Botan::ChaCha_RNG Class Reference

#include <chacha_rng.h>

Inheritance diagram for Botan::ChaCha_RNG:

Public Member Functions
bool	accepts_input () const override final
void	add_entropy (const uint8_t input[], size_t input_len) override final
template<typename T >
void	add_entropy_T (const T &t)
	ChaCha_RNG ()
	ChaCha_RNG (const secure_vector< uint8_t > &seed)
	ChaCha_RNG (Entropy_Sources &entropy_sources, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL)
	ChaCha_RNG (RandomNumberGenerator &underlying_rng, Entropy_Sources &entropy_sources, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL)
	ChaCha_RNG (RandomNumberGenerator &underlying_rng, size_t reseed_interval=BOTAN_RNG_DEFAULT_RESEED_INTERVAL)
void	clear () override final
void	force_reseed ()
void	initialize_with (const uint8_t input[], size_t length)
bool	is_seeded () const override final
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 final
void	randomize_with_input (uint8_t output[], size_t output_len, const uint8_t input[], size_t input_len) override final
void	randomize_with_ts_input (uint8_t output[], size_t output_len) override final
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) override final
size_t	reseed_interval () const
size_t	security_level () const override

Protected Member Functions
void	reseed_check ()

Detailed Description

ChaCha_RNG is a very fast but completely ad-hoc RNG created by creating a 256-bit random value and using it as a key for ChaCha20.

The RNG maintains two 256-bit keys, one for HMAC_SHA256 (HK) and the other for ChaCha20 (CK). To compute a new key in response to reseeding request or add_entropy calls, ChaCha_RNG computes CK' = HMAC_SHA256(HK, input_material) Then a new HK' is computed by running ChaCha20 with the new key to output 32 bytes: HK' = ChaCha20(CK')

Now output can be produced by continuing to produce output with ChaCha20 under CK'

The first HK (before seeding occurs) is taken as the all zero value.

Warning

This RNG construction is probably fine but is non-standard. The primary reason to use it is in cases where the other RNGs are not fast enough.

Definition at line 40 of file chacha_rng.h.

Constructor & Destructor Documentation

ChaCha_RNG() [1/5]

Botan::ChaCha_RNG::ChaCha_RNG

(

)

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 12 of file chacha_rng.cpp.

                       : Stateful_RNG()
   {
   m_hmac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
   m_chacha = StreamCipher::create_or_throw("ChaCha(20)");
   clear();
   }

References Botan::Stateful_RNG::clear(), Botan::MessageAuthenticationCode::create_or_throw(), and Botan::StreamCipher::create_or_throw().

ChaCha_RNG() [2/5]

Botan::ChaCha_RNG::ChaCha_RNG

(

const secure_vector< uint8_t > &

seed

)

Provide an initial seed to the RNG, without providing an underlying RNG or entropy source. 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.

Parameters

seed	the seed material, should be at least 256 bits

Definition at line 19 of file chacha_rng.cpp.

                                                         : Stateful_RNG()
   {
   m_hmac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
   m_chacha = StreamCipher::create_or_throw("ChaCha(20)");
   clear();
   add_entropy(seed.data(), seed.size());
   }

References Botan::Stateful_RNG::add_entropy(), Botan::Stateful_RNG::clear(), Botan::MessageAuthenticationCode::create_or_throw(), and Botan::StreamCipher::create_or_throw().

ChaCha_RNG() [3/5]

Botan::ChaCha_RNG::ChaCha_RNG	(	RandomNumberGenerator &	underlying_rng,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL
	)

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

Parameters

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

Definition at line 27 of file chacha_rng.cpp.

                                               :
   Stateful_RNG(underlying_rng, reseed_interval)
   {
   m_hmac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
   m_chacha = StreamCipher::create_or_throw("ChaCha(20)");
   clear();
   }

References Botan::Stateful_RNG::clear(), Botan::MessageAuthenticationCode::create_or_throw(), and Botan::StreamCipher::create_or_throw().

ChaCha_RNG() [4/5]

Botan::ChaCha_RNG::ChaCha_RNG	(	Entropy_Sources &	entropy_sources,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL
	)

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

Parameters

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.

Definition at line 46 of file chacha_rng.cpp.

                                               :
   Stateful_RNG(entropy_sources, reseed_interval)
   {
   m_hmac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
   m_chacha = StreamCipher::create_or_throw("ChaCha(20)");
   clear();
   }

References Botan::Stateful_RNG::clear(), Botan::MessageAuthenticationCode::create_or_throw(), and Botan::StreamCipher::create_or_throw().

