random.cpp File Reference

#include <random.h>
#include <compat/cpuid.h>
#include <crypto/sha256.h>
#include <crypto/sha512.h>
#include <logging.h>
#include <randomenv.h>
#include <span.h>
#include <support/allocators/secure.h>
#include <support/cleanse.h>
#include <sync.h>
#include <util/time.h>
#include <cmath>
#include <cstdlib>
#include <memory>
#include <thread>
#include <fcntl.h>
#include <sys/time.h>

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Enumerations
enum class	RNGLevel { FAST , SLOW , PERIODIC }

Functions
static void	RandFailure ()
static int64_t	GetPerformanceCounter () noexcept
static void	InitHardwareRand ()
	Access to other hardware random number generators could be added here later, assuming it is sufficiently fast (in the order of a few hundred CPU cycles).
static void	ReportHardwareRand ()
static void	SeedHardwareFast (CSHA512 &hasher) noexcept
	Add 64 bits of entropy gathered from hardware to hasher.
static void	SeedHardwareSlow (CSHA512 &hasher) noexcept
	Add 256 bits of entropy gathered from hardware to hasher.
static void	Strengthen (const uint8_t(&seed)[32], int microseconds, CSHA512 &hasher) noexcept
	Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher.
static void	GetDevURandom (uint8_t *ent32)
	Fallback: get 32 bytes of system entropy from /dev/urandom.
void	GetOSRand (uint8_t *ent32)
	Get 32 bytes of system entropy.
static void	SeedTimestamp (CSHA512 &hasher) noexcept
	A note on the use of noexcept in the seeding functions below:
static void	SeedFast (CSHA512 &hasher) noexcept
static void	SeedSlow (CSHA512 &hasher, RNGState &rng) noexcept
static void	SeedStrengthen (CSHA512 &hasher, RNGState &rng, int microseconds) noexcept
	Extract entropy from rng, strengthen it, and feed it into hasher.
static void	SeedPeriodic (CSHA512 &hasher, RNGState &rng) noexcept
static void	SeedStartup (CSHA512 &hasher, RNGState &rng) noexcept
static void	ProcRand (uint8_t *out, int num, RNGLevel level) noexcept
void	GetRandBytes (Span< uint8_t > bytes) noexcept
	Overall design of the RNG and entropy sources.
void	GetStrongRandBytes (Span< uint8_t > bytes) noexcept
	Gather entropy from various sources, feed it into the internal PRNG, and generate random data using it.
void	RandAddPeriodic () noexcept
	Gather entropy from various expensive sources, and feed them to the PRNG state.
void	RandAddEvent (const uint32_t event_info) noexcept
	Gathers entropy from the low bits of the time at which events occur.
uint64_t	GetRandInternal (uint64_t nMax) noexcept
	Generate a uniform random integer in the range [0..range).
uint256	GetRandHash () noexcept
bool	Random_SanityCheck ()
	Check that OS randomness is available and returning the requested number of bytes.
void	RandomInit ()
	Initialize global RNG state and log any CPU features that are used.
std::chrono::microseconds	GetExponentialRand (std::chrono::microseconds now, std::chrono::seconds average_interval)
	Return a timestamp in the future sampled from an exponential distribution (https://en.wikipedia.org/wiki/Exponential_distribution).

Variables
bool	g_mock_deterministic_tests {false}

Enumeration Type Documentation

RNGLevel

enum class RNGLevel

strong

Enumerator
FAST	Automatically called by GetRandBytes.
SLOW	Automatically called by GetStrongRandBytes.
PERIODIC	Called by RandAddPeriodic()

Definition at line 604 of file random.cpp.

Function Documentation

GetDevURandom()

static void GetDevURandom ( uint8_t *  ent32 )

static

Fallback: get 32 bytes of system entropy from /dev/urandom.

The most compatible way to get cryptographic randomness on UNIX-ish platforms.

Definition at line 300 of file random.cpp.

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GetExponentialRand()

std::chrono::microseconds GetExponentialRand	(	std::chrono::microseconds	now,
		std::chrono::seconds	average_interval
	)

Return a timestamp in the future sampled from an exponential distribution (https://en.wikipedia.org/wiki/Exponential_distribution).

This distribution is memoryless and should be used for repeated network events (e.g. sending a certain type of message) to minimize leaking information to observers.

The probability of an event occuring before time x is 1 - e^-(x/a) where a is the average interval between events.

Definition at line 794 of file random.cpp.

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GetOSRand()

void GetOSRand

(

uint8_t *

ent32

)

Get 32 bytes of system entropy.

Do not use this in application code: use GetStrongRandBytes instead.

Fall back to /dev/urandom if there is no specific method implemented to get system entropy for this OS.

Definition at line 319 of file random.cpp.

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GetPerformanceCounter()

static int64_t GetPerformanceCounter ( )

inlinestaticnoexcept

Definition at line 53 of file random.cpp.

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GetRandBytes()

void GetRandBytes ( Span< uint8_t >  bytes )

noexcept

Overall design of the RNG and entropy sources.

We maintain a single global 256-bit RNG state for all high-quality randomness. The following (classes of) functions interact with that state by mixing in new entropy, and optionally extracting random output from it:

• The GetRand*() class of functions, as well as construction of FastRandomContext objects, perform 'fast' seeding, consisting of mixing in:
  • A stack pointer (indirectly committing to calling thread and call stack)
  • A high-precision timestamp (rdtsc when available, c++ high_resolution_clock otherwise)
  • 64 bits from the hardware RNG (rdrand) when available. These entropy sources are very fast, and only designed to protect against situations where a VM state restore/copy results in multiple systems with the same randomness. FastRandomContext on the other hand does not protect against this once created, but is even faster (and acceptable to use inside tight loops).
• The GetStrongRand*() class of function perform 'slow' seeding, including everything that fast seeding includes, but additionally:
  • OS entropy (/dev/urandom, getrandom(), ...). The application will terminate if this entropy source fails.
  • Another high-precision timestamp (indirectly committing to a benchmark of all the previous sources). These entropy sources are slower, but designed to make sure the RNG state contains fresh data that is unpredictable to attackers.
• RandAddPeriodic() seeds everything that fast seeding includes, but additionally:
  • A high-precision timestamp
  • Dynamic environment data (performance monitoring, ...)
  • Strengthen the entropy for 10 ms using repeated SHA512. This is run once every minute.

