random.cpp File Reference

#include "random.h"
#include "compat/cpuid.h"
#include "crypto/sha256.h"
#include "crypto/sha512.h"
#include "support/cleanse.h"
#include "support/allocators/secure.h"
#include "logging.h"
#include "sync.h"
#include "utiltime.h"
#include <stdlib.h>
#include <limits>
#include <chrono>
#include <thread>
#include "randomenv.h"
#include <fcntl.h>
#include <sys/time.h>

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Enumerations
enum class	RNGLevel { FAST , SLOW , PERIODIC }

Functions
void	GetDevURandom (unsigned char *ent32)
	Fallback: get 32 bytes of system entropy from /dev/urandom. More...
void	GetOSRand (unsigned char *ent32)
	Get 32 bytes of system entropy. More...
void	GetRandBytes (unsigned char *buf, int num) noexcept
	Overall design of the RNG and entropy sources. More...
void	GetStrongRandBytes (unsigned char *buf, int num) noexcept
	Gather entropy from various sources, feed it into the internal PRNG, and generate random data using it. More...
void	RandAddPeriodic () noexcept
	Gather entropy from various expensive sources, and feed them to the PRNG state. More...
void	RandAddEvent (const uint32_t event_info) noexcept
	Gathers entropy from the low bits of the time at which events occur. More...
uint64_t	GetRand (uint64_t nMax) noexcept
int	GetRandInt (int nMax) noexcept
uint256	GetRandHash () noexcept
bool	GetRandBool (double rate) noexcept
bool	Random_SanityCheck ()
	Check that OS randomness is available and returning the requested number of bytes. More...
void	RandomInit ()
	Initialize global RNG state and log any CPU features that are used. More...

Variables
bool	g_mock_deterministic_tests {false}
	Flag to make GetRand in random.h return the same number. More...

Enumeration Type Documentation

RNGLevel

enum RNGLevel

strong

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

Definition at line 544 of file random.cpp.

Function Documentation

GetDevURandom()

void GetDevURandom

(

unsigned char *

ent32

)

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 258 of file random.cpp.

GetOSRand()

void GetOSRand

(

unsigned char *

ent32

)

Get 32 bytes of system entropy.

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

Definition at line 278 of file random.cpp.

GetRand()

uint64_t GetRand ( uint64_t  nMax )

noexcept

Definition at line 586 of file random.cpp.

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GetRandBool()

bool GetRandBool ( double  rate )

noexcept

Definition at line 603 of file random.cpp.

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GetRandBytes()

void GetRandBytes ( unsigned char *  buf, int  num  )

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 579 of file random.cpp.

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GetRandHash()

uint256 GetRandHash ( )

noexcept

Definition at line 596 of file random.cpp.

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GetRandInt()

int GetRandInt ( int  nMax )

noexcept

Definition at line 591 of file random.cpp.

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GetStrongRandBytes()

void GetStrongRandBytes ( unsigned char *  buf, int  num  )

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 580 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 582 of file random.cpp.

RandAddPeriodic()

void RandAddPeriodic ( )

noexcept

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

Thread-safe.

Definition at line 581 of file random.cpp.

Random_SanityCheck()

bool Random_SanityCheck

(

)

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

Definition at line 647 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 716 of file random.cpp.

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Variable Documentation

g_mock_deterministic_tests

bool g_mock_deterministic_tests {false}

Flag to make GetRand in random.h return the same number.

Definition at line 584 of file random.cpp.