, subject_dn(), subject_alt_name());
}
 
/*
* Return information about the issuer
*/
std::vector<std::string> X509_Certificate::issuer_info(std::string_view req) const {
   return get_cert_user_info(req, issuer_dn(), issuer_alt_name());
}
 
/*
* Return the public key in this certificate
*/
std::unique_ptr<Public_Key> X509_Certificate::subject_public_key() const {
   try {
      return std::unique_ptr<Public_Key>(X509::load_key(subject_public_key_info()));
   } catch(std::exception& e) {
      throw Decoding_Error("X509_Certificate::subject_public_key", e);
   }
}
 
std::unique_ptr<Public_Key> X509_Certificate::load_subject_public_key() const {
   return this->subject_public_key();
}
 
std::vector<uint8_t> X509_Certificate::raw_issuer_dn_sha256() const {
   if(data().m_issuer_dn_bits_sha256.empty()) {
      throw Encoding_Error("X509_Certificate::raw_issuer_dn_sha256 called but SHA-256 disabled in build");
   }
   return data().m_issuer_dn_bits_sha256;
}
 
std::vector<uint8_t> X509_Certificate::raw_subject_dn_sha256() const {
   if(data().m_subject_dn_bits_sha256.empty()) {
      throw Encoding_Error("X509_Certificate::raw_subject_dn_sha256 called but SHA-256 disabled in build");
   }
   return data().m_subject_dn_bits_sha256;
}
 
std::string X509_Certificate::fingerprint(std::string_view hash_name) const {
   /*
   * The SHA-1 and SHA-256 fingerprints are precomputed since these
   * are the most commonly used. Especially, SHA-256 fingerprints are
   * used for cycle detection during path construction.
   *
   * If SHA-1 or SHA-256 was missing at parsing time the vectors are
   * left empty in which case we fall back to create_hex_fingerprint
   * which will throw if the hash is unavailable.
   */
   if(hash_name == "SHA-256" && !data().m_fingerprint_sha256.empty()) {
      return data().m_fingerprint_sha256;
   } else if(hash_name == "SHA-1" && !data().m_fingerprint_sha1.empty()) {
      return data().m_fingerprint_sha1;
   } else {
      return create_hex_fingerprint(this->BER_encode(), hash_name);
   }
}
 
bool X509_Certificate::matches_dns_name(std::string_view name) const {
   if(name.empty()) {
      return false;
   }
 
   if(auto req_ipv4 = string_to_ipv4(name)) {
      const auto& ipv4_names = subject_alt_name().ipv4_address();
      return ipv4_names.contains(req_ipv4.value());
   } else {
      auto issued_names = subject_info("DNS");
 
      // Fall back to CN only if no SAN is included
      if(!data().m_subject_alt_name_exists) {
         issued_names = subject_info("Name");
      }
 
      for(const auto& issued_name : issued_names) {
         if(host_wildcard_match(issued_name, name)) {
            return true;
         }
      }
   }
 
   return false;
}
 
/*
* Compare two certificates for equality
*/
bool X509_Certificate::operator==(const X509_Certificate& other) const {
   return (this->signature() == other.signature() && this->signature_algorithm() == other.signature_algorithm() &&
           this->signed_body() == other.signed_body());
}
 
bool X509_Certificate::operator<(const X509_Certificate& other) const {
   /* If signature values are not equal, sort by lexicographic ordering of that */
   if(this->signature() != other.signature()) {
      return (this->signature() < other.signature());
   }
 
   // Then compare the signed contents
   return this->signed_body() < other.signed_body();
}
 