On first use of the RNG (regardless of what function is called first), all entropy sources used in the 'slow' seeder are included, but also:

• 256 bits from the hardware RNG (rdseed or rdrand) when available.
• Dynamic environment data (performance monitoring, ...)
• Static environment data
• Strengthen the entropy for 100 ms using repeated SHA512.

When mixing in new entropy, H = SHA512(entropy || old_rng_state) is computed, and (up to) the first 32 bytes of H are produced as output, while the last 32 bytes become the new RNG state. Generate random data via the internal PRNG.

These functions are designed to be fast (sub microsecond), but do not necessarily meaningfully add entropy to the PRNG state.

Thread-safe.

Definition at line 639 of file random.cpp.

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GetRandHash()

uint256 GetRandHash ( )

noexcept

Definition at line 659 of file random.cpp.

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GetRandInternal()

uint64_t GetRandInternal ( uint64_t  nMax )

noexcept

Generate a uniform random integer in the range [0..range).

Precondition: range > 0

Definition at line 655 of file random.cpp.

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GetStrongRandBytes()

void GetStrongRandBytes ( Span< uint8_t >  bytes )

noexcept

Gather entropy from various sources, feed it into the internal PRNG, and generate random data using it.

This function will cause failure whenever the OS RNG fails.

Thread-safe.

Definition at line 642 of file random.cpp.

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InitHardwareRand()

static void InitHardwareRand ( )

static

Access to other hardware random number generators could be added here later, assuming it is sufficiently fast (in the order of a few hundred CPU cycles).

Slower sources should probably be invoked separately, and/or only from RandAddPeriodic (which is called once a minute).

Definition at line 216 of file random.cpp.

ProcRand()

static void ProcRand ( uint8_t *  out, int  num, RNGLevel  level  )

staticnoexcept

Definition at line 610 of file random.cpp.

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RandAddEvent()

void RandAddEvent ( const uint32_t  event_info )

noexcept

Gathers entropy from the low bits of the time at which events occur.

Should be called with a uint32_t describing the event at the time an event occurs.

Thread-safe.

Definition at line 649 of file random.cpp.

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RandAddPeriodic()

void RandAddPeriodic ( )

noexcept

Gather entropy from various expensive sources, and feed them to the PRNG state.

Thread-safe.

Definition at line 645 of file random.cpp.

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RandFailure()

static void RandFailure ( )

static

Definition at line 48 of file random.cpp.

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Random_SanityCheck()

bool Random_SanityCheck

(

)

Check that OS randomness is available and returning the requested number of bytes.

This does not measure the quality of randomness, but it does test that GetOSRand() overwrites all 32 bytes of the output given a maximum number of tries.

Loop until all bytes have been overwritten at least once, or max number tries reached.

Definition at line 706 of file random.cpp.

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RandomInit()

void RandomInit

(

)

Initialize global RNG state and log any CPU features that are used.

Calling this function is optional. RNG state will be initialized when first needed if it is not called.

Definition at line 786 of file random.cpp.

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ReportHardwareRand()

static void ReportHardwareRand ( )

static

Definition at line 217 of file random.cpp.

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SeedFast()

static void SeedFast ( CSHA512 &  hasher )

staticnoexcept

Definition at line 516 of file random.cpp.

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SeedHardwareFast()

static void SeedHardwareFast ( CSHA512 &  hasher )

staticnoexcept

Add 64 bits of entropy gathered from hardware to hasher.

Do nothing if not supported.

Definition at line 224 of file random.cpp.

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SeedHardwareSlow()

static void SeedHardwareSlow ( CSHA512 &  hasher )

staticnoexcept

Add 256 bits of entropy gathered from hardware to hasher.

Do nothing if not supported.

Definition at line 238 of file random.cpp.

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SeedPeriodic()

static void SeedPeriodic ( CSHA512 &  hasher, RNGState &  rng  )

staticnoexcept

Definition at line 563 of file random.cpp.

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SeedSlow()

static void SeedSlow ( CSHA512 &  hasher, RNGState &  rng  )

staticnoexcept

Definition at line 530 of file random.cpp.

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SeedStartup()

static void SeedStartup ( CSHA512 &  hasher, RNGState &  rng  )

staticnoexcept

Definition at line 584 of file random.cpp.

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SeedStrengthen()

static void SeedStrengthen ( CSHA512 &  hasher, RNGState &  rng, int  microseconds  )

staticnoexcept

Extract entropy from rng, strengthen it, and feed it into hasher.

Definition at line 552 of file random.cpp.

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SeedTimestamp()

static void SeedTimestamp ( CSHA512 &  hasher )

staticnoexcept

A note on the use of noexcept in the seeding functions below:

None of the RNG code should ever throw any exception.

Definition at line 511 of file random.cpp.

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Strengthen()

static void Strengthen ( const uint8_t(&)  seed[32], int  microseconds, CSHA512 &  hasher  )

staticnoexcept

Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher.

Definition at line 268 of file random.cpp.

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Variable Documentation

g_mock_deterministic_tests

bool g_mock_deterministic_tests {false}

Definition at line 653 of file random.cpp.