ChaCha_RNG() [5/5]

Botan::ChaCha_RNG::ChaCha_RNG	(	RandomNumberGenerator &	underlying_rng,
		Entropy_Sources &	entropy_sources,
		size_t	reseed_interval = BOTAN_RNG_DEFAULT_RESEED_INTERVAL
	)

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

Parameters

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.

Definition at line 36 of file chacha_rng.cpp.

                                               :
   Stateful_RNG(underlying_rng, entropy_sources, reseed_interval)
   {
   m_hmac = MessageAuthenticationCode::create_or_throw("HMAC(SHA-256)");
   m_chacha = StreamCipher::create_or_throw("ChaCha(20)");
   clear();
   }

References Botan::Stateful_RNG::clear(), Botan::MessageAuthenticationCode::create_or_throw(), and Botan::StreamCipher::create_or_throw().

Member Function Documentation

accepts_input()

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 79 of file stateful_rng.h.

{ return true; }

add_entropy()

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

finaloverridevirtualinherited

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

Exceptions

Exception

may throw if the RNG accepts input, but adding the entropy failed.

Implements Botan::RandomNumberGenerator.

Definition at line 37 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
 
   update(input, input_len);
 
   if(8*input_len >= security_level())
      {
      reset_reseed_counter();
      }
   }

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

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

add_entropy_T()

template<typename T >

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

inlineinherited

Incorporate some additional data into the RNG state.

Definition at line 76 of file rng.h.

         {
         static_assert(std::is_standard_layout<T>::value && std::is_trivial<T>::value, "add_entropy_T data must be POD");
         this->add_entropy(reinterpret_cast<const uint8_t*>(&t), sizeof(T));
         }

References T.

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

clear()

void Botan::Stateful_RNG::clear ( )

finaloverridevirtualinherited

Clear all internally held values of this RNG

Postcondition

is_seeded() == false if the RNG has an internal state that can be cleared.

Implements Botan::RandomNumberGenerator.

Definition at line 17 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
   m_reseed_counter = 0;
   m_last_pid = 0;
   clear_state();
   }

References Botan::Stateful_RNG::clear_state().

Referenced by ChaCha_RNG(), Botan::HMAC_DRBG::HMAC_DRBG(), and Botan::Stateful_RNG::initialize_with().

force_reseed()

void Botan::Stateful_RNG::force_reseed ( )

inherited

Mark state as requiring a reseed on next use

Definition at line 25 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
   m_reseed_counter = 0;
   }

initialize_with()

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 49 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
 
   clear();
   add_entropy(input, len);
   }

References Botan::Stateful_RNG::add_entropy(), and Botan::Stateful_RNG::clear().

is_seeded()

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 31 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
   return m_reseed_counter > 0;
   }

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

max_number_of_bytes_per_request()

size_t Botan::ChaCha_RNG::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 109 of file chacha_rng.h.

{ return 0; }

name()

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

inlineoverridevirtual

Returns

the name of this RNG type

Implements Botan::RandomNumberGenerator.

Definition at line 105 of file chacha_rng.h.

{ return "ChaCha_RNG"; }

next_byte()

uint8_t Botan::RandomNumberGenerator::next_byte ( )

inlineinherited

Return a random byte

Returns

random byte

Exceptions

PRNG_Unseeded	if the RNG fails because it has not enough entropy
Exception	if the RNG fails

Definition at line 187 of file rng.h.

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

References b.

Referenced by Botan::random_prime().

next_nonzero_byte()

uint8_t Botan::RandomNumberGenerator::next_nonzero_byte ( )

inlineinherited

Returns

a random byte that is greater than zero

Exceptions

PRNG_Unseeded	if the RNG fails because it has not enough entropy
Exception	if the RNG fails

Definition at line 199 of file rng.h.

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

References b.

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

random_vec() [1/2]

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

Exceptions

PRNG_Unseeded	if the RNG fails because it has not enough entropy
Exception	if the RNG fails

Definition at line 167 of file rng.h.

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

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::Kyber_PrivateKey::Kyber_PrivateKey(), Botan::OctetString::OctetString(), Botan::BigInt::randomize(), and Botan::TLS::Session_Manager_In_Memory::remove_all().

random_vec() [2/2]

template<typename Alloc >

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

inlineinherited

Definition at line 175 of file rng.h.

