Line data    Source code

       1             : // Copyright (c) 2009-2010 Satoshi Nakamoto
       2             : // Copyright (c) 2009-2018 The Bitcoin developers
       3             : // Copyright (c) 2019-2021 The PIVX Core developers
       4             : // Distributed under the MIT/X11 software license, see the accompanying
       5             : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       6             : 
       7             : #ifndef PIVX_RANDOM_H
       8             : #define PIVX_RANDOM_H
       9             : 
      10             : #include "crypto/chacha20.h"
      11             : #include "crypto/common.h"
      12             : #include "uint256.h"
      13             : 
      14             : #include <stdint.h>
      15             : #include <limits>
      16             : 
      17             : /**
      18             :  * Overall design of the RNG and entropy sources.
      19             :  *
      20             :  * We maintain a single global 256-bit RNG state for all high-quality randomness.
      21             :  * The following (classes of) functions interact with that state by mixing in new
      22             :  * entropy, and optionally extracting random output from it:
      23             :  *
      24             :  * - The GetRand*() class of functions, as well as construction of FastRandomContext objects,
      25             :  *   perform 'fast' seeding, consisting of mixing in:
      26             :  *   - A stack pointer (indirectly committing to calling thread and call stack)
      27             :  *   - A high-precision timestamp (rdtsc when available, c++ high_resolution_clock otherwise)
      28             :  *   - 64 bits from the hardware RNG (rdrand) when available.
      29             :  *   These entropy sources are very fast, and only designed to protect against situations
      30             :  *   where a VM state restore/copy results in multiple systems with the same randomness.
      31             :  *   FastRandomContext on the other hand does not protect against this once created, but
      32             :  *   is even faster (and acceptable to use inside tight loops).
      33             :  *
      34             :  * - The GetStrongRand*() class of function perform 'slow' seeding, including everything
      35             :  *   that fast seeding includes, but additionally:
      36             :  *   - OS entropy (/dev/urandom, getrandom(), ...). The application will terminate if
      37             :  *     this entropy source fails.
      38             :  *   - Another high-precision timestamp (indirectly committing to a benchmark of all the
      39             :  *     previous sources).
      40             :  *   These entropy sources are slower, but designed to make sure the RNG state contains
      41             :  *   fresh data that is unpredictable to attackers.
      42             :  *
      43             :  * - RandAddPeriodic() seeds everything that fast seeding includes, but additionally:
      44             :  *   - A high-precision timestamp
      45             :  *   - Dynamic environment data (performance monitoring, ...)
      46             :  *   - Strengthen the entropy for 10 ms using repeated SHA512.
      47             :  *   This is run once every minute.
      48             :  *
      49             :  * On first use of the RNG (regardless of what function is called first), all entropy
      50             :  * sources used in the 'slow' seeder are included, but also:
      51             :  * - 256 bits from the hardware RNG (rdseed or rdrand) when available.
      52             :  * - Dynamic environment data (performance monitoring, ...)
      53             :  * - Static environment data
      54             :  * - Strengthen the entropy for 100 ms using repeated SHA512.
      55             :  *
      56             :  * When mixing in new entropy, H = SHA512(entropy || old_rng_state) is computed, and
      57             :  * (up to) the first 32 bytes of H are produced as output, while the last 32 bytes
      58             :  * become the new RNG state.
      59             : */
      60             : 
      61             : /**
      62             :  * Generate random data via the internal PRNG.
      63             :  *
      64             :  * These functions are designed to be fast (sub microsecond), but do not necessarily
      65             :  * meaningfully add entropy to the PRNG state.
      66             :  *
      67             :  * Thread-safe.
      68             :  */
      69             : void GetRandBytes(unsigned char* buf, int num) noexcept;
      70             : uint64_t GetRand(uint64_t nMax) noexcept;
      71             : int GetRandInt(int nMax) noexcept;
      72             : uint256 GetRandHash() noexcept;
      73             : 
      74             : bool GetRandBool(double rate) noexcept;
      75             : 
      76             : /**
      77             :  * Gather entropy from various sources, feed it into the internal PRNG, and
      78             :  * generate random data using it.
