1 // Copyright (c) 2009-2010 Satoshi Nakamoto
2 // Copyright (c) 2009-present The Bitcoin Core developers
3 // Distributed under the MIT software license, see the accompanying
4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
5 6 #include <bitcoin-build-config.h> // IWYU pragma: keep
7 8 #include <random.h>
9 10 #include <compat/compat.h>
11 #include <compat/cpuid.h>
12 #include <crypto/chacha20.h>
13 #include <crypto/sha256.h>
14 #include <crypto/sha512.h>
15 #include <randomenv.h>
16 #include <span.h>
17 #include <support/allocators/secure.h>
18 #include <support/cleanse.h>
19 #include <sync.h>
20 #include <util/log.h>
21 #include <util/time.h>
22 23 #include <array>
24 #include <cmath>
25 #include <cstdlib>
26 #include <optional>
27 #include <thread>
28 29 #ifdef WIN32
30 #include <bcrypt.h>
31 #else
32 #include <fcntl.h>
33 #include <sys/time.h>
34 #endif
35 36 #if defined(HAVE_GETRANDOM) || (defined(HAVE_GETENTROPY_RAND) && defined(__APPLE__))
37 #include <sys/random.h>
38 #endif
39 40 #ifdef HAVE_SYSCTL_ARND
41 #include <sys/sysctl.h>
42 #endif
43 44 namespace {
45 46 /* Number of random bytes returned by GetOSRand.
47 * When changing this constant make sure to change all call sites, and make
48 * sure that the underlying OS APIs for all platforms support the number.
49 * (many cap out at 256 bytes).
50 */
51 static const int NUM_OS_RANDOM_BYTES = 32;
52 53 54 [[noreturn]] void RandFailure()
55 {
56 LogError("Failed to read randomness, aborting\n");
57 std::abort();
58 }
59 60 inline int64_t GetPerformanceCounter() noexcept
61 {
62 // Read the hardware time stamp counter when available.
63 // See https://en.wikipedia.org/wiki/Time_Stamp_Counter for more information.
64 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
65 return __rdtsc();
66 #elif !defined(_MSC_VER) && defined(__i386__)
67 uint64_t r = 0;
68 __asm__ volatile ("rdtsc" : "=A"(r)); // Constrain the r variable to the eax:edx pair.
69 return r;
70 #elif !defined(_MSC_VER) && (defined(__x86_64__) || defined(__amd64__))
71 uint64_t r1 = 0, r2 = 0;
72 __asm__ volatile ("rdtsc" : "=a"(r1), "=d"(r2)); // Constrain r1 to rax and r2 to rdx.
73 return (r2 << 32) | r1;
74 #else
75 // Fall back to using standard library clock (usually microsecond or nanosecond precision)
76 return std::chrono::high_resolution_clock::now().time_since_epoch().count();
77 #endif
78 }
79 80 #ifdef HAVE_GETCPUID
81 bool g_rdrand_supported = false;
82 bool g_rdseed_supported = false;
83 constexpr uint32_t CPUID_F1_ECX_RDRAND = 0x40000000;
84 constexpr uint32_t CPUID_F7_EBX_RDSEED = 0x00040000;
85 #ifdef bit_RDRND
86 static_assert(CPUID_F1_ECX_RDRAND == bit_RDRND, "Unexpected value for bit_RDRND");
87 #endif
88 #ifdef bit_RDSEED
89 static_assert(CPUID_F7_EBX_RDSEED == bit_RDSEED, "Unexpected value for bit_RDSEED");
90 #endif
91 92 void InitHardwareRand()
93 {
94 uint32_t eax, ebx, ecx, edx;
95 GetCPUID(1, 0, eax, ebx, ecx, edx);
96 if (ecx & CPUID_F1_ECX_RDRAND) {
97 g_rdrand_supported = true;
98 }
99 GetCPUID(7, 0, eax, ebx, ecx, edx);
100 if (ebx & CPUID_F7_EBX_RDSEED) {
101 g_rdseed_supported = true;
102 }
103 }
104 105 void ReportHardwareRand()
106 {
107 // This must be done in a separate function, as InitHardwareRand() may be indirectly called
108 // from global constructors, before logging is initialized.
