x509_obj.cpp

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/*
* X.509 SIGNED Object
* (C) 1999-2007,2020 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/x509_obj.h>
#include <botan/pubkey.h>
#include <botan/der_enc.h>
#include <botan/ber_dec.h>
#include <botan/parsing.h>
#include <botan/pem.h>
#include <botan/emsa.h>
#include <algorithm>

namespace Botan {

namespace {
struct Pss_params
   {
   AlgorithmIdentifier hash_algo;
   AlgorithmIdentifier mask_gen_algo;
   AlgorithmIdentifier mask_gen_hash;  // redundant: decoded mask_gen_algo.parameters
   size_t salt_len;
   size_t trailer_field;
   };

Pss_params decode_pss_params(const std::vector<uint8_t>& encoded_pss_params)
   {
   const AlgorithmIdentifier default_hash("SHA-160", AlgorithmIdentifier::USE_NULL_PARAM);
   const AlgorithmIdentifier default_mgf("MGF1", default_hash.BER_encode());

   Pss_params pss_parameter;
   BER_Decoder(encoded_pss_params)
      .start_cons(SEQUENCE)
         .decode_optional(pss_parameter.hash_algo, ASN1_Tag(0), PRIVATE, default_hash)
         .decode_optional(pss_parameter.mask_gen_algo, ASN1_Tag(1), PRIVATE, default_mgf)
         .decode_optional(pss_parameter.salt_len, ASN1_Tag(2), PRIVATE, size_t(20))
         .decode_optional(pss_parameter.trailer_field, ASN1_Tag(3), PRIVATE, size_t(1))
      .end_cons();

   BER_Decoder(pss_parameter.mask_gen_algo.get_parameters()).decode(pss_parameter.mask_gen_hash);

   return pss_parameter;
   }
}

/*
* Read a PEM or BER X.509 object
*/
void X509_Object::load_data(DataSource& in)
   {
   try {
      if(ASN1::maybe_BER(in) && !PEM_Code::matches(in))
         {
         BER_Decoder dec(in);
         decode_from(dec);
         }
      else
         {
         std::string got_label;
         DataSource_Memory ber(PEM_Code::decode(in, got_label));

         if(got_label != PEM_label())
            {
            bool is_alternate = false;
            for(std::string alt_label : alternate_PEM_labels())
               {
               if(got_label == alt_label)
                  {
                  is_alternate = true;
                  break;
                  }
               }

            if(!is_alternate)
               throw Decoding_Error("Unexpected PEM label for " + PEM_label() + " of " + got_label);
            }

         BER_Decoder dec(ber);
         decode_from(dec);
         }
      }
   catch(Decoding_Error& e)
      {
      throw Decoding_Error(PEM_label() + " decoding", e);
      }
   }


void X509_Object::encode_into(DER_Encoder& to) const
   {
   to.start_cons(SEQUENCE)
         .start_cons(SEQUENCE)
            .raw_bytes(signed_body())
         .end_cons()
         .encode(signature_algorithm())
         .encode(signature(), BIT_STRING)
      .end_cons();
   }

/*
* Read a BER encoded X.509 object
*/
void X509_Object::decode_from(BER_Decoder& from)
   {
   from.start_cons(SEQUENCE)
         .start_cons(SEQUENCE)
            .raw_bytes(m_tbs_bits)
         .end_cons()
         .decode(m_sig_algo)
         .decode(m_sig, BIT_STRING)
      .end_cons();

   force_decode();
   }

/*
* Return a PEM encoded X.509 object
*/
std::string X509_Object::PEM_encode() const
   {
   return PEM_Code::encode(BER_encode(), PEM_label());
   }

/*
* Return the TBS data
*/
std::vector<uint8_t> X509_Object::tbs_data() const
   {
   return ASN1::put_in_sequence(m_tbs_bits);
   }

