Botan::HMAC_DRBG Class Reference

#include <hmac_drbg.h>

Inheritance diagram for Botan::HMAC_DRBG:

Public Member Functions
bool	accepts_input () const overridefinal
void	add_entropy (const uint8_t input[], size_t input_len) override
template<typename T >
void	add_entropy_T (const T &t)
void	clear () override
void	force_reseed ()
	HMAC_DRBG (std::unique_ptr< MessageAuthenticationCode > prf)
	HMAC_DRBG (std::unique_ptr< MessageAuthenticationCode > prf, RandomNumberGenerator &underlying_rng, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL, size_t max_number_of_bytes_per_request=64 *1024)
	HMAC_DRBG (std::unique_ptr< MessageAuthenticationCode > prf, Entropy_Sources &entropy_sources, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL, size_t max_number_of_bytes_per_request=64 *1024)
	HMAC_DRBG (std::unique_ptr< MessageAuthenticationCode > prf, RandomNumberGenerator &underlying_rng, Entropy_Sources &entropy_sources, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL, size_t max_number_of_bytes_per_request=64 *1024)
	HMAC_DRBG (const std::string &hmac_hash)
void	initialize_with (const uint8_t input[], size_t length)
bool	is_seeded () const overridefinal
size_t	max_number_of_bytes_per_request () const override
std::string	name () const override
uint8_t	next_byte ()
uint8_t	next_nonzero_byte ()
secure_vector< uint8_t >	random_vec (size_t bytes)
template<typename Alloc >
void	random_vec (std::vector< uint8_t, Alloc > &v, size_t bytes)
void	randomize (uint8_t output[], size_t output_len) override
void	randomize_with_input (uint8_t output[], size_t output_len, const uint8_t input[], size_t input_len) override
void	randomize_with_ts_input (uint8_t output[], size_t output_len) overridefinal
size_t	reseed (Entropy_Sources &srcs, size_t poll_bits=BOTAN_RNG_RESEED_POLL_BITS, std::chrono::milliseconds poll_timeout=BOTAN_RNG_RESEED_DEFAULT_TIMEOUT) override
void	reseed_from_rng (RandomNumberGenerator &rng, size_t poll_bits=BOTAN_RNG_RESEED_POLL_BITS) overridefinal
size_t	reseed_interval () const
size_t	security_level () const override

Static Public Member Functions
static RandomNumberGenerator *	make_rng ()

Protected Member Functions
void	reseed_check ()
void	reset_reseed_counter ()

Detailed Description

HMAC_DRBG from NIST SP800-90A

Definition at line 21 of file hmac_drbg.h.

Constructor & Destructor Documentation

Botan::HMAC_DRBG::HMAC_DRBG ( std::unique_ptr< MessageAuthenticationCode >  prf )

explicit

Initialize an HMAC_DRBG instance with the given MAC as PRF (normally HMAC)

Automatic reseeding is disabled completely, as it has no access to any source for seed material.

If a fork is detected, the RNG will be unable to reseed itself in response. In this case, an exception will be thrown rather than generating duplicated output.

Definition at line 79 of file hmac_drbg.cpp.

References BOTAN_ASSERT_NONNULL, and clear().

                                                                 :
   Stateful_RNG(),
   m_mac(std::move(prf)),
   m_max_number_of_bytes_per_request(64*1024)
   {
   BOTAN_ASSERT_NONNULL(m_mac);
   clear();
   }

Botan::HMAC_DRBG::HMAC_DRBG	(	std::unique_ptr< MessageAuthenticationCode >	prf,
		RandomNumberGenerator &	underlying_rng,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL,
		size_t	max_number_of_bytes_per_request = 64 * 1024
	)

Initialize an HMAC_DRBG instance with the given MAC as PRF (normally HMAC)

Automatic reseeding from underlying_rng will take place after reseed_interval many requests or after a fork was detected.

