4fcfcc294e
On the ::SLOW path we would use OpenSSL as an additional source of random bytes. This commit removes that functionality. Note that this was always only an additional source, and that we never checked the return value RAND_bytes(): https://www.openssl.org/docs/manmaster/man3/RAND_bytes.html RAND_bytes() puts num cryptographically strong pseudo-random bytes into buf.
243 lines
8.2 KiB
C++
243 lines
8.2 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2018 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_RANDOM_H
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#define BITCOIN_RANDOM_H
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#include <crypto/chacha20.h>
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#include <crypto/common.h>
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#include <uint256.h>
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#include <chrono> // For std::chrono::microseconds
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#include <cstdint>
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#include <limits>
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/**
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* Overall design of the RNG and entropy sources.
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*
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* We maintain a single global 256-bit RNG state for all high-quality randomness.
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* The following (classes of) functions interact with that state by mixing in new
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* entropy, and optionally extracting random output from it:
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*
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* - The GetRand*() class of functions, as well as construction of FastRandomContext objects,
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* perform 'fast' seeding, consisting of mixing in:
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* - A stack pointer (indirectly committing to calling thread and call stack)
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* - A high-precision timestamp (rdtsc when available, c++ high_resolution_clock otherwise)
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* - 64 bits from the hardware RNG (rdrand) when available.
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* These entropy sources are very fast, and only designed to protect against situations
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* where a VM state restore/copy results in multiple systems with the same randomness.
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* FastRandomContext on the other hand does not protect against this once created, but
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* is even faster (and acceptable to use inside tight loops).
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*
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* - The GetStrongRand*() class of function perform 'slow' seeding, including everything
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* that fast seeding includes, but additionally:
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* - OS entropy (/dev/urandom, getrandom(), ...). The application will terminate if
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* this entropy source fails.
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* - Another high-precision timestamp (indirectly committing to a benchmark of all the
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* previous sources).
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* These entropy sources are slower, but designed to make sure the RNG state contains
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* fresh data that is unpredictable to attackers.
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*
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* - RandAddSeedSleep() seeds everything that fast seeding includes, but additionally:
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* - A high-precision timestamp before and after sleeping 1ms.
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* - (On Windows) Once every 10 minutes, performance monitoring data from the OS.
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- - Once every minute, strengthen the entropy for 10 ms using repeated SHA512.
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* These just exploit the fact the system is idle to improve the quality of the RNG
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* slightly.
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*
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* On first use of the RNG (regardless of what function is called first), all entropy
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* sources used in the 'slow' seeder are included, but also:
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* - 256 bits from the hardware RNG (rdseed or rdrand) when available.
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* - (On Windows) Performance monitoring data from the OS.
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* - Strengthen the entropy for 100 ms using repeated SHA512.
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*
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* When mixing in new entropy, H = SHA512(entropy || old_rng_state) is computed, and
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* (up to) the first 32 bytes of H are produced as output, while the last 32 bytes
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* become the new RNG state.
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*/
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/**
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* Generate random data via the internal PRNG.
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*
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* These functions are designed to be fast (sub microsecond), but do not necessarily
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* meaningfully add entropy to the PRNG state.
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*
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* Thread-safe.
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*/
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void GetRandBytes(unsigned char* buf, int num) noexcept;
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uint64_t GetRand(uint64_t nMax) noexcept;
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std::chrono::microseconds GetRandMicros(std::chrono::microseconds duration_max) noexcept;
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int GetRandInt(int nMax) noexcept;
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uint256 GetRandHash() noexcept;
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/**
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* Gather entropy from various sources, feed it into the internal PRNG, and
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* generate random data using it.
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*
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* This function will cause failure whenever the OS RNG fails.
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*
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* Thread-safe.
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*/
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void GetStrongRandBytes(unsigned char* buf, int num) noexcept;
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/**
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* Gather entropy from various expensive sources, and feed them to the PRNG state.
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*
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* Thread-safe.
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*/
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void RandAddPeriodic();
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/**
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* Fast randomness source. This is seeded once with secure random data, but
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* is completely deterministic and does not gather more entropy after that.
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*
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* This class is not thread-safe.
