hmac_drbg.cpp

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/*
* HMAC_DRBG
* (C) 2014,2015,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/hmac_drbg.h>
 
#include <botan/internal/fmt.h>
#include <algorithm>
 
namespace Botan {
 
namespace {
 
size_t hmac_drbg_security_level(size_t mac_output_length) {
   // security strength of the hash function
   // for pre-image resistance (see NIST SP 800-57)
   // SHA-1: 128 bits
   // SHA-224, SHA-512/224: 192 bits,
   // SHA-256, SHA-512/256, SHA-384, SHA-512: >= 256 bits
   // NIST SP 800-90A only supports up to 256 bits though
 
   if(mac_output_length < 32) {
      return (mac_output_length - 4) * 8;
   } else {
      return 32 * 8;
   }
}
 
void check_limits(size_t reseed_interval, size_t max_number_of_bytes_per_request) {
   // SP800-90A permits up to 2^48, but it is not usable on 32 bit
   // platforms, so we only allow up to 2^24, which is still reasonably high
   if(reseed_interval == 0 || reseed_interval > static_cast<size_t>(1) << 24) {
      throw Invalid_Argument("Invalid value for reseed_interval");
   }
 
   if(max_number_of_bytes_per_request == 0 || max_number_of_bytes_per_request > 64 * 1024) {
      throw Invalid_Argument("Invalid value for max_number_of_bytes_per_request");
   }
}
 
}  // namespace
 
HMAC_DRBG::HMAC_DRBG(std::unique_ptr<MessageAuthenticationCode> prf,
                     RandomNumberGenerator& underlying_rng,
                     size_t reseed_interval,
                     size_t max_number_of_bytes_per_request) :
      Stateful_RNG(underlying_rng, reseed_interval),
      m_mac(std::move(prf)),
      m_max_number_of_bytes_per_request(max_number_of_bytes_per_request),
      m_security_level(hmac_drbg_security_level(m_mac->output_length())) {
   BOTAN_ASSERT_NONNULL(m_mac);
 
   check_limits(reseed_interval, max_number_of_bytes_per_request);
 
   clear();
}
 
HMAC_DRBG::HMAC_DRBG(std::unique_ptr<MessageAuthenticationCode> prf,
                     RandomNumberGenerator& underlying_rng,
                     Entropy_Sources& entropy_sources,
                     size_t reseed_interval,
                     size_t max_number_of_bytes_per_request) :
      Stateful_RNG(underlying_rng, entropy_sources, reseed_interval),
      m_mac(std::move(prf)),
      m_max_number_of_bytes_per_request(max_number_of_bytes_per_request),
      m_security_level(hmac_drbg_security_level(m_mac->output_length())) {
   BOTAN_ASSERT_NONNULL(m_mac);
 
   check_limits(reseed_interval, max_number_of_bytes_per_request);
 
   clear();
}
 
HMAC_DRBG::HMAC_DRBG(std::unique_ptr<MessageAuthenticationCode> prf,
                     Entropy_Sources& entropy_sources,
                     size_t reseed_interval,
                     size_t max_number_of_bytes_per_request) :
      Stateful_RNG(entropy_sources, reseed_interval),
      m_mac(std::move(prf)),
      m_max_number_of_bytes_per_request(max_number_of_bytes_per_request),
      m_security_level(hmac_drbg_security_level(m_mac->output_length())) {
   BOTAN_ASSERT_NONNULL(m_mac);
 
   check_limits(reseed_interval, max_number_of_bytes_per_request);
 
   clear();
}
 
HMAC_DRBG::HMAC_DRBG(std::unique_ptr<MessageAuthenticationCode> prf) :
      Stateful_RNG(),
      m_mac(std::move(prf)),
      m_max_number_of_bytes_per_request(64 * 1024),
      m_security_level(hmac_drbg_security_level(m_mac->output_length())) {
   BOTAN_ASSERT_NONNULL(m_mac);
   clear();
}
 
HMAC_DRBG::HMAC_DRBG(std::string_view hmac_hash) :
      Stateful_RNG(),
      m_mac(MessageAuthenticationCode::create_or_throw(fmt("HMAC({})", hmac_hash))),
      m_max_number_of_bytes_per_request(64 * 1024),
      m_security_level(hmac_drbg_security_level(m_mac->output_length())) {
   clear();
}
 
void HMAC_DRBG::clear_state() {
   if(m_V.empty()) {
      const size_t output_length = m_mac->output_length();
      m_V.resize(output_length);
      m_T.resize(output_length);
   }
 
   for(size_t i = 0; i != m_V.size(); ++i) {
      m_V[i] = 0x01;
   }
   m_mac->set_key(std::vector<uint8_t>(m_V.size(), 0x00));
}
 
std::string HMAC_DRBG::name() const {
   return fmt("HMAC_DRBG({})", m_mac->name());
}
 
/*
* HMAC_DRBG generation
* See NIST SP800-90A section 10.1.2.5
*/
void HMAC_DRBG::generate_output(std::span<uint8_t> output, std::span<const uint8_t> input) {
   BOTAN_ASSERT_NOMSG(!output.empty());
 
   if(!input.empty()) {
      update(input);
   }
 
   while(!output.empty()) {
      const size_t to_copy = std::min(output.size(), m_V.size());
      m_mac->update(m_V);
      m_mac->final(m_V);
      copy_mem(output.data(), m_V.data(), to_copy);
 
      output = output.subspan(to_copy);
   }
 
   update(input);
}
 
/*
* Reset V and the mac key with new values
* See NIST SP800-90A section 10.1.2.2
*/
void HMAC_DRBG::update(std::span<const uint8_t> input) {
   m_mac->update(m_V);
   m_mac->update(0x00);
   if(!input.empty()) {
      m_mac->update(input);
   }
   m_mac->final(m_T);
   m_mac->set_key(m_T);
 
   m_mac->update(m_V);
   m_mac->final(m_V);
 
   if(!input.empty()) {
      m_mac->update(m_V);
      m_mac->update(0x01);
      m_mac->update(input);
      m_mac->final(m_T);
      m_mac->set_key(m_T);
 
      m_mac->update(m_V);
      m_mac->final(m_V);
   }
}
 
size_t HMAC_DRBG::security_level() const {
   return m_security_level;
}
}  // namespace Botan