Parameters

prf	MAC to use as a PRF
underlying_rng	is a reference to some RNG which will be used to perform the periodic reseeding
reseed_interval	specifies a limit of how many times the RNG will be called before automatic reseeding is performed (max. 2^24)
max_number_of_bytes_per_request	requests that are in size higher than max_number_of_bytes_per_request are treated as if multiple single requests of max_number_of_bytes_per_request size had been made. In theory SP 800-90A requires that we reject any request for a DRBG output longer than max_number_of_bytes_per_request. To avoid inconveniencing the caller who wants an output larger than max_number_of_bytes_per_request, instead treat these requests as if multiple requests of max_number_of_bytes_per_request size had been made. NIST requires for HMAC_DRBG that every implementation set a value no more than 2**19 bits (or 64 KiB). Together with reseed_interval = 1 you can enforce that for example every 512 bit automatic reseeding occurs.

Definition at line 33 of file hmac_drbg.cpp.

References BOTAN_ASSERT_NONNULL, and clear().

                                                             :
   Stateful_RNG(underlying_rng, reseed_interval),
   m_mac(std::move(prf)),
   m_max_number_of_bytes_per_request(max_number_of_bytes_per_request)
   {
   BOTAN_ASSERT_NONNULL(m_mac);

   check_limits(reseed_interval, max_number_of_bytes_per_request);

   clear();
   }

Botan::HMAC_DRBG::HMAC_DRBG	(	std::unique_ptr< MessageAuthenticationCode >	prf,
		Entropy_Sources &	entropy_sources,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL,
		size_t	max_number_of_bytes_per_request = 64 * 1024
	)

Initialize an HMAC_DRBG instance with the given MAC as PRF (normally HMAC)

Automatic reseeding from entropy_sources will take place after reseed_interval many requests or after a fork was detected.

Parameters

prf	MAC to use as a PRF
entropy_sources	will be polled to perform reseeding periodically
reseed_interval	specifies a limit of how many times the RNG will be called before automatic reseeding is performed (max. 2^24)
max_number_of_bytes_per_request	requests that are in size higher than max_number_of_bytes_per_request are treated as if multiple single requests of max_number_of_bytes_per_request size had been made. In theory SP 800-90A requires that we reject any request for a DRBG output longer than max_number_of_bytes_per_request. To avoid inconveniencing the caller who wants an output larger than max_number_of_bytes_per_request, instead treat these requests as if multiple requests of max_number_of_bytes_per_request size had been made. NIST requires for HMAC_DRBG that every implementation set a value no more than 2**19 bits (or 64 KiB). Together with reseed_interval = 1 you can enforce that for example every 512 bit automatic reseeding occurs.

Definition at line 64 of file hmac_drbg.cpp.

References BOTAN_ASSERT_NONNULL, and clear().

                                                             :
   Stateful_RNG(entropy_sources, reseed_interval),
   m_mac(std::move(prf)),
   m_max_number_of_bytes_per_request(max_number_of_bytes_per_request)
   {
   BOTAN_ASSERT_NONNULL(m_mac);

   check_limits(reseed_interval, max_number_of_bytes_per_request);

   clear();
   }

Botan::HMAC_DRBG::HMAC_DRBG	(	std::unique_ptr< MessageAuthenticationCode >	prf,
		RandomNumberGenerator &	underlying_rng,
		Entropy_Sources &	entropy_sources,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL,
		size_t	max_number_of_bytes_per_request = 64 * 1024
	)

Initialize an HMAC_DRBG instance with the given MAC as PRF (normally HMAC)

Automatic reseeding from underlying_rng and entropy_sources will take place after reseed_interval many requests or after a fork was detected.