      79             :  *
      80             :  * This function will cause failure whenever the OS RNG fails.
      81             :  *
      82             :  * Thread-safe.
      83             :  */
      84             : void GetStrongRandBytes(unsigned char* buf, int num) noexcept;
      85             : 
      86             : /**
      87             :  * Gather entropy from various expensive sources, and feed them to the PRNG state.
      88             :  *
      89             :  * Thread-safe.
      90             :  */
      91             : void RandAddPeriodic() noexcept;
      92             : 
      93             : /**
      94             :  * Gathers entropy from the low bits of the time at which events occur. Should
      95             :  * be called with a uint32_t describing the event at the time an event occurs.
      96             :  *
      97             :  * Thread-safe.
      98             :  */
      99             : void RandAddEvent(const uint32_t event_info) noexcept;
     100             : 
     101             : /**
     102             :  * Fast randomness source. This is seeded once with secure random data, but
     103             :  * is completely deterministic and does not gather more entropy after that.
     104             :  *
     105             :  * This class is not thread-safe.
     106             :  */
     107             : class FastRandomContext {
     108             : private:
     109             :     bool requires_seed{false};
     110             :     ChaCha20 rng;
     111             : 
     112             :     unsigned char bytebuf[64];
     113             :     int bytebuf_size{0};
     114             : 
     115             :     uint64_t bitbuf{0};
     116             :     int bitbuf_size{0};
     117             : 
     118             :     void RandomSeed();
     119             : 
     120    14835931 :     void FillByteBuffer()
     121             :     {
     122    14835931 :         if (requires_seed) {
     123     2566073 :             RandomSeed();
     124             :         }
     125    14835931 :         rng.Keystream(bytebuf, sizeof(bytebuf));
     126    14835931 :         bytebuf_size = sizeof(bytebuf);
     127    14835931 :     }
     128             : 
     129    96493048 :     void FillBitBuffer()
     130             :     {
     131   192986516 :         bitbuf = rand64();
     132    96493048 :         bitbuf_size = 64;
     133    96493048 :     }
     134             : 
     135             : public:
     136             :     explicit FastRandomContext(bool fDeterministic = false) noexcept;
     137             : 
     138             :     /** Initialize with explicit seed (only for testing) */
     139             :     explicit FastRandomContext(const uint256& seed) noexcept;
     140             : 
     141             :     // Do not permit copying a FastRandomContext (move it, or create a new one to get reseeded).
     142             :     FastRandomContext(const FastRandomContext&) = delete;
     143             :     FastRandomContext(FastRandomContext&&) = delete;
     144             :     FastRandomContext& operator=(const FastRandomContext&) = delete;
     145             : 
     146             :     /** Move a FastRandomContext. If the original one is used again, it will be reseeded. */
     147             :     FastRandomContext& operator=(FastRandomContext&& from) noexcept;
     148             : 
     149             :     /** Generate a random 64-bit integer. */
     150    99083130 :     uint64_t rand64() noexcept
     151             :     {
     152    98991508 :         if (bytebuf_size < 8) FillByteBuffer();
     153     2590069 :         uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
     154    99083130 :         bytebuf_size -= 8;
     155    98984846 :         return ret;
     156             :     }
     157             : 
     158             :     /** Generate a random (bits)-bit integer. */
     159  1023910481 :     uint64_t randbits(int bits) noexcept {
     160  1023910481 :         if (bits == 0) {
     161             :             return 0;
     162  1023839608 :         } else if (bits > 32) {
     163     5087808 :             return rand64() >> (64 - bits);
     164             :         } else {
     165  1021250165 :             if (bitbuf_size < bits) FillBitBuffer();
     166  1021250165 :             uint64_t ret = bitbuf & (~(uint64_t)0 >> (64 - bits));
     167  1021250165 :             bitbuf >>= bits;
     168  1021250165 :             bitbuf_size -= bits;
