pk_ops.cpp

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/*
* PK Operation Types
* (C) 2010,2015,2023 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/pk_ops_impl.h>
 
#include <botan/hash.h>
#include <botan/kdf.h>
#include <botan/rng.h>
#include <botan/internal/bit_ops.h>
#include <botan/internal/eme.h>
#include <botan/internal/fmt.h>
#include <botan/internal/parsing.h>
#include <botan/internal/scan_name.h>
 
#if defined(BOTAN_HAS_RAW_HASH_FN)
   #include <botan/internal/raw_hash.h>
#endif
 
namespace Botan {
 
AlgorithmIdentifier PK_Ops::Signature::algorithm_identifier() const {
   throw Not_Implemented("This signature scheme does not have an algorithm identifier available");
}
 
PK_Ops::Encryption_with_EME::Encryption_with_EME(std::string_view eme) : m_eme(EME::create(eme)) {}
 
PK_Ops::Encryption_with_EME::~Encryption_with_EME() = default;
 
size_t PK_Ops::Encryption_with_EME::max_input_bits() const {
   return 8 * m_eme->maximum_input_size(max_ptext_input_bits());
}
 
std::vector<uint8_t> PK_Ops::Encryption_with_EME::encrypt(std::span<const uint8_t> msg, RandomNumberGenerator& rng) {
   const size_t max_input_bits = max_ptext_input_bits();
   const size_t max_input_bytes = (max_input_bits + 7) / 8;
   BOTAN_ARG_CHECK(msg.size() <= max_input_bytes, "Plaintext too large");
 
   secure_vector<uint8_t> eme_output(max_input_bits);
   const size_t written = m_eme->pad(eme_output, msg, max_input_bits, rng);
   return raw_encrypt(std::span{eme_output}.first(written), rng);
}
 
PK_Ops::Decryption_with_EME::Decryption_with_EME(std::string_view eme) : m_eme(EME::create(eme)) {}
 
PK_Ops::Decryption_with_EME::~Decryption_with_EME() = default;
 
secure_vector<uint8_t> PK_Ops::Decryption_with_EME::decrypt(uint8_t& valid_mask, std::span<const uint8_t> ctext) {
   const secure_vector<uint8_t> raw = raw_decrypt(ctext);
 
   secure_vector<uint8_t> ptext(raw.size());
   auto len = m_eme->unpad(ptext, raw);
 
   valid_mask = CT::Mask<uint8_t>::from_choice(len.has_value()).if_set_return(0xFF);
 
   /*
   This is potentially not const time, depending on how std::vector is
   implemented. But since we are always reducing length, it should
   just amount to setting the member var holding the length. Resizing
   downwards is guaranteed to not change the capacity, and since we
   set ctext to the maximum possible size (equal to the raw input) we
   know that this is always, if anything, resizing smaller than the
   capacity, so no reallocation occurs.
   */
 
   ptext.resize(len.value_or(0));
   return ptext;
}
 
PK_Ops::Key_Agreement_with_KDF::Key_Agreement_with_KDF(std::string_view kdf) {
   if(kdf != "Raw") {
      m_kdf = KDF::create_or_throw(kdf);
   }
}
 
PK_Ops::Key_Agreement_with_KDF::~Key_Agreement_with_KDF() = default;
 
secure_vector<uint8_t> PK_Ops::Key_Agreement_with_KDF::agree(size_t key_len,
                                                             std::span<const uint8_t> other_key,
                                                             std::span<const uint8_t> salt) {
   if(!salt.empty() && m_kdf == nullptr) {
      throw Invalid_Argument("PK_Key_Agreement::derive_key requires a KDF to use a salt");
   }
 
   secure_vector<uint8_t> z = raw_agree(other_key.data(), other_key.size());
   if(m_kdf) {
      return m_kdf->derive_key(key_len, z, salt.data(), salt.size());
   }
   return z;
}
 
namespace {
 
std::unique_ptr<HashFunction> create_signature_hash(std::string_view padding) {
   if(auto hash = HashFunction::create(padding)) {
      return hash;
   }
 
   SCAN_Name req(padding);
 
   if(req.algo_name() == "EMSA1" && req.arg_count() == 1) {
      if(auto hash = HashFunction::create(req.arg(0))) {
         return hash;
      }
   }
 
#if defined(BOTAN_HAS_RAW_HASH_FN)
   if(req.algo_name() == "Raw") {
      if(req.arg_count() == 0) {
         return std::make_unique<RawHashFunction>("Raw", 0);
      }
 
      if(req.arg_count() == 1) {
         if(auto hash = HashFunction::create(req.arg(0))) {
            return std::make_unique<RawHashFunction>(std::move(hash));
         }
      }
   }
#endif
 
   throw Algorithm_Not_Found(padding);
}
 
}  // namespace
 
PK_Ops::Signature_with_Hash::Signature_with_Hash(std::string_view hash) :
      Signature(), m_hash(create_signature_hash(hash)) {}
 
PK_Ops::Signature_with_Hash::~Signature_with_Hash() = default;
 
#if defined(BOTAN_HAS_RFC6979_GENERATOR)
std::string PK_Ops::Signature_with_Hash::rfc6979_hash_function() const {
   std::string hash = m_hash->name();
   if(hash != "Raw") {
      return hash;
   }
   return "SHA-512";
}
#endif
 
std::string PK_Ops::Signature_with_Hash::hash_function() const {
   return m_hash->name();
}
 
void PK_Ops::Signature_with_Hash::update(std::span<const uint8_t> msg) {
   m_hash->update(msg);
}
 
std::vector<uint8_t> PK_Ops::Signature_with_Hash::sign(RandomNumberGenerator& rng) {
   const std::vector<uint8_t> msg = m_hash->final_stdvec();
   return raw_sign(msg, rng);
}
 
