src/random.h

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2016 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 #ifndef BITCOIN_RANDOM_H
   7 #define BITCOIN_RANDOM_H
   8
   9 #include "crypto/chacha20.h"
  10 #include "crypto/common.h"
  11 #include "uint256.h"
  12
  13 #include <stdint.h>
  14
  15 /* Seed OpenSSL PRNG with additional entropy data */
  16 void RandAddSeed();
  17
  18 /**
  19  * Functions to gather random data via the OpenSSL PRNG
  20  */
  21 void GetRandBytes(unsigned char* buf, int num);
  22 uint64_t GetRand(uint64_t nMax);
  23 int GetRandInt(int nMax);
  24 uint256 GetRandHash();
  25
  26 /**
  27  * Add a little bit of randomness to the output of GetStrongRangBytes.
  28  * This sleeps for a millisecond, so should only be called when there is
  29  * no other work to be done.
  30  */
  31 void RandAddSeedSleep();
  32
  33 /**
  34  * Function to gather random data from multiple sources, failing whenever any
  35  * of those source fail to provide a result.
  36  */
  37 void GetStrongRandBytes(unsigned char* buf, int num);
  38
  39 /**
  40  * Fast randomness source. This is seeded once with secure random data, but
  41  * is completely deterministic and insecure after that.
  42  * This class is not thread-safe.
  43  */
  44 class FastRandomContext {
  45 private:
  46     bool requires_seed;
  47     ChaCha20 rng;
  48
  49     unsigned char bytebuf[64];
  50     int bytebuf_size;
  51
  52     uint64_t bitbuf;
  53     int bitbuf_size;
  54
  55     void RandomSeed();
  56
  57     void FillByteBuffer()
  58     {
  59         if (requires_seed) {
  60             RandomSeed();
  61         }
  62         rng.Output(bytebuf, sizeof(bytebuf));
  63         bytebuf_size = sizeof(bytebuf);
  64     }
  65
  66     void FillBitBuffer()
  67     {
  68         bitbuf = rand64();
  69         bitbuf_size = 64;
  70     }
  71
  72 public:
  73     explicit FastRandomContext(bool fDeterministic = false);
  74
  75     /** Initialize with explicit seed (only for testing) */
  76     explicit FastRandomContext(const uint256& seed);
  77
  78     /** Generate a random 64-bit integer. */
  79     uint64_t rand64()
  80     {
  81         if (bytebuf_size < 8) FillByteBuffer();
  82         uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
  83         bytebuf_size -= 8;
  84         return ret;
  85     }
  86
  87     /** Generate a random (bits)-bit integer. */
  88     uint64_t randbits(int bits) {
  89         if (bits == 0) {
  90             return 0;
  91         } else if (bits > 32) {
  92             return rand64() >> (64 - bits);
  93         } else {
  94             if (bitbuf_size < bits) FillBitBuffer();
  95             uint64_t ret = bitbuf & (~(uint64_t)0 >> (64 - bits));
  96             bitbuf >>= bits;
  97             bitbuf_size -= bits;
  98             return ret;
  99         }
 100     }
 101
 102     /** Generate a random integer in the range [0..range). */
 103     uint64_t randrange(uint64_t range)
 104     {
 105         --range;
 106         int bits = CountBits(range);
 107         while (true) {
 108             uint64_t ret = randbits(bits);
 109             if (ret <= range) return ret;
 110         }
 111     }
 112
 113     /** Generate a random 32-bit integer. */
 114     uint32_t rand32() { return randbits(32); }
 115
 116     /** Generate a random boolean. */
 117     bool randbool() { return randbits(1); }
 118 };
 119
 120 /* Number of random bytes returned by GetOSRand.
 121  * When changing this constant make sure to change all call sites, and make
 122  * sure that the underlying OS APIs for all platforms support the number.
 123  * (many cap out at 256 bytes).
 124  */
 125 static const ssize_t NUM_OS_RANDOM_BYTES = 32;
 126
 127 /** Get 32 bytes of system entropy. Do not use this in application code: use
 128  * GetStrongRandBytes instead.
 129  */
 130 void GetOSRand(unsigned char *ent32);
 131
 132 /** Check that OS randomness is available and returning the requested number
 133  * of bytes.
 134  */
 135 bool Random_SanityCheck();
 136
 137 #endif // BITCOIN_RANDOM_H