109 if (g_rdseed_supported) {
110 LogInfo("Using RdSeed as an additional entropy source");
111 }
112 if (g_rdrand_supported) {
113 LogInfo("Using RdRand as an additional entropy source");
114 }
115 }
116 117 /** Read 64 bits of entropy using rdrand.
118 *
119 * Must only be called when RdRand is supported.
120 */
121 uint64_t GetRdRand() noexcept
122 {
123 // RdRand may very rarely fail. Invoke it up to 10 times in a loop to reduce this risk.
124 #ifdef __i386__
125 uint8_t ok = 0;
126 // Initialize to 0 to silence a compiler warning that r1 or r2 may be used
127 // uninitialized. Even if rdrand fails (!ok) it will set the output to 0,
128 // but there is no way that the compiler could know that.
129 uint32_t r1 = 0, r2 = 0;
130 for (int i = 0; i < 10; ++i) {
131 __asm__ volatile (".byte 0x0f, 0xc7, 0xf0; setc %1" : "=a"(r1), "=q"(ok) :: "cc"); // rdrand %eax
132 if (ok) break;
133 }
134 for (int i = 0; i < 10; ++i) {
135 __asm__ volatile (".byte 0x0f, 0xc7, 0xf0; setc %1" : "=a"(r2), "=q"(ok) :: "cc"); // rdrand %eax
136 if (ok) break;
137 }
138 return (((uint64_t)r2) << 32) | r1;
139 #elif defined(__x86_64__) || defined(__amd64__)
140 uint8_t ok = 0;
141 uint64_t r1 = 0; // See above why we initialize to 0.
142 for (int i = 0; i < 10; ++i) {
143 __asm__ volatile (".byte 0x48, 0x0f, 0xc7, 0xf0; setc %1" : "=a"(r1), "=q"(ok) :: "cc"); // rdrand %rax
144 if (ok) break;
145 }
146 return r1;
147 #else
148 #error "RdRand is only supported on x86 and x86_64"
149 #endif
150 }
151 152 /** Read 64 bits of entropy using rdseed.
153 *
154 * Must only be called when RdSeed is supported.
155 */
156 uint64_t GetRdSeed() noexcept
157 {
158 // RdSeed may fail when the HW RNG is overloaded. Loop indefinitely until enough entropy is gathered,
159 // but pause after every failure.
160 #ifdef __i386__
161 uint8_t ok = 0;
162 uint32_t r1, r2;
163 do {
164 __asm__ volatile (".byte 0x0f, 0xc7, 0xf8; setc %1" : "=a"(r1), "=q"(ok) :: "cc"); // rdseed %eax
165 if (ok) break;
166 __asm__ volatile ("pause");
167 } while(true);
168 do {
169 __asm__ volatile (".byte 0x0f, 0xc7, 0xf8; setc %1" : "=a"(r2), "=q"(ok) :: "cc"); // rdseed %eax
170 if (ok) break;
171 __asm__ volatile ("pause");
172 } while(true);
173 return (((uint64_t)r2) << 32) | r1;
174 #elif defined(__x86_64__) || defined(__amd64__)
175 uint8_t ok;
176 uint64_t r1;
177 do {
178 __asm__ volatile (".byte 0x48, 0x0f, 0xc7, 0xf8; setc %1" : "=a"(r1), "=q"(ok) :: "cc"); // rdseed %rax
179 if (ok) break;
180 __asm__ volatile ("pause");
181 } while(true);
182 return r1;
183 #else
184 #error "RdSeed is only supported on x86 and x86_64"
185 #endif
186 }
187 188 #else
189 /* Access to other hardware random number generators could be added here later,
190 * assuming it is sufficiently fast (in the order of a few hundred CPU cycles).
191 * Slower sources should probably be invoked separately, and/or only from
192 * RandAddPeriodic (which is called once a minute).