/*
* Return the hash used in generating the signature
*/
std::string X509_Object::hash_used_for_signature() const
   {
   const OID& oid = m_sig_algo.get_oid();
   const std::vector<std::string> sig_info = split_on(oid.to_formatted_string(), '/');

   if(sig_info.size() == 1 && sig_info[0] == "Ed25519")
      return "SHA-512";
   else if(sig_info.size() != 2)
      throw Internal_Error("Invalid name format found for " + oid.to_string());

   if(sig_info[1] == "EMSA4")
      {
      const OID hash_oid = decode_pss_params(signature_algorithm().get_parameters()).hash_algo.get_oid();
      return hash_oid.to_formatted_string();
      }
   else
      {
      const std::vector<std::string> pad_and_hash =
         parse_algorithm_name(sig_info[1]);

      if(pad_and_hash.size() != 2)
         {
         throw Internal_Error("Invalid name format " + sig_info[1]);
         }

      return pad_and_hash[1];
      }
   }

/*
* Check the signature on an object
*/
bool X509_Object::check_signature(const Public_Key* pub_key) const
   {
   if(!pub_key)
      throw Invalid_Argument("No key provided for " + PEM_label() + " signature check");
   std::unique_ptr<const Public_Key> key(pub_key);
   return check_signature(*key);
   }

bool X509_Object::check_signature(const Public_Key& pub_key) const
   {
   const Certificate_Status_Code code = verify_signature(pub_key);
   return (code == Certificate_Status_Code::VERIFIED);
   }

Certificate_Status_Code X509_Object::verify_signature(const Public_Key& pub_key) const
   {
   const std::vector<std::string> sig_info =
      split_on(m_sig_algo.get_oid().to_formatted_string(), '/');

   if(sig_info.size() < 1 || sig_info.size() > 2 || sig_info[0] != pub_key.algo_name())
      return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;

   const std::string pub_key_algo = sig_info[0];
   std::string padding;
   if(sig_info.size() == 2)
      padding = sig_info[1];
   else if(pub_key_algo == "Ed25519" || pub_key_algo == "XMSS")
      padding = "Pure";
   else
      return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;

   const Signature_Format format = pub_key.default_x509_signature_format();

   if(padding == "EMSA4")
      {
      // "MUST contain RSASSA-PSS-params"
      if(signature_algorithm().get_parameters().empty())
         {
         return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
         }

      Pss_params pss_parameter = decode_pss_params(signature_algorithm().get_parameters());

      // hash_algo must be SHA1, SHA2-224, SHA2-256, SHA2-384 or SHA2-512
      const std::string hash_algo = pss_parameter.hash_algo.get_oid().to_formatted_string();
      if(hash_algo != "SHA-160" &&
         hash_algo != "SHA-224" &&
         hash_algo != "SHA-256" &&
         hash_algo != "SHA-384" &&
         hash_algo != "SHA-512")
         {
         return Certificate_Status_Code::UNTRUSTED_HASH;
         }

      const std::string mgf_algo = pss_parameter.mask_gen_algo.get_oid().to_formatted_string();
      if(mgf_algo != "MGF1")
         {
         return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
         }

      // For MGF1, it is strongly RECOMMENDED that the underlying hash function be the same as the one identified by hashAlgorithm
      // Must be SHA1, SHA2-224, SHA2-256, SHA2-384 or SHA2-512
      if(pss_parameter.mask_gen_hash.get_oid() != pss_parameter.hash_algo.get_oid())
         {
         return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
         }

      if(pss_parameter.trailer_field != 1)
         {
         return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
         }

      padding += "(" + hash_algo + "," + mgf_algo + "," + std::to_string(pss_parameter.salt_len) + ")";
      }
   else
      {
      /*
      * For all other signature types the signature parameters should
      * be either NULL or empty. In theory there is some distinction between
      * these but in practice they seem to be used somewhat interchangeably.
      *
      * The various RFCs all have prescriptions of what is allowed:
      * RSA - NULL (RFC 3279)
      * DSA - empty (RFC 3279)
      * ECDSA - empty (RFC 3279)
      * GOST - empty (RFC 4491)
      * Ed25519 - empty (RFC 8410)
      * XMSS - empty (draft-vangeest-x509-hash-sigs)
      *
      * But in practice we find RSA with empty and ECDSA will NULL all
      * over the place so it's not really possible to enforce. For Ed25519
      * and XMSS because they are new we attempt to enforce.
      */
      if(pub_key_algo == "Ed25519" || pub_key_algo == "XMSS")
         {
         if(!signature_algorithm().parameters_are_empty())
            {
            return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
            }
         }
      else
         {
         if(!signature_algorithm().parameters_are_null_or_empty())
            {
            return Certificate_Status_Code::SIGNATURE_ALGO_BAD_PARAMS;
            }
         }
      }

   try
      {
      PK_Verifier verifier(pub_key, padding, format);
      const bool valid = verifier.verify_message(tbs_data(), signature());

      if(valid)
         return Certificate_Status_Code::VERIFIED;
      else
         return Certificate_Status_Code::SIGNATURE_ERROR;
      }
   catch(Algorithm_Not_Found&)
      {
      return Certificate_Status_Code::SIGNATURE_ALGO_UNKNOWN;
      }
   catch(...)
      {
      // This shouldn't happen, fallback to generic signature error
      return Certificate_Status_Code::SIGNATURE_ERROR;
      }
   }

