From c21cbe61c6249bcfca098705df6f9b4baab9f296 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Fri, 17 Feb 2017 16:32:16 -0800
Subject: [PATCH 1/5] Introduce FastRandomContext::randbool()

---
 src/random.h          | 4 ++++
 src/wallet/wallet.cpp | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/random.h b/src/random.h
index 0464bdce1..82886bec5 100644
--- a/src/random.h
+++ b/src/random.h
@@ -42,6 +42,10 @@ public:
         return (Rw << 16) + Rz;
     }
 
+    bool randbool() {
+        return rand32() & 1;
+    }
+
     uint32_t Rz;
     uint32_t Rw;
 };
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 39e2ab7c1..2f9d47aa0 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -2048,7 +2048,7 @@ static void ApproximateBestSubset(const std::vector<std::pair<CAmount, std::pair
                 //that the rng is fast. We do not use a constant random sequence,
                 //because there may be some privacy improvement by making
                 //the selection random.
-                if (nPass == 0 ? insecure_rand.rand32()&1 : !vfIncluded[i])
+                if (nPass == 0 ? insecure_rand.randbool() : !vfIncluded[i])
                 {
                     nTotal += vValue[i].first;
                     vfIncluded[i] = true;

From 663fbae7776b0c238f6f27d73811b4bc627d0b6b Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 15 Feb 2017 17:56:54 -0800
Subject: [PATCH 2/5] FastRandom benchmark

---
 src/bench/crypto_hash.cpp | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/bench/crypto_hash.cpp b/src/bench/crypto_hash.cpp
index 737d3572a..5257e60e8 100644
--- a/src/bench/crypto_hash.cpp
+++ b/src/bench/crypto_hash.cpp
@@ -7,6 +7,7 @@
 #include "bench.h"
 #include "bloom.h"
 #include "hash.h"
+#include "random.h"
 #include "uint256.h"
 #include "utiltime.h"
 #include "crypto/ripemd160.h"
@@ -69,6 +70,28 @@ static void SipHash_32b(benchmark::State& state)
     }
 }
 
+static void FastRandom_32bit(benchmark::State& state)
+{
+    FastRandomContext rng(true);
+    uint32_t x;
+    while (state.KeepRunning()) {
+        for (int i = 0; i < 1000000; i++) {
+            x += rng.rand32();
+        }
+    }
+}
+
+static void FastRandom_1bit(benchmark::State& state)
+{
+    FastRandomContext rng(true);
+    uint32_t x;
+    while (state.KeepRunning()) {
+        for (int i = 0; i < 1000000; i++) {
+            x += rng.randbool();
+        }
+    }
+}
+
 BENCHMARK(RIPEMD160);
 BENCHMARK(SHA1);
 BENCHMARK(SHA256);
@@ -76,3 +99,5 @@ BENCHMARK(SHA512);
 
 BENCHMARK(SHA256_32b);
 BENCHMARK(SipHash_32b);
+BENCHMARK(FastRandom_32bit);
+BENCHMARK(FastRandom_1bit);

From e04326fe6652543dc26d90eba4a48fbdc935fd0c Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 15 Feb 2017 12:29:23 -0800
Subject: [PATCH 3/5] Add ChaCha20

---
 src/Makefile.am           |   2 +
 src/crypto/chacha20.cpp   | 180 ++++++++++++++++++++++++++++++++++++++
 src/crypto/chacha20.h     |  26 ++++++
 src/test/crypto_tests.cpp |  45 ++++++++++
 4 files changed, 253 insertions(+)
 create mode 100644 src/crypto/chacha20.cpp
 create mode 100644 src/crypto/chacha20.h