Parameters

prf	MAC to use as a PRF
underlying_rng	is a reference to some RNG which will be used to perform the periodic reseeding
entropy_sources	will be polled to perform reseeding periodically
reseed_interval	specifies a limit of how many times the RNG will be called before automatic reseeding is performed (max. 2^24)
max_number_of_bytes_per_request	requests that are in size higher than max_number_of_bytes_per_request are treated as if multiple single requests of max_number_of_bytes_per_request size had been made. In theory SP 800-90A requires that we reject any request for a DRBG output longer than max_number_of_bytes_per_request. To avoid inconveniencing the caller who wants an output larger than max_number_of_bytes_per_request, instead treat these requests as if multiple requests of max_number_of_bytes_per_request size had been made. NIST requires for HMAC_DRBG that every implementation set a value no more than 2**19 bits (or 64 KiB). Together with reseed_interval = 1 you can enforce that for example every 512 bit automatic reseeding occurs.

Definition at line 48 of file hmac_drbg.cpp.

References BOTAN_ASSERT_NONNULL, and clear().

                                                             :
   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)
   {
   BOTAN_ASSERT_NONNULL(m_mac);

   check_limits(reseed_interval, max_number_of_bytes_per_request);

   clear();
   }

Botan::HMAC_DRBG::HMAC_DRBG ( const std::string &  hmac_hash )

inlineexplicit

Constructor taking a string for the hash

Definition at line 125 of file hmac_drbg.h.

                                                     :
         Stateful_RNG(),
         m_mac(MessageAuthenticationCode::create_or_throw("HMAC(" + hmac_hash + ")")),
         m_max_number_of_bytes_per_request(64 * 1024)
         {
         clear();
         }

Member Function Documentation

bool Botan::Stateful_RNG::accepts_input ( ) const

inlinefinaloverridevirtualinherited

Returns false if it is known that this RNG object is not able to accept externally provided inputs (via add_entropy, randomize_with_input, etc). In this case, any such provided inputs are ignored.

If this function returns true, then inputs may or may not be accepted.

Implements Botan::RandomNumberGenerator.

Definition at line 78 of file stateful_rng.h.

{ return true; }

void Botan::HMAC_DRBG::add_entropy ( const uint8_t  input[], size_t  length  )

overridevirtual

Incorporate some additional data into the RNG state. For example adding nonces or timestamps from a peer's protocol message can help hedge against VM state rollback attacks. A few RNG types do not accept any externally provided input, in which case this function is a no-op.

Parameters

input	a byte array containg the entropy to be added
length	the length of the byte array in

Implements Botan::RandomNumberGenerator.

Definition at line 174 of file hmac_drbg.cpp.

References Botan::Stateful_RNG::reset_reseed_counter(), and security_level().

   {
   update(input, input_len);

   if(8*input_len >= security_level())
      {
      reset_reseed_counter();
      }
   }

template<typename T >

void Botan::RandomNumberGenerator::add_entropy_T ( const T &  t )

inlineinherited

Incorporate some additional data into the RNG state.

Definition at line 68 of file rng.h.

References T.

Referenced by Botan::Win32_EntropySource::poll().

         {
         this->add_entropy(reinterpret_cast<const uint8_t*>(&t), sizeof(T));
         }

void Botan::HMAC_DRBG::clear ( )

overridevirtual

Clear all internally held values of this RNG

Postcondition

is_seeded() == false

Implements Botan::RandomNumberGenerator.

Definition at line 88 of file hmac_drbg.cpp.

References Botan::Stateful_RNG::clear().

Referenced by HMAC_DRBG().

   {
   Stateful_RNG::clear();

   const size_t output_length = m_mac->output_length();

   m_V.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>(output_length, 0x00));
   }

void Botan::Stateful_RNG::force_reseed ( )

inherited

Mark state as requiring a reseed on next use

Definition at line 23 of file stateful_rng.cpp.

   {
   m_reseed_counter = 0;
   }

void Botan::Stateful_RNG::initialize_with ( const uint8_t  input[], size_t  length  )

inherited

Consume this input and mark the RNG as initialized regardless of the length of the input or the current seeded state of the RNG.

Definition at line 33 of file stateful_rng.cpp.