193 */
194 void InitHardwareRand() {}
195 void ReportHardwareRand() {}
196 #endif
197 198 /** Add 64 bits of entropy gathered from hardware to hasher. Do nothing if not supported. */
199 void SeedHardwareFast(CSHA512& hasher) noexcept {
200 #if defined(__x86_64__) || defined(__amd64__) || defined(__i386__)
201 if (g_rdrand_supported) {
202 uint64_t out = GetRdRand();
203 hasher.Write((const unsigned char*)&out, sizeof(out));
204 return;
205 }
206 #endif
207 }
208 209 /** Add 256 bits of entropy gathered from hardware to hasher. Do nothing if not supported. */
210 void SeedHardwareSlow(CSHA512& hasher) noexcept {
211 #if defined(__x86_64__) || defined(__amd64__) || defined(__i386__)
212 // When we want 256 bits of entropy, prefer RdSeed over RdRand, as it's
213 // guaranteed to produce independent randomness on every call.
214 if (g_rdseed_supported) {
215 for (int i = 0; i < 4; ++i) {
216 uint64_t out = GetRdSeed();
217 hasher.Write((const unsigned char*)&out, sizeof(out));
218 }
219 return;
220 }
221 // When falling back to RdRand, XOR the result of 1024 results.
222 // This guarantees a reseeding occurs between each.
223 if (g_rdrand_supported) {
224 for (int i = 0; i < 4; ++i) {
225 uint64_t out = 0;
226 for (int j = 0; j < 1024; ++j) out ^= GetRdRand();
227 hasher.Write((const unsigned char*)&out, sizeof(out));
228 }
229 return;
230 }
231 #endif
232 }
233 234 /** Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher. */
235 void Strengthen(const unsigned char (&seed)[32], SteadyClock::duration dur, CSHA512& hasher) noexcept
236 {
237 CSHA512 inner_hasher;
238 inner_hasher.Write(seed, sizeof(seed));
239 240 // Hash loop
241 unsigned char buffer[64];
242 const auto stop{SteadyClock::now() + dur};
243 do {
244 for (int i = 0; i < 1000; ++i) {
245 inner_hasher.Finalize(buffer);
246 inner_hasher.Reset();
247 inner_hasher.Write(buffer, sizeof(buffer));
248 }
249 // Benchmark operation and feed it into outer hasher.
250 int64_t perf = GetPerformanceCounter();
251 hasher.Write((const unsigned char*)&perf, sizeof(perf));
252 } while (SteadyClock::now() < stop);
253 254 // Produce output from inner state and feed it to outer hasher.
255 inner_hasher.Finalize(buffer);
256 hasher.Write(buffer, sizeof(buffer));
257 // Try to clean up.
258 inner_hasher.Reset();
259 memory_cleanse(buffer, sizeof(buffer));
260 }
261 262 #ifndef WIN32
263 /** Fallback: get 32 bytes of system entropy from /dev/urandom. The most
264 * compatible way to get cryptographic randomness on UNIX-ish platforms.
265 */
266 [[maybe_unused]] void GetDevURandom(unsigned char *ent32)
267 {
268 int f = open("/dev/urandom", O_RDONLY);
269 if (f == -1) {
270 RandFailure();
271 }
272 int have = 0;
273 do {
274 ssize_t n = read(f, ent32 + have, NUM_OS_RANDOM_BYTES - have);
275 if (n <= 0 || n + have > NUM_OS_RANDOM_BYTES) {
276 close(f);
277 RandFailure();
278 }
279 have += n;
280 } while (have < NUM_OS_RANDOM_BYTES);
281 close(f);
282 }
283 #endif
284 285 /** Get 32 bytes of system entropy. */
286 void GetOSRand(unsigned char *ent32)
287 {
288 #if defined(WIN32)
289 constexpr uint32_t STATUS_SUCCESS{0x00000000};
290 NTSTATUS status = BCryptGenRandom(/*hAlgorithm=*/NULL,
291 /*pbBuffer=*/ent32,
292 /*cbBuffer=*/NUM_OS_RANDOM_BYTES,
293 /*dwFlags=*/BCRYPT_USE_SYSTEM_PREFERRED_RNG);
294 295 if (status != STATUS_SUCCESS) {
296 RandFailure();
297 }
298 #elif defined(HAVE_GETRANDOM)
299 /* Linux. From the getrandom(2) man page:
300 * "If the urandom source has been initialized, reads of up to 256 bytes
301 * will always return as many bytes as requested and will not be
302 * interrupted by signals."