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*/
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class FastRandomContext {
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private:
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bool requires_seed;
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ChaCha20 rng;
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unsigned char bytebuf[64];
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int bytebuf_size;
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uint64_t bitbuf;
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int bitbuf_size;
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void RandomSeed();
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void FillByteBuffer()
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{
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if (requires_seed) {
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RandomSeed();
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}
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rng.Keystream(bytebuf, sizeof(bytebuf));
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bytebuf_size = sizeof(bytebuf);
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}
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void FillBitBuffer()
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{
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bitbuf = rand64();
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bitbuf_size = 64;
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}
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public:
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explicit FastRandomContext(bool fDeterministic = false) noexcept;
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/** Initialize with explicit seed (only for testing) */
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explicit FastRandomContext(const uint256& seed) noexcept;
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// Do not permit copying a FastRandomContext (move it, or create a new one to get reseeded).
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FastRandomContext(const FastRandomContext&) = delete;
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FastRandomContext(FastRandomContext&&) = delete;
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FastRandomContext& operator=(const FastRandomContext&) = delete;
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/** Move a FastRandomContext. If the original one is used again, it will be reseeded. */
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FastRandomContext& operator=(FastRandomContext&& from) noexcept;
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/** Generate a random 64-bit integer. */
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uint64_t rand64() noexcept
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{
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if (bytebuf_size < 8) FillByteBuffer();
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uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
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bytebuf_size -= 8;
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return ret;
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}
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/** Generate a random (bits)-bit integer. */
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uint64_t randbits(int bits) noexcept {
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if (bits == 0) {
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return 0;
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} else if (bits > 32) {
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return rand64() >> (64 - bits);
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} else {
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if (bitbuf_size < bits) FillBitBuffer();
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uint64_t ret = bitbuf & (~(uint64_t)0 >> (64 - bits));
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bitbuf >>= bits;
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bitbuf_size -= bits;
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return ret;
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}
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}
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/** Generate a random integer in the range [0..range). */
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uint64_t randrange(uint64_t range) noexcept
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{
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assert(range);
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--range;
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int bits = CountBits(range);
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while (true) {
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uint64_t ret = randbits(bits);
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if (ret <= range) return ret;
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}
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}
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/** Generate random bytes. */
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std::vector<unsigned char> randbytes(size_t len);
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/** Generate a random 32-bit integer. */
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uint32_t rand32() noexcept { return randbits(32); }
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/** generate a random uint256. */
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uint256 rand256() noexcept;
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/** Generate a random boolean. */
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bool randbool() noexcept { return randbits(1); }
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// Compatibility with the C++11 UniformRandomBitGenerator concept
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typedef uint64_t result_type;
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static constexpr uint64_t min() { return 0; }
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static constexpr uint64_t max() { return std::numeric_limits<uint64_t>::max(); }
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inline uint64_t operator()() noexcept { return rand64(); }
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};
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/** More efficient than using std::shuffle on a FastRandomContext.
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*
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* This is more efficient as std::shuffle will consume entropy in groups of
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* 64 bits at the time and throw away most.
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*
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* This also works around a bug in libstdc++ std::shuffle that may cause
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* type::operator=(type&&) to be invoked on itself, which the library's
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* debug mode detects and panics on. This is a known issue, see
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* https://stackoverflow.com/questions/22915325/avoiding-self-assignment-in-stdshuffle
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*/
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template<typename I, typename R>
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void Shuffle(I first, I last, R&& rng)
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{
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while (first != last) {
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size_t j = rng.randrange(last - first);
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if (j) {
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using std::swap;
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swap(*first, *(first + j));
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}
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++first;
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}
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}
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/* Number of random bytes returned by GetOSRand.
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* When changing this constant make sure to change all call sites, and make
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* sure that the underlying OS APIs for all platforms support the number.
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* (many cap out at 256 bytes).
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*/
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static const int NUM_OS_RANDOM_BYTES = 32;
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/** Get 32 bytes of system entropy. Do not use this in application code: use
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* GetStrongRandBytes instead.
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*/
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void GetOSRand(unsigned char *ent32);
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/** Check that OS randomness is available and returning the requested number
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* of bytes.
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*/
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bool Random_SanityCheck();
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/**
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* Initialize global RNG state and log any CPU features that are used.
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*
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* Calling this function is optional. RNG state will be initialized when first
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* needed if it is not called.
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*/
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void RandomInit();
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#endif // BITCOIN_RANDOM_H
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