References Botan::RandomNumberGenerator::add_entropy(), Botan::Stateful_RNG::reset_reseed_counter(), and Botan::Stateful_RNG::security_level().

   {
   add_entropy(input, len);

   if(8*len >= security_level())
      {
      reset_reseed_counter();
      }
   }

bool Botan::Stateful_RNG::is_seeded ( ) const

finaloverridevirtualinherited

Check whether this RNG is seeded.

Returns

true if this RNG was already seeded, false otherwise.

Implements Botan::RandomNumberGenerator.

Definition at line 28 of file stateful_rng.cpp.

Referenced by Botan::Stateful_RNG::reseed_check().

   {
   return m_reseed_counter > 0;
   }

RandomNumberGenerator * Botan::RandomNumberGenerator::make_rng ( )

staticinherited

Create a seeded and active RNG object for general application use Added in 1.8.0 Use AutoSeeded_RNG instead

Definition at line 69 of file rng.cpp.

   {
#if defined(BOTAN_HAS_AUTO_SEEDING_RNG)
   return new AutoSeeded_RNG;
#else
   throw Not_Implemented("make_rng failed, no AutoSeeded_RNG in this build");
#endif
   }

size_t Botan::HMAC_DRBG::max_number_of_bytes_per_request ( ) const

inlineoverridevirtual

Some DRBGs have a notion of the maximum number of bytes per request. Longer requests (to randomize) will be treated as multiple requests, and may initiate reseeding multiple times, depending on the values of max_number_of_bytes_per_request and reseed_interval(). This function returns zero if the RNG in question does not have such a notion.

Returns

max number of bytes per request (or zero)

Implements Botan::Stateful_RNG.

Definition at line 146 of file hmac_drbg.h.

         { return m_max_number_of_bytes_per_request; }

std::string Botan::HMAC_DRBG::name ( ) const

overridevirtual

Returns

the name of this RNG type

Implements Botan::RandomNumberGenerator.

Definition at line 100 of file hmac_drbg.cpp.

   {
   return "HMAC_DRBG(" + m_mac->name() + ")";
   }

uint8_t Botan::RandomNumberGenerator::next_byte ( )

inlineinherited

Return a random byte

Returns

random byte

Definition at line 159 of file rng.h.

Referenced by Botan::random_prime().

         {
         uint8_t b;
         this->randomize(&b, 1);
         return b;
         }

uint8_t Botan::RandomNumberGenerator::next_nonzero_byte ( )

inlineinherited

Returns

a random byte that is greater than zero

Definition at line 169 of file rng.h.

Referenced by Botan::EME_PKCS1v15::pad().

         {
         uint8_t b = this->next_byte();
         while(b == 0)
            b = this->next_byte();
         return b;
         }

secure_vector<uint8_t> Botan::RandomNumberGenerator::random_vec ( size_t  bytes )

inlineinherited

Return a random vector

Parameters

bytes

number of bytes in the result

Returns

randomized vector of length bytes

Definition at line 141 of file rng.h.

Referenced by Botan::CECPQ1_accept(), Botan::CECPQ1_offer(), Botan::TLS::Client_Key_Exchange::Client_Key_Exchange(), Botan::Curve25519_PrivateKey::Curve25519_PrivateKey(), Botan::PK_Decryptor::decrypt_or_random(), Botan::Ed25519_PrivateKey::Ed25519_PrivateKey(), Botan::TLS::Session::encrypt(), Botan::KeyPair::encryption_consistency_check(), Botan::generate_bcrypt(), Botan::mceies_encrypt(), Botan::OctetString::OctetString(), Botan::BigInt::randomize(), Botan::TLS::Session_Manager_In_Memory::remove_all(), and Botan::TLS::Session_Manager_SQL::Session_Manager_SQL().

         {
         secure_vector<uint8_t> output;
         random_vec(output, bytes);
         return output;
         }

template<typename Alloc >

void Botan::RandomNumberGenerator::random_vec ( std::vector< uint8_t, Alloc > &  v, size_t  bytes  )

inlineinherited

Definition at line 149 of file rng.h.