303 */
304 if (getrandom(ent32, NUM_OS_RANDOM_BYTES, 0) != NUM_OS_RANDOM_BYTES) {
305 RandFailure();
306 }
307 #elif defined(__OpenBSD__)
308 /* OpenBSD. From the arc4random(3) man page:
309 "Use of these functions is encouraged for almost all random number
310 consumption because the other interfaces are deficient in either
311 quality, portability, standardization, or availability."
312 The function call is always successful.
313 */
314 arc4random_buf(ent32, NUM_OS_RANDOM_BYTES);
315 #elif defined(HAVE_GETENTROPY_RAND) && defined(__APPLE__)
316 if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
317 RandFailure();
318 }
319 #elif defined(HAVE_SYSCTL_ARND)
320 /* FreeBSD, NetBSD and similar. It is possible for the call to return less
321 * bytes than requested, so need to read in a loop.
322 */
323 static int name[2] = {CTL_KERN, KERN_ARND};
324 int have = 0;
325 do {
326 size_t len = NUM_OS_RANDOM_BYTES - have;
327 if (sysctl(name, std::size(name), ent32 + have, &len, nullptr, 0) != 0) {
328 RandFailure();
329 }
330 have += len;
331 } while (have < NUM_OS_RANDOM_BYTES);
332 #else
333 /* Fall back to /dev/urandom if there is no specific method implemented to
334 * get system entropy for this OS.
335 */
336 GetDevURandom(ent32);
337 #endif
338 }
339 340 class RNGState {
341 Mutex m_mutex;
342 /* The RNG state consists of 256 bits of entropy, taken from the output of
343 * one operation's SHA512 output, and fed as input to the next one.
344 * Carrying 256 bits of entropy should be sufficient to guarantee
345 * unpredictability as long as any entropy source was ever unpredictable
346 * to an attacker. To protect against situations where an attacker might
347 * observe the RNG's state, fresh entropy is always mixed when
348 * GetStrongRandBytes is called.
349 */
350 unsigned char m_state[32] GUARDED_BY(m_mutex) = {0};
351 uint64_t m_counter GUARDED_BY(m_mutex) = 0;
352 bool m_strongly_seeded GUARDED_BY(m_mutex) = false;
353 354 /** If not nullopt, the output of this RNGState is redirected and drawn from here
355 * (unless always_use_real_rng is passed to MixExtract). */
356 std::optional<ChaCha20> m_deterministic_prng GUARDED_BY(m_mutex);
357 358 Mutex m_events_mutex;
359 CSHA256 m_events_hasher GUARDED_BY(m_events_mutex);
360 361 public:
362 RNGState() noexcept
363 {
364 InitHardwareRand();
365 }
366 367 ~RNGState() = default;
368 369 void AddEvent(uint32_t event_info) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_events_mutex)
370 {
371 LOCK(m_events_mutex);
372 373 m_events_hasher.Write((const unsigned char *)&event_info, sizeof(event_info));
374 // Get the low four bytes of the performance counter. This translates to roughly the
375 // subsecond part.
376 uint32_t perfcounter = (GetPerformanceCounter() & 0xffffffff);
377 m_events_hasher.Write((const unsigned char*)&perfcounter, sizeof(perfcounter));
378 }
379 380 /**
381 * Feed (the hash of) all events added through AddEvent() to hasher.
382 */
383 void SeedEvents(CSHA512& hasher) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_events_mutex)
384 {
385 // We use only SHA256 for the events hashing to get the ASM speedups we have for SHA256,
386 // since we want it to be fast as network peers may be able to trigger it repeatedly.
387 LOCK(m_events_mutex);
388 389 unsigned char events_hash[32];
390 m_events_hasher.Finalize(events_hash);
391 hasher.Write(events_hash, 32);
392 393 // Re-initialize the hasher with the finalized state to use later.
394 m_events_hasher.Reset();
395 m_events_hasher.Write(events_hash, 32);
396 }
397 398 /** Make the output of MixExtract (unless always_use_real_rng) deterministic, with specified seed. */
399 void MakeDeterministic(const uint256& seed) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
400 {
401 LOCK(m_mutex);
402 m_deterministic_prng.emplace(MakeByteSpan(seed));
403 }
404 405 /** Extract up to 32 bytes of entropy from the RNG state, mixing in new entropy from hasher.