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

References v.

randomize()

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

finaloverridevirtualinherited

Randomize a byte array.

May block shortly if e.g. the RNG is not yet initialized or a retry because of insufficient entropy is needed.

Parameters

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

Exceptions

PRNG_Unseeded	if the RNG fails because it has not enough entropy
Exception	if the RNG fails

Implements Botan::RandomNumberGenerator.

Definition at line 57 of file stateful_rng.cpp.

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

References Botan::Stateful_RNG::randomize_with_input().

randomize_with_input()

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

finaloverridevirtualinherited

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

Exceptions

PRNG_Unseeded	if the RNG fails because it has not enough entropy
Exception	if the RNG fails
Exception	may throw if the RNG accepts input, but adding the entropy failed.

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 79 of file stateful_rng.cpp.

   {
   if(output_len == 0)
      return;
 
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
 
   const size_t max_per_request = max_number_of_bytes_per_request();
 
   if(max_per_request == 0) // no limit
      {
      reseed_check();
      this->generate_output(output, output_len, input, input_len);
      }
   else
      {
      while(output_len > 0)
         {
         const size_t this_req = std::min(max_per_request, output_len);
 
         /*
         * We split the request into several requests to the underlying DRBG but
         * pass the input to each invocation. It might be more sensible to only
         * provide it for the first invocation, however between 2.0 and 2.15
         * HMAC_DRBG always provided it for all requests so retain that here.
         */
 
         reseed_check();
         this->generate_output(output, this_req, input, input_len);
 
         output += this_req;
         output_len -= this_req;
         }
      }
   }

References Botan::Stateful_RNG::generate_output(), Botan::Stateful_RNG::max_number_of_bytes_per_request(), and Botan::Stateful_RNG::reseed_check().

Referenced by Botan::Stateful_RNG::randomize(), and Botan::Stateful_RNG::randomize_with_ts_input().

randomize_with_ts_input()

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 62 of file stateful_rng.cpp.

   {
   uint8_t additional_input[20] = { 0 };
 
   store_le(OS::get_high_resolution_clock(), additional_input);
 
#if defined(BOTAN_HAS_SYSTEM_RNG)
   System_RNG system_rng;
   system_rng.randomize(additional_input + 8, sizeof(additional_input) - 8);
#else
   store_le(OS::get_system_timestamp_ns(), additional_input + 8);
   store_le(OS::get_process_id(), additional_input + 16);
#endif
 
   randomize_with_input(output, output_len, additional_input, sizeof(additional_input));
   }

References Botan::OS::get_high_resolution_clock(), Botan::OS::get_process_id(), Botan::OS::get_system_timestamp_ns(), Botan::RandomNumberGenerator::randomize(), Botan::Stateful_RNG::randomize_with_input(), Botan::store_le(), and Botan::system_rng().

reseed()

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 116 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
 
   const size_t bits_collected = RandomNumberGenerator::reseed(srcs, poll_bits, poll_timeout);
 
   if(bits_collected >= security_level())
      {
      reset_reseed_counter();
      }
 
   return bits_collected;
   }

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

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

reseed_check()

void Botan::Stateful_RNG::reseed_check ( )

protectedinherited

Definition at line 150 of file stateful_rng.cpp.

   {
   // Lock is held whenever this function is called
 
   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;
      }
   }

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::Stateful_RNG::randomize_with_input().

reseed_from_rng()

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

Sets the seeded state to true if enough entropy was added.

Exceptions

Exception

if RNG accepts input but reseeding failed.

Reimplemented from Botan::RandomNumberGenerator.

Definition at line 132 of file stateful_rng.cpp.

   {
   lock_guard_type<recursive_mutex_type> lock(m_mutex);
 
   RandomNumberGenerator::reseed_from_rng(rng, poll_bits);
 
   if(poll_bits >= security_level())
      {
      reset_reseed_counter();
      }
   }

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

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

reseed_interval()

size_t Botan::Stateful_RNG::reseed_interval ( ) const

inlineinherited

Definition at line 128 of file stateful_rng.h.

{ return m_reseed_interval; }

Referenced by Botan::HMAC_DRBG::HMAC_DRBG().

security_level()

size_t Botan::ChaCha_RNG::security_level ( ) const

overridevirtual

Returns

intended security level of this DRBG

Implements Botan::Stateful_RNG.

Definition at line 82 of file chacha_rng.cpp.

   {
   return 256;
   }

---

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

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