Bitcoin Core  0.19.99
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Enumerations | Functions | Variables
random.cpp File Reference
#include <random.h>
#include <compat/cpuid.h>
#include <crypto/sha256.h>
#include <crypto/sha512.h>
#include <support/cleanse.h>
#include <logging.h>
#include <sync.h>
#include <util/time.h>
#include <stdlib.h>
#include <thread>
#include <randomenv.h>
#include <support/allocators/secure.h>
#include <fcntl.h>
#include <sys/time.h>
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Enumerations

enum  RNGLevel { RNGLevel::FAST, RNGLevel::SLOW, RNGLevel::PERIODIC }
 

Functions

static void RandFailure ()
 
static int64_t GetPerformanceCounter () noexcept
 
static void InitHardwareRand ()
 
static void ReportHardwareRand ()
 
static void SeedHardwareFast (CSHA512 &hasher) noexcept
 Add 64 bits of entropy gathered from hardware to hasher. More...
 
static void SeedHardwareSlow (CSHA512 &hasher) noexcept
 Add 256 bits of entropy gathered from hardware to hasher. More...
 
static void Strengthen (const unsigned char(&seed)[32], int microseconds, CSHA512 &hasher) noexcept
 Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher. More...
 
static 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...
 
static void SeedTimestamp (CSHA512 &hasher) noexcept
 
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. More...
 
static void SeedPeriodic (CSHA512 &hasher, RNGState &rng) noexcept
 
static void SeedStartup (CSHA512 &hasher, RNGState &rng) noexcept
 
static void ProcRand (unsigned char *out, int num, RNGLevel level) noexcept
 
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
 
std::chrono::microseconds GetRandMicros (std::chrono::microseconds duration_max) noexcept
 
int GetRandInt (int nMax) noexcept
 
uint256 GetRandHash () 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}
 

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 546 of file random.cpp.

Function Documentation

◆ GetDevURandom()

static void GetDevURandom ( unsigned char *  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 256 of file random.cpp.

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◆ GetOSRand()

void GetOSRand ( unsigned char *  ent32)

Get 32 bytes of system entropy.

Definition at line 276 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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◆ GetRand()

uint64_t GetRand ( uint64_t  nMax)
noexcept

Definition at line 588 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 581 of file random.cpp.

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◆ GetRandHash()

uint256 GetRandHash ( )
noexcept

Definition at line 603 of file random.cpp.

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◆ GetRandInt()

int GetRandInt ( int  nMax)
noexcept

Definition at line 598 of file random.cpp.

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◆ GetRandMicros()

std::chrono::microseconds GetRandMicros ( std::chrono::microseconds  duration_max)
noexcept

Definition at line 593 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 582 of file random.cpp.

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◆ InitHardwareRand()

static void InitHardwareRand ( )
static

Definition at line 184 of file random.cpp.

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◆ ProcRand()

static void ProcRand ( unsigned char *  out,
int  num,
RNGLevel  level 
)
staticnoexcept

Definition at line 552 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 584 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 583 of file random.cpp.

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◆ RandFailure()

static void RandFailure ( )
static

Definition at line 47 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.

Definition at line 643 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 712 of file random.cpp.

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◆ ReportHardwareRand()

static void ReportHardwareRand ( )
static

Definition at line 185 of file random.cpp.

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◆ SeedFast()

static void SeedFast ( CSHA512 hasher)
staticnoexcept

Definition at line 460 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 189 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 200 of file random.cpp.

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◆ SeedPeriodic()

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

Definition at line 506 of file random.cpp.

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◆ SeedSlow()

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

Definition at line 475 of file random.cpp.

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◆ SeedStartup()

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

Definition at line 526 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 497 of file random.cpp.

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◆ SeedTimestamp()

static void SeedTimestamp ( CSHA512 hasher)
staticnoexcept

Definition at line 454 of file random.cpp.

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◆ Strengthen()

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

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

Definition at line 225 of file random.cpp.

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Variable Documentation

◆ g_mock_deterministic_tests

bool g_mock_deterministic_tests {false}

Definition at line 586 of file random.cpp.