406 *
407 * If this function has never been called with strong_seed = true, false is returned.
408 *
409 * If always_use_real_rng is false, and MakeDeterministic has been called before, output
410 * from the deterministic PRNG instead.
411 */
412 bool MixExtract(unsigned char* out, size_t num, CSHA512&& hasher, bool strong_seed, bool always_use_real_rng) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
413 {
414 assert(num <= 32);
415 unsigned char buf[64];
416 static_assert(sizeof(buf) == CSHA512::OUTPUT_SIZE, "Buffer needs to have hasher's output size");
417 bool ret;
418 {
419 LOCK(m_mutex);
420 ret = (m_strongly_seeded |= strong_seed);
421 // Write the current state of the RNG into the hasher
422 hasher.Write(m_state, 32);
423 // Write a new counter number into the state
424 hasher.Write((const unsigned char*)&m_counter, sizeof(m_counter));
425 ++m_counter;
426 // Finalize the hasher
427 hasher.Finalize(buf);
428 // Store the last 32 bytes of the hash output as new RNG state.
429 memcpy(m_state, buf + 32, 32);
430 // Handle requests for deterministic randomness.
431 if (!always_use_real_rng && m_deterministic_prng.has_value()) [[unlikely]] {
432 // Overwrite the beginning of buf, which will be used for output.
433 m_deterministic_prng->Keystream(std::as_writable_bytes(std::span{buf, num}));
434 // Do not require strong seeding for deterministic output.
435 ret = true;
436 }
437 }
438 // If desired, copy (up to) the first 32 bytes of the hash output as output.
439 if (num) {
440 assert(out != nullptr);
441 memcpy(out, buf, num);
442 }
443 // Best effort cleanup of internal state
444 hasher.Reset();
445 memory_cleanse(buf, 64);
446 return ret;
447 }
448 };
449 450 RNGState& GetRNGState() noexcept
451 {
452 // This idiom relies on the guarantee that static variable are initialized
453 // on first call, even when multiple parallel calls are permitted.
454 static std::vector<RNGState, secure_allocator<RNGState>> g_rng(1);
455 return g_rng[0];
456 }
457 458 /* A note on the use of noexcept in the seeding functions below:
459 *
460 * None of the RNG code should ever throw any exception.
461 */
462 463 void SeedTimestamp(CSHA512& hasher) noexcept
464 {
465 int64_t perfcounter = GetPerformanceCounter();
466 hasher.Write((const unsigned char*)&perfcounter, sizeof(perfcounter));
467 }
468 469 void SeedFast(CSHA512& hasher) noexcept
470 {
471 unsigned char buffer[32];
472 473 // Stack pointer to indirectly commit to thread/callstack
474 const unsigned char* ptr = buffer;
475 hasher.Write((const unsigned char*)&ptr, sizeof(ptr));
476 477 // Hardware randomness is very fast when available; use it always.
478 SeedHardwareFast(hasher);
479 480 // High-precision timestamp
481 SeedTimestamp(hasher);
482 }
483 484 void SeedSlow(CSHA512& hasher, RNGState& rng) noexcept
485 {
486 unsigned char buffer[32];
487 488 // Everything that the 'fast' seeder includes
489 SeedFast(hasher);
490 491 // OS randomness
492 GetOSRand(buffer);
493 hasher.Write(buffer, sizeof(buffer));
494 495 // Add the events hasher into the mix
496 rng.SeedEvents(hasher);
497 498 // High-precision timestamp.
499 //
500 // Note that we also commit to a timestamp in the Fast seeder, so we indirectly commit to a
501 // benchmark of all the entropy gathering sources in this function).
502 SeedTimestamp(hasher);
503 }
504 505 /** Extract entropy from rng, strengthen it, and feed it into hasher. */
506 void SeedStrengthen(CSHA512& hasher, RNGState& rng, SteadyClock::duration dur) noexcept
507 {
508 // Generate 32 bytes of entropy from the RNG, and a copy of the entropy already in hasher.
509 // Never use the deterministic PRNG for this, as the result is only used internally.
510 unsigned char strengthen_seed[32];
511 rng.MixExtract(strengthen_seed, sizeof(strengthen_seed), CSHA512(hasher), false, /*always_use_real_rng=*/true);
512 // Strengthen the seed, and feed it into hasher.