/*
* Apply the X.509 SIGNED macro
*/
std::vector<uint8_t> X509_Object::make_signed(PK_Signer* signer,
                                            RandomNumberGenerator& rng,
                                            const AlgorithmIdentifier& algo,
                                            const secure_vector<uint8_t>& tbs_bits)
   {
   const std::vector<uint8_t> signature = signer->sign_message(tbs_bits, rng);

   std::vector<uint8_t> output;
   DER_Encoder(output)
      .start_cons(SEQUENCE)
         .raw_bytes(tbs_bits)
         .encode(algo)
         .encode(signature, BIT_STRING)
      .end_cons();

   return output;
   }

namespace {

std::string choose_sig_algo(AlgorithmIdentifier& sig_algo,
                            const Private_Key& key,
                            const std::string& hash_fn,
                            const std::string& user_specified)
   {
   const std::string algo_name = key.algo_name();
   std::string padding;

   // check algo_name and set default
   if(algo_name == "RSA")
      {
      // set to EMSA3 for compatibility reasons, originally it was the only option
      padding = "EMSA3(" + hash_fn + ")";
      }
   else if(algo_name == "DSA" ||
           algo_name == "ECDSA" ||
           algo_name == "ECGDSA" ||
           algo_name == "ECKCDSA" ||
           algo_name == "GOST-34.10" ||
           algo_name == "GOST-34.10-2012-256" ||
           algo_name == "GOST-34.10-2012-512")
      {
      padding = "EMSA1(" + hash_fn + ")";
      }
   else if(algo_name == "Ed25519")
      {
      padding = "Pure";
      }
   else if(algo_name == "XMSS")
      {
      if(user_specified.empty() == true)
         {
         throw Invalid_Argument("XMSS requires padding scheme");
         }
      padding = user_specified;
      sig_algo = AlgorithmIdentifier(OID::from_string("XMSS"), AlgorithmIdentifier::USE_EMPTY_PARAM);
      return padding;
      }
   else
      {
      throw Invalid_Argument("Unknown X.509 signing key type: " + algo_name);
      }

   if(user_specified.empty() == false)
      {
      padding = user_specified;
      }

   if(padding != "Pure")
      {
      // try to construct an EMSA object from the padding options or default
      std::unique_ptr<EMSA> emsa;
      try
         {
         emsa.reset(get_emsa(padding));
         }
      /*
      * get_emsa will throw if opts contains {"padding",<valid_padding>} but
      * <valid_padding> does not specify a hash function.
      * Omitting it is valid since it needs to be identical to hash_fn.
      * If it still throws, something happened that we cannot repair here,
      * e.g. the algorithm/padding combination is not supported.
      */
      catch(...)
         {
         emsa.reset(get_emsa(padding + "(" + hash_fn + ")"));
         }

      if(!emsa)
         {
         throw Invalid_Argument("Could not parse padding scheme " + padding);
         }

      sig_algo = emsa->config_for_x509(key, hash_fn);
      return emsa->name();
      }
   else
      {
      sig_algo = AlgorithmIdentifier(OID::from_string("Ed25519"), AlgorithmIdentifier::USE_EMPTY_PARAM);
      return "Pure";
      }
   }

}

/*
* Choose a signing format for the key
*/
std::unique_ptr<PK_Signer> X509_Object::choose_sig_format(AlgorithmIdentifier& sig_algo,
                                                          const Private_Key& key,
                                                          RandomNumberGenerator& rng,
                                                          const std::string& hash_fn,
                                                          const std::string& padding_algo)
   {
   const Signature_Format format = key.default_x509_signature_format();

   const std::string emsa = choose_sig_algo(sig_algo, key, hash_fn, padding_algo);

   return std::unique_ptr<PK_Signer>(new PK_Signer(key, rng, emsa, format));
   }

}