     169  1021250165 :             return ret;
     170             :         }
     171             :     }
     172             : 
     173             :     /** Generate a random integer in the range [0..range). */
     174     4644056 :     uint64_t randrange(uint64_t range) noexcept
     175             :     {
     176     7774986 :         --range;
     177     7524588 :         int bits = CountBits(range);
     178     8634507 :         while (true) {
     179     8634507 :             uint64_t ret = randbits(bits);
     180     8634507 :             if (ret <= range) return ret;
     181             :         }
     182             :     }
     183             : 
     184             :     /** Generate random bytes. */
     185             :     std::vector<unsigned char> randbytes(size_t len);
     186             : 
     187             :     /** Generate a random 16-bit integer. */
     188           2 :     uint16_t rand16() { return randbits(16); }
     189             : 
     190             :     /** Generate a random 32-bit integer. */
     191    16890456 :     uint32_t rand32() noexcept { return randbits(32); }
     192             : 
     193             :     /** generate a random uint256. */
     194             :     uint256 rand256() noexcept;
     195             : 
     196             :     /** Generate a random boolean. */
     197   343722702 :     bool randbool() noexcept { return randbits(1); }
     198             : 
     199             :     // Compatibility with the C++11 UniformRandomBitGenerator concept
     200             :     typedef uint64_t result_type;
     201             :     static constexpr uint64_t min() { return 0; }
     202             :     static constexpr uint64_t max() { return std::numeric_limits<uint64_t>::max(); }
     203         674 :     inline uint64_t operator()() noexcept { return rand64(); }
     204             : };
     205             : 
     206             : /** More efficient than using std::shuffle on a FastRandomContext.
     207             :  *
     208             :  * This is more efficient as std::shuffle will consume entropy in groups of
     209             :  * 64 bits at the time and throw away most.
     210             :  *
     211             :  * This also works around a bug in libstdc++ std::shuffle that may cause
     212             :  * type::operator=(type&&) to be invoked on itself, which the library's
     213             :  * debug mode detects and panics on. This is a known issue, see
     214             :  * https://stackoverflow.com/questions/22915325/avoiding-self-assignment-in-stdshuffle
     215             :  */
     216             : template<typename I, typename R>
     217       46299 : void Shuffle(I first, I last, R&& rng)
     218             : {
     219     1058151 :     while (first != last) {
     220     1011852 :         size_t j = rng.randrange(last - first);
     221     1011852 :         if (j) {
     222             :             using std::swap;
     223      905930 :             swap(*first, *(first + j));
     224             :         }
     225     1046151 :         ++first;
     226             :     }
     227       46299 : }
     228             : 
     229             : /* Number of random bytes returned by GetOSRand.
     230             :  * When changing this constant make sure to change all call sites, and make
     231             :  * sure that the underlying OS APIs for all platforms support the number.
     232             :  * (many cap out at 256 bytes).
     233             :  */
     234             : static const ssize_t NUM_OS_RANDOM_BYTES = 32;
     235             : 
     236             : /** Get 32 bytes of system entropy. Do not use this in application code: use
     237             :  * GetStrongRandBytes instead.
     238             :  */
     239             : void GetOSRand(unsigned char *ent32);
     240             : 
     241             : /** Check that OS randomness is available and returning the requested number
     242             :  * of bytes.
     243             :  */
     244             : bool Random_SanityCheck();
     245             : 
     246             : /**
     247             :  * Initialize global RNG state and log any CPU features that are used.
     248             :  *
     249             :  * Calling this function is optional. RNG state will be initialized when first
     250             :  * needed if it is not called.
     251             :  */
     252             : void RandomInit();
     253             : 
     254             : #endif // PIVX_RANDOM_H