513 Strengthen(strengthen_seed, dur, hasher);
514 }
515 516 void SeedPeriodic(CSHA512& hasher, RNGState& rng) noexcept
517 {
518 // Everything that the 'fast' seeder includes
519 SeedFast(hasher);
520 521 // High-precision timestamp
522 SeedTimestamp(hasher);
523 524 // Add the events hasher into the mix
525 rng.SeedEvents(hasher);
526 527 // Dynamic environment data (clocks, resource usage, ...)
528 auto old_size = hasher.Size();
529 RandAddDynamicEnv(hasher);
530 LogDebug(BCLog::RAND, "Feeding %i bytes of dynamic environment data into RNG\n", hasher.Size() - old_size);
531 532 // Strengthen for 10 ms
533 SeedStrengthen(hasher, rng, 10ms);
534 }
535 536 void SeedStartup(CSHA512& hasher, RNGState& rng) noexcept
537 {
538 // Gather 256 bits of hardware randomness, if available
539 SeedHardwareSlow(hasher);
540 541 // Everything that the 'slow' seeder includes.
542 SeedSlow(hasher, rng);
543 544 // Dynamic environment data (clocks, resource usage, ...)
545 auto old_size = hasher.Size();
546 RandAddDynamicEnv(hasher);
547 548 // Static environment data
549 RandAddStaticEnv(hasher);
550 LogDebug(BCLog::RAND, "Feeding %i bytes of environment data into RNG\n", hasher.Size() - old_size);
551 552 // Strengthen for 100 ms
553 SeedStrengthen(hasher, rng, 100ms);
554 }
555 556 enum class RNGLevel {
557 FAST, //!< Automatically called by GetRandBytes
558 SLOW, //!< Automatically called by GetStrongRandBytes
559 PERIODIC, //!< Called by RandAddPeriodic()
560 };
561 562 void ProcRand(unsigned char* out, int num, RNGLevel level, bool always_use_real_rng) noexcept
563 {
564 // Make sure the RNG is initialized first (as all Seed* function possibly need hwrand to be available).
565 RNGState& rng = GetRNGState();
566 567 assert(num <= 32);
568 569 CSHA512 hasher;
570 switch (level) {
571 case RNGLevel::FAST:
572 SeedFast(hasher);
573 break;
574 case RNGLevel::SLOW:
575 SeedSlow(hasher, rng);
576 break;
577 case RNGLevel::PERIODIC:
578 SeedPeriodic(hasher, rng);
579 break;
580 }
581 582 // Combine with and update state
583 if (!rng.MixExtract(out, num, std::move(hasher), false, always_use_real_rng)) {
584 // On the first invocation, also seed with SeedStartup().
585 CSHA512 startup_hasher;
586 SeedStartup(startup_hasher, rng);
587 rng.MixExtract(out, num, std::move(startup_hasher), true, always_use_real_rng);
588 }
589 }
590 591 } // namespace
592 593 594 /** Internal function to set g_determinstic_rng. Only accessed from tests. */
595 void MakeRandDeterministicDANGEROUS(const uint256& seed) noexcept
596 {
597 GetRNGState().MakeDeterministic(seed);
598 }
599 std::atomic<bool> g_used_g_prng{false}; // Only accessed from tests
600 601 void GetRandBytes(std::span<unsigned char> bytes) noexcept
602 {
603 g_used_g_prng = true;
604 ProcRand(bytes.data(), bytes.size(), RNGLevel::FAST, /*always_use_real_rng=*/false);
605 }
606 607 void GetStrongRandBytes(std::span<unsigned char> bytes) noexcept
608 {
609 ProcRand(bytes.data(), bytes.size(), RNGLevel::SLOW, /*always_use_real_rng=*/true);
610 }
611 612 void RandAddPeriodic() noexcept
613 {
614 ProcRand(nullptr, 0, RNGLevel::PERIODIC, /*always_use_real_rng=*/false);
615 }
616 617 void RandAddEvent(const uint32_t event_info) noexcept { GetRNGState().AddEvent(event_info); }
618 619 void FastRandomContext::RandomSeed() noexcept
620 {
621 uint256 seed = GetRandHash();
622 rng.SetKey(MakeByteSpan(seed));
623 requires_seed = false;
624 }
625 626 void FastRandomContext::fillrand(std::span<std::byte> output) noexcept
627 {
628 if (requires_seed) RandomSeed();
629 rng.Keystream(output);
630 }
631 632 FastRandomContext::FastRandomContext(const uint256& seed) noexcept : requires_seed(false), rng(MakeByteSpan(seed)) {}
633 634 void FastRandomContext::Reseed(const uint256& seed) noexcept
635 {
636 FlushCache();
637 requires_seed = false;
638 rng = {MakeByteSpan(seed)};
639 }
640 641 bool Random_SanityCheck()
642 {
643 uint64_t start = GetPerformanceCounter();
644 645 /* This does not measure the quality of randomness, but it does test that
646 * GetOSRand() overwrites all 32 bytes of the output given a maximum
647 * number of tries.