/*
* X.509 Certificate Comparison
*/
bool operator!=(const X509_Certificate& cert1, const X509_Certificate& cert2) {
   return !(cert1 == cert2);
}
 
std::string X509_Certificate::to_string() const {
   std::ostringstream out;
 
   out << "Version: " << this->x509_version() << "\n";
   out << "Subject: " << subject_dn() << "\n";
   out << "Issuer: " << issuer_dn() << "\n";
   out << "Issued: " << this->not_before().readable_string() << "\n";
   out << "Expires: " << this->not_after().readable_string() << "\n";
 
   try {
      auto pubkey = this->subject_public_key();
      out << "Public Key [" << pubkey->algo_name() << "-" << pubkey->key_length() << "]\n\n";
      out << X509::PEM_encode(*pubkey) << "\n";
   } catch(const Decoding_Error& ex) {
      const AlgorithmIdentifier& alg_id = this->subject_public_key_algo();
      out << "Public Key Invalid!\n"
          << " OID: " << alg_id.oid().to_formatted_string() << "\n"
          << " Error: " << ex.what() << "\n"
          << " Hex: " << hex_encode(this->subject_public_key_bitstring()) << "\n";
   }
 
   out << "Constraints:\n";
   Key_Constraints constraints = this->constraints();
   if(constraints.empty()) {
      out << " No key constraints set\n";
   } else {
      if(constraints.includes(Key_Constraints::DigitalSignature)) {
         out << "   Digital Signature\n";
      }
      if(constraints.includes(Key_Constraints::NonRepudiation)) {
         out << "   Non-Repudiation\n";
      }
      if(constraints.includes(Key_Constraints::KeyEncipherment)) {
         out << "   Key Encipherment\n";
      }
      if(constraints.includes(Key_Constraints::DataEncipherment)) {
         out << "   Data Encipherment\n";
      }
      if(constraints.includes(Key_Constraints::KeyAgreement)) {
         out << "   Key Agreement\n";
      }
      if(constraints.includes(Key_Constraints::KeyCertSign)) {
         out << "   Cert Sign\n";
      }
      if(constraints.includes(Key_Constraints::CrlSign)) {
         out << "   CRL Sign\n";
      }
      if(constraints.includes(Key_Constraints::EncipherOnly)) {
         out << "   Encipher Only\n";
      }
      if(constraints.includes(Key_Constraints::DecipherOnly)) {
         out << "   Decipher Only\n";
      }
   }
 
   const std::vector<OID>& policies = this->certificate_policy_oids();
   if(!policies.empty()) {
      out << "Policies: "
          << "\n";
      for(const auto& oid : policies) {
         out << "   " << oid.to_string() << "\n";
      }
   }
 
   const std::vector<OID>& ex_constraints = this->extended_key_usage();
   if(!ex_constraints.empty()) {
      out << "Extended Constraints:\n";
      for(auto&& oid : ex_constraints) {
         out << "   " << oid.to_formatted_string() << "\n";
      }
   }
 
   const NameConstraints& name_constraints = this->name_constraints();
 
   if(!name_constraints.permitted().empty() || !name_constraints.excluded().empty()) {
      out << "Name Constraints:\n";
 
      if(!name_constraints.permitted().empty()) {
         out << "   Permit";
         for(const auto& st : name_constraints.permitted()) {
            out << " " << st.base();
         }
         out << "\n";
      }
 
      if(!name_constraints.excluded().empty()) {
         out << "   Exclude";
         for(const auto& st : name_constraints.excluded()) {
            out << " " << st.base();
         }
         out << "\n";
      }
   }
 
   if(!ocsp_responder().empty()) {
      out << "OCSP responder " << ocsp_responder() << "\n";
   }
 
   const std::vector<std::string> ca_issuers = this->ca_issuers();
   if(!ca_issuers.empty()) {
      out << "CA Issuers:\n";
      for(const auto& ca_issuer : ca_issuers) {
         out << "   URI: " << ca_issuer << "\n";
      }
   }
 
   for(const auto& cdp : crl_distribution_points()) {
      out << "CRL " << cdp << "\n";
   }
 
   out << "Signature algorithm: " << this->signature_algorithm().oid().to_formatted_string() << "\n";
 
   out << "Serial number: " << hex_encode(this->serial_number()) << "\n";
 
   if(!this->authority_key_id().empty()) {
      out << "Authority keyid: " << hex_encode(this->authority_key_id()) << "\n";
   }
 
   if(!this->subject_key_id().empty()) {
      out << "Subject keyid: " << hex_encode(this->subject_key_id()) << "\n";
   }
 
   if(this->is_self_signed()) {
      out << "Certificate is self signed\n";
   }
 
   return out.str();
}
 
}  // namespace Botan