         {
         v.resize(bytes);
         this->randomize(v.data(), v.size());
         }

void Botan::HMAC_DRBG::randomize ( uint8_t  output[], size_t  length  )

overridevirtual

Randomize a byte array.

Parameters

output	the byte array to hold the random output.
length	the length of the byte array output in bytes.

Implements Botan::RandomNumberGenerator.

Definition at line 105 of file hmac_drbg.cpp.

References randomize_with_input().

   {
   randomize_with_input(output, output_len, nullptr, 0);
   }

void Botan::HMAC_DRBG::randomize_with_input ( uint8_t  output[], size_t  output_len, const uint8_t  input[], size_t  input_len  )

overridevirtual

Incorporate entropy into the RNG state then produce output. Some RNG types implement this using a single operation, default calls add_entropy + randomize in sequence.

Use this to further bind the outputs to your current process/protocol state. For instance if generating a new key for use in a session, include a session ID or other such value. See NIST SP 800-90 A, B, C series for more ideas.

Parameters

output	buffer to hold the random output
output_len	size of the output buffer in bytes
input	entropy buffer to incorporate
input_len	size of the input buffer in bytes

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 114 of file hmac_drbg.cpp.

References Botan::copy_mem(), and Botan::Stateful_RNG::reseed_check().

Referenced by randomize().

   {
   while(output_len > 0)
      {
      size_t this_req = std::min(m_max_number_of_bytes_per_request, output_len);
      output_len -= this_req;

      reseed_check();

      if(input_len > 0)
         {
         update(input, input_len);
         }

      while(this_req)
         {
         const size_t to_copy = std::min(this_req, m_V.size());
         m_mac->update(m_V.data(), m_V.size());
         m_mac->final(m_V.data());
         copy_mem(output, m_V.data(), to_copy);

         output += to_copy;
         this_req -= to_copy;
         }

      update(input, input_len);
      }

   }

void Botan::Stateful_RNG::randomize_with_ts_input ( uint8_t  output[], size_t  output_len  )

finaloverridevirtualinherited

Overrides default implementation and also includes the current process ID and the reseed counter.

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 43 of file stateful_rng.cpp.

References Botan::RDRAND_RNG::available(), Botan::OS::get_high_resolution_clock(), Botan::OS::get_system_timestamp_ns(), Botan::RDRAND_RNG::randomize(), Botan::RandomNumberGenerator::randomize_with_input(), and Botan::store_le().

   {
   uint8_t additional_input[24] = { 0 };

   store_le(OS::get_high_resolution_clock(), additional_input);

#if defined(BOTAN_HAS_RDRAND_RNG)
   if(RDRAND_RNG::available())
      {
      RDRAND_RNG rdrand;
      rdrand.randomize(additional_input + 8, sizeof(additional_input) - 8);
      }
   else
#endif
      {
      store_le(OS::get_system_timestamp_ns(), additional_input + 8);
      store_le(m_last_pid, additional_input + 16);
      store_le(static_cast<uint32_t>(m_reseed_counter), additional_input + 20);
      }

   randomize_with_input(output, output_len, additional_input, sizeof(additional_input));
   }

size_t Botan::Stateful_RNG::reseed ( Entropy_Sources &  srcs, size_t  poll_bits = BOTAN_RNG_RESEED_POLL_BITS, std::chrono::milliseconds  poll_timeout = BOTAN_RNG_RESEED_DEFAULT_TIMEOUT  )

overridevirtualinherited

Poll provided sources for up to poll_bits bits of entropy or until the timeout expires. Returns estimate of the number of bits collected.

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 66 of file stateful_rng.cpp.

References Botan::RandomNumberGenerator::reseed(), Botan::Stateful_RNG::reset_reseed_counter(), and Botan::Stateful_RNG::security_level().