PK_Ops::Verification_with_Hash::Verification_with_Hash(std::string_view padding) :
      Verification(), m_hash(create_signature_hash(padding)) {}
 
PK_Ops::Verification_with_Hash::~Verification_with_Hash() = default;
 
std::string PK_Ops::Verification_with_Hash::hash_function() const {
   return m_hash->name();
}
 
PK_Ops::Verification_with_Hash::Verification_with_Hash(const AlgorithmIdentifier& alg_id,
                                                       std::string_view pk_algo,
                                                       bool allow_null_parameters) {
   const auto oid_info = split_on(alg_id.oid().to_formatted_string(), '/');
 
   if(oid_info.size() != 2 || oid_info[0] != pk_algo) {
      throw Decoding_Error(
         fmt("Unexpected AlgorithmIdentifier OID {} in association with {} key", alg_id.oid(), pk_algo));
   }
 
   if(!alg_id.parameters_are_empty()) {
      if(alg_id.parameters_are_null()) {
         if(!allow_null_parameters) {
            throw Decoding_Error(fmt("Unexpected NULL AlgorithmIdentifier parameters for {}", pk_algo));
         }
      } else {
         throw Decoding_Error(fmt("Unexpected AlgorithmIdentifier parameters for {}", pk_algo));
      }
   }
 
   m_hash = HashFunction::create_or_throw(oid_info[1]);
}
 
void PK_Ops::Verification_with_Hash::update(std::span<const uint8_t> msg) {
   m_hash->update(msg);
}
 
bool PK_Ops::Verification_with_Hash::is_valid_signature(std::span<const uint8_t> sig) {
   const std::vector<uint8_t> msg = m_hash->final_stdvec();
   return verify(msg, sig);
}
 
size_t PK_Ops::KEM_Encryption_with_KDF::shared_key_length(size_t desired_shared_key_len) const {
   if(m_kdf) {
      return desired_shared_key_len;
   } else {
      return this->raw_kem_shared_key_length();
   }
}
 
void PK_Ops::KEM_Encryption_with_KDF::kem_encrypt(std::span<uint8_t> out_encapsulated_key,
                                                  std::span<uint8_t> out_shared_key,
                                                  RandomNumberGenerator& rng,
                                                  size_t desired_shared_key_len,
                                                  std::span<const uint8_t> salt) {
   BOTAN_ARG_CHECK(salt.empty() || m_kdf, "PK_KEM_Encryptor::encrypt requires a KDF to use a salt");
   BOTAN_ASSERT_NOMSG(out_encapsulated_key.size() == encapsulated_key_length());
 
   if(m_kdf) {
      BOTAN_ASSERT_EQUAL(
         out_shared_key.size(), desired_shared_key_len, "KDF output length and shared key length match");
 
      secure_vector<uint8_t> raw_shared(raw_kem_shared_key_length());
      this->raw_kem_encrypt(out_encapsulated_key, raw_shared, rng);
      m_kdf->derive_key(out_shared_key, raw_shared, salt, {});
   } else {
      BOTAN_ASSERT_EQUAL(out_shared_key.size(), raw_kem_shared_key_length(), "Shared key has raw KEM output length");
      this->raw_kem_encrypt(out_encapsulated_key, out_shared_key, rng);
   }
}
 
PK_Ops::KEM_Encryption_with_KDF::KEM_Encryption_with_KDF(std::string_view kdf) {
   if(kdf != "Raw") {
      m_kdf = KDF::create_or_throw(kdf);
   }
}
 
PK_Ops::KEM_Encryption_with_KDF::~KEM_Encryption_with_KDF() = default;
 
size_t PK_Ops::KEM_Decryption_with_KDF::shared_key_length(size_t desired_shared_key_len) const {
   if(m_kdf) {
      return desired_shared_key_len;
   } else {
      return this->raw_kem_shared_key_length();
   }
}
 
void PK_Ops::KEM_Decryption_with_KDF::kem_decrypt(std::span<uint8_t> out_shared_key,
                                                  std::span<const uint8_t> encapsulated_key,
                                                  size_t desired_shared_key_len,
                                                  std::span<const uint8_t> salt) {
   BOTAN_ARG_CHECK(salt.empty() || m_kdf, "PK_KEM_Decryptor::decrypt requires a KDF to use a salt");
 
   if(m_kdf) {
      BOTAN_ASSERT_EQUAL(
         out_shared_key.size(), desired_shared_key_len, "KDF output length and shared key length match");
 
      secure_vector<uint8_t> raw_shared(raw_kem_shared_key_length());
      this->raw_kem_decrypt(raw_shared, encapsulated_key);
      m_kdf->derive_key(out_shared_key, raw_shared, salt, {});
   } else {
      BOTAN_ASSERT_EQUAL(out_shared_key.size(), raw_kem_shared_key_length(), "Shared key has raw KEM output length");
      this->raw_kem_decrypt(out_shared_key, encapsulated_key);
   }
}
 
PK_Ops::KEM_Decryption_with_KDF::KEM_Decryption_with_KDF(std::string_view kdf) {
   if(kdf != "Raw") {
      m_kdf = KDF::create_or_throw(kdf);
   }
}
 
PK_Ops::KEM_Decryption_with_KDF::~KEM_Decryption_with_KDF() = default;
 
}  // namespace Botan