648 */
649 static constexpr int MAX_TRIES{1024};
650 uint8_t data[NUM_OS_RANDOM_BYTES];
651 bool overwritten[NUM_OS_RANDOM_BYTES] = {}; /* Tracks which bytes have been overwritten at least once */
652 int num_overwritten;
653 int tries = 0;
654 /* Loop until all bytes have been overwritten at least once, or max number tries reached */
655 do {
656 memset(data, 0, NUM_OS_RANDOM_BYTES);
657 GetOSRand(data);
658 for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
659 overwritten[x] |= (data[x] != 0);
660 }
661 662 num_overwritten = 0;
663 for (int x=0; x < NUM_OS_RANDOM_BYTES; ++x) {
664 if (overwritten[x]) {
665 num_overwritten += 1;
666 }
667 }
668 669 tries += 1;
670 } while (num_overwritten < NUM_OS_RANDOM_BYTES && tries < MAX_TRIES);
671 if (num_overwritten != NUM_OS_RANDOM_BYTES) return false; /* If this failed, bailed out after too many tries */
672 673 // Check that GetPerformanceCounter increases at least during a GetOSRand() call + 1ms sleep.
674 std::this_thread::sleep_for(std::chrono::milliseconds(1));
675 uint64_t stop = GetPerformanceCounter();
676 if (stop == start) return false;
677 678 // We called GetPerformanceCounter. Use it as entropy.
679 CSHA512 to_add;
680 to_add.Write((const unsigned char*)&start, sizeof(start));
681 to_add.Write((const unsigned char*)&stop, sizeof(stop));
682 GetRNGState().MixExtract(nullptr, 0, std::move(to_add), false, /*always_use_real_rng=*/true);
683 684 return true;
685 }
686 687 static constexpr std::array<std::byte, ChaCha20::KEYLEN> ZERO_KEY{};
688 689 FastRandomContext::FastRandomContext(bool fDeterministic) noexcept : requires_seed(!fDeterministic), rng(ZERO_KEY)
690 {
691 // Note that despite always initializing with ZERO_KEY, requires_seed is set to true if not
692 // fDeterministic. That means the rng will be reinitialized with a secure random key upon first
693 // use.
694 }
695 696 void RandomInit()
697 {
698 // Invoke RNG code to trigger initialization (if not already performed)
699 ProcRand(nullptr, 0, RNGLevel::FAST, /*always_use_real_rng=*/true);
700 701 ReportHardwareRand();
702 }
703 704 double MakeExponentiallyDistributed(uint64_t uniform) noexcept
705 {
706 // To convert uniform into an exponentially-distributed double, we use two steps:
707 // - Convert uniform into a uniformly-distributed double in range [0, 1), use the expression
708 // ((uniform >> 11) * 0x1.0p-53), as described in https://prng.di.unimi.it/ under
709 // "Generating uniform doubles in the unit interval". Call this value x.
710 // - Given an x in uniformly distributed in [0, 1), we find an exponentially distributed value
711 // by applying the quantile function to it. For the exponential distribution with mean 1 this
712 // is F(x) = -log(1 - x).
713 //
714 // Combining the two, and using log1p(x) = log(1 + x), we obtain the following:
715 return -std::log1p((uniform >> 11) * -0x1.0p-53);
716 }
717