Referenced by Botan::Stateful_RNG::reseed_check().

   {
   size_t bits_collected = RandomNumberGenerator::reseed(srcs, poll_bits, poll_timeout);

   if(bits_collected >= security_level())
      {
      reset_reseed_counter();
      }

   return bits_collected;
   }

void Botan::Stateful_RNG::reseed_check ( )

protectedinherited

Definition at line 90 of file stateful_rng.cpp.

References BOTAN_ASSERT, Botan::OS::get_process_id(), Botan::Stateful_RNG::is_seeded(), Botan::RandomNumberGenerator::name(), Botan::Stateful_RNG::reseed(), Botan::Stateful_RNG::reseed_from_rng(), and Botan::Stateful_RNG::security_level().

Referenced by Botan::ChaCha_RNG::randomize_with_input(), and randomize_with_input().

   {
   const uint32_t cur_pid = OS::get_process_id();

   const bool fork_detected = (m_last_pid > 0) && (cur_pid != m_last_pid);

   if(is_seeded() == false ||
      fork_detected ||
      (m_reseed_interval > 0 && m_reseed_counter >= m_reseed_interval))
      {
      m_reseed_counter = 0;
      m_last_pid = cur_pid;

      if(m_underlying_rng)
         {
         reseed_from_rng(*m_underlying_rng, security_level());
         }

      if(m_entropy_sources)
         {
         reseed(*m_entropy_sources, security_level());
         }

      if(!is_seeded())
         {
         if(fork_detected)
            throw Invalid_State("Detected use of fork but cannot reseed DRBG");
         else
            throw PRNG_Unseeded(name());
         }
      }
   else
      {
      BOTAN_ASSERT(m_reseed_counter != 0, "RNG is seeded");
      m_reseed_counter += 1;
      }
   }

void Botan::Stateful_RNG::reseed_from_rng ( RandomNumberGenerator &  rng, size_t  poll_bits = BOTAN_RNG_RESEED_POLL_BITS  )

finaloverridevirtualinherited

Reseed by reading specified bits from the RNG

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 80 of file stateful_rng.cpp.

References Botan::RandomNumberGenerator::reseed_from_rng(), Botan::Stateful_RNG::reset_reseed_counter(), and Botan::Stateful_RNG::security_level().

Referenced by Botan::Stateful_RNG::reseed_check().

   {
   RandomNumberGenerator::reseed_from_rng(rng, poll_bits);

   if(poll_bits >= security_level())
      {
      reset_reseed_counter();
      }
   }

size_t Botan::Stateful_RNG::reseed_interval ( ) const

inlineinherited

Definition at line 120 of file stateful_rng.h.

{ return m_reseed_interval; }

void Botan::Stateful_RNG::reset_reseed_counter ( )

inlineprotectedinherited

Called by a subclass to notify that a reseed has been successfully performed.

Definition at line 131 of file stateful_rng.h.

Referenced by Botan::ChaCha_RNG::add_entropy(), add_entropy(), Botan::Stateful_RNG::initialize_with(), Botan::Stateful_RNG::reseed(), and Botan::Stateful_RNG::reseed_from_rng().

{ m_reseed_counter = 1; }

size_t Botan::HMAC_DRBG::security_level ( ) const

overridevirtual

Returns

intended security level of this DRBG

Implements Botan::Stateful_RNG.

Definition at line 184 of file hmac_drbg.cpp.

Referenced by add_entropy().

   {
   // security strength of the hash function
   // for pre-image resistance (see NIST SP 800-57)
   // SHA-160: 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

   const size_t output_length = m_mac->output_length();

   if(output_length < 32)
      {
      return (output_length - 4) * 8;
      }
   else
      {
      return 32 * 8;
      }
   }

---

The documentation for this class was generated from the following files:

• src/lib/rng/hmac_drbg/hmac_drbg.h
• src/lib/rng/hmac_drbg/hmac_drbg.cpp