msg_cert_verify_13.cpp

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/*
* Certificate Verify Message
* (C) 2021-2022 Jack Lloyd
*     2021 Elektrobit Automotive GmbH
*     2022 René Meusel, Hannes Rantzsch - neXenio GmbH
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/tls_messages_13.h>
 
#include <botan/credentials_manager.h>
#include <botan/pk_keys.h>
#include <botan/tls_callbacks.h>
#include <botan/tls_exceptn.h>
#include <botan/tls_policy.h>
#include <botan/internal/stl_util.h>
 
namespace Botan::TLS {
 
namespace {
 
std::vector<uint8_t> message(Connection_Side side, const Transcript_Hash& hash) {
   std::vector<uint8_t> msg(64, 0x20);
   msg.reserve(64 + 33 + 1 + hash.size());
 
   const std::string context_string = (side == TLS::Connection_Side::Server) ? "TLS 1.3, server CertificateVerify"
                                                                             : "TLS 1.3, client CertificateVerify";
 
   msg.insert(msg.end(), context_string.cbegin(), context_string.cend());
   msg.push_back(0x00);
 
   msg.insert(msg.end(), hash.cbegin(), hash.cend());
   return msg;
}
 
Signature_Scheme choose_signature_scheme(const Private_Key& key,
                                         const std::vector<Signature_Scheme>& allowed_schemes,
                                         const std::vector<Signature_Scheme>& peer_allowed_schemes) {
   for(Signature_Scheme scheme : allowed_schemes) {
      // RFC 8446 4.4.3 forbids the rsa_pkcs1_* schemes in CertificateVerify, those are TLS 1.2 only.
      if(scheme.is_available() && scheme.is_compatible_with(Protocol_Version::TLS_V13) && scheme.is_suitable_for(key) &&
         value_exists(peer_allowed_schemes, scheme)) {
         return scheme;
      }
   }
 
   throw TLS_Exception(Alert::HandshakeFailure, "Failed to agree on a signature algorithm");
}
 
}  // namespace
 
/*
* Create a new Certificate Verify message for TLS 1.3
*/
Certificate_Verify_13::Certificate_Verify_13(const Certificate_13& certificate_msg,
                                             const std::vector<Signature_Scheme>& peer_allowed_schemes,
                                             std::string_view hostname,
                                             const Transcript_Hash& hash,
                                             Connection_Side whoami,
                                             Credentials_Manager& creds_mgr,
                                             const Policy& policy,
                                             Callbacks& callbacks,
                                             RandomNumberGenerator& rng) :
      m_side(whoami) {
   BOTAN_ASSERT_NOMSG(!certificate_msg.empty());
 
   const std::string op_type((m_side == Connection_Side::Client) ? "tls-client" : "tls-server");
   const auto context = std::string(hostname);
 
   const auto private_key = (certificate_msg.has_certificate_chain())
                               ? creds_mgr.private_key_for(certificate_msg.leaf(), op_type, context)
                               : creds_mgr.private_key_for(*certificate_msg.public_key(), op_type, context);
   if(!private_key) {
      throw TLS_Exception(Alert::InternalError, "Application did not provide a private key for its credential");
   }
 
   m_scheme = choose_signature_scheme(*private_key, policy.allowed_signature_schemes(), peer_allowed_schemes);
   BOTAN_ASSERT_NOMSG(m_scheme.is_available());
   BOTAN_ASSERT_NOMSG(m_scheme.is_compatible_with(Protocol_Version::TLS_V13));
 
   m_signature = callbacks.tls_sign_message(
      *private_key, rng, m_scheme.padding_string(), m_scheme.format().value(), message(m_side, hash));
}
 
Certificate_Verify_13::Certificate_Verify_13(const std::vector<uint8_t>& buf, const Connection_Side side) :
      Certificate_Verify(buf), m_side(side) {
   if(!m_scheme.is_available()) {
      throw TLS_Exception(Alert::IllegalParameter, "Peer sent unknown signature scheme");
   }
 
   if(!m_scheme.is_compatible_with(Protocol_Version::TLS_V13)) {
      throw TLS_Exception(Alert::IllegalParameter, "Peer sent signature algorithm that is not suitable for TLS 1.3");
   }
}
 
/*
* Verify a Certificate Verify message
*/
bool Certificate_Verify_13::verify(const Public_Key& public_key,
                                   Callbacks& callbacks,
                                   const Transcript_Hash& transcript_hash) const {
   BOTAN_ASSERT_NOMSG(m_scheme.is_available());
 
   // RFC 8446 4.2.3
   //    The keys found in certificates MUST [...] be of appropriate type for
   //    the signature algorithms they are used with.
   if(m_scheme.key_algorithm_identifier() != public_key.algorithm_identifier()) {
      throw TLS_Exception(Alert::IllegalParameter, "Signature algorithm does not match certificate's public key");
   }
 
   const bool signature_valid = callbacks.tls_verify_message(
      public_key, m_scheme.padding_string(), m_scheme.format().value(), message(m_side, transcript_hash), m_signature);
 
#if defined(BOTAN_UNSAFE_FUZZER_MODE)
   BOTAN_UNUSED(signature_valid);
   return true;
#else
   return signature_valid;
#endif
}
 
}  // namespace Botan::TLS