diff --git a/src/Makefile.am b/src/Makefile.am
index 8a3215688..89dd4c8f7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -242,6 +242,8 @@ crypto_libbitcoin_crypto_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 crypto_libbitcoin_crypto_a_SOURCES = \
   crypto/aes.cpp \
   crypto/aes.h \
+  crypto/chacha20.h \
+  crypto/chacha20.cpp \
   crypto/common.h \
   crypto/hmac_sha256.cpp \
   crypto/hmac_sha256.h \
diff --git a/src/crypto/chacha20.cpp b/src/crypto/chacha20.cpp
new file mode 100644
index 000000000..816ae870e
--- /dev/null
+++ b/src/crypto/chacha20.cpp
@@ -0,0 +1,180 @@
+// Copyright (c) 2017 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+// Based on the public domain implementation 'merged' by D. J. Bernstein
+// See https://cr.yp.to/chacha.html.
+
+#include "crypto/common.h"
+#include "crypto/chacha20.h"
+
+#include <string.h>
+
+constexpr static inline uint32_t rotl32(uint32_t v, int c) { return (v << c) | (v >> (32 - c)); }
+
+#define QUARTERROUND(a,b,c,d) \
+  a += b; d = rotl32(d ^ a, 16); \
+  c += d; b = rotl32(b ^ c, 12); \
+  a += b; d = rotl32(d ^ a, 8); \
+  c += d; b = rotl32(b ^ c, 7);
+
+static const unsigned char sigma[] = "expand 32-byte k";
+static const unsigned char tau[] = "expand 16-byte k";
+
+void ChaCha20::SetKey(const unsigned char* k, size_t keylen)
+{
+    const unsigned char *constants;
+
+    input[4] = ReadLE32(k + 0);
+    input[5] = ReadLE32(k + 4);
+    input[6] = ReadLE32(k + 8);
+    input[7] = ReadLE32(k + 12);
+    if (keylen == 32) { /* recommended */
+        k += 16;
+        constants = sigma;
+    } else { /* keylen == 16 */
+        constants = tau;
+    }
+    input[8] = ReadLE32(k + 0);
+    input[9] = ReadLE32(k + 4);
+    input[10] = ReadLE32(k + 8);
+    input[11] = ReadLE32(k + 12);
+    input[0] = ReadLE32(constants + 0);
+    input[1] = ReadLE32(constants + 4);
+    input[2] = ReadLE32(constants + 8);
+    input[3] = ReadLE32(constants + 12);
+    input[12] = 0;
+    input[13] = 0;
+    input[14] = 0;
+    input[15] = 0;
+}
+
+ChaCha20::ChaCha20()
+{
+    memset(input, 0, sizeof(input));
+}
+
+ChaCha20::ChaCha20(const unsigned char* k, size_t keylen)
+{
+    SetKey(k, keylen);
+}
+
+void ChaCha20::SetIV(uint64_t iv)
+{
+    input[14] = iv;
+    input[15] = iv >> 32;
+}
+
+void ChaCha20::Seek(uint64_t pos)
+{
+    input[12] = pos;
+    input[13] = pos >> 32;
+}
+
+void ChaCha20::Output(unsigned char* c, size_t bytes)
+{
+    uint32_t x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
+    uint32_t j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
+    unsigned char *ctarget = NULL;
+    unsigned char tmp[64];
+    unsigned int i;
+
+    if (!bytes) return;
+
+    j0 = input[0];
+    j1 = input[1];
+    j2 = input[2];
+    j3 = input[3];
+    j4 = input[4];
+    j5 = input[5];
+    j6 = input[6];
+    j7 = input[7];
+    j8 = input[8];
+    j9 = input[9];
+    j10 = input[10];
+    j11 = input[11];
+    j12 = input[12];
+    j13 = input[13];
+    j14 = input[14];
+    j15 = input[15];
+
+    for (;;) {
+        if (bytes < 64) {
+            ctarget = c;
+            c = tmp;
+        }
+        x0 = j0;
+        x1 = j1;
+        x2 = j2;
+        x3 = j3;
+        x4 = j4;
+        x5 = j5;
+        x6 = j6;
+        x7 = j7;
+        x8 = j8;
+        x9 = j9;
+        x10 = j10;
+        x11 = j11;
+        x12 = j12;
+        x13 = j13;
+        x14 = j14;
+        x15 = j15;
+        for (i = 20;i > 0;i -= 2) {
+            QUARTERROUND( x0, x4, x8,x12)
+            QUARTERROUND( x1, x5, x9,x13)
+            QUARTERROUND( x2, x6,x10,x14)
+            QUARTERROUND( x3, x7,x11,x15)
+            QUARTERROUND( x0, x5,x10,x15)
+            QUARTERROUND( x1, x6,x11,x12)
+            QUARTERROUND( x2, x7, x8,x13)
+            QUARTERROUND( x3, x4, x9,x14)
+        }
+        x0 += j0;
+        x1 += j1;
+        x2 += j2;
+        x3 += j3;
+        x4 += j4;
+        x5 += j5;
+        x6 += j6;
+        x7 += j7;
+        x8 += j8;
+        x9 += j9;
+        x10 += j10;
+        x11 += j11;
+        x12 += j12;
+        x13 += j13;
+        x14 += j14;
+        x15 += j15;
+
+        ++j12;
+        if (!j12) ++j13;
+
+        WriteLE32(c + 0, x0);
+        WriteLE32(c + 4, x1);
+        WriteLE32(c + 8, x2);
+        WriteLE32(c + 12, x3);
+        WriteLE32(c + 16, x4);
+        WriteLE32(c + 20, x5);
+        WriteLE32(c + 24, x6);
+        WriteLE32(c + 28, x7);
+        WriteLE32(c + 32, x8);
+        WriteLE32(c + 36, x9);
+        WriteLE32(c + 40, x10);
+        WriteLE32(c + 44, x11);
+        WriteLE32(c + 48, x12);
+        WriteLE32(c + 52, x13);
+        WriteLE32(c + 56, x14);
+        WriteLE32(c + 60, x15);
+
+        if (bytes <= 64) {
+            if (bytes < 64) {
+                for (i = 0;i < bytes;++i) ctarget[i] = c[i];
+            }
+            input[12] = j12;
+            input[13] = j13;
+            return;
+        }
+        bytes -= 64;
+        c += 64;
+    }
+}
diff --git a/src/crypto/chacha20.h b/src/crypto/chacha20.h
new file mode 100644
index 000000000..a305977bc
--- /dev/null
+++ b/src/crypto/chacha20.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2017 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_CRYPTO_CHACHA20_H
+#define BITCOIN_CRYPTO_CHACHA20_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+/** A PRNG class for ChaCha20. */
+class ChaCha20
+{
+private:
+    uint32_t input[16];
+
+public:
+    ChaCha20();
+    ChaCha20(const unsigned char* key, size_t keylen);
+    void SetKey(const unsigned char* key, size_t keylen);
+    void SetIV(uint64_t iv);
+    void Seek(uint64_t pos);
+    void Output(unsigned char* output, size_t bytes);
+};
+
+#endif // BITCOIN_CRYPTO_CHACHA20_H
diff --git a/src/test/crypto_tests.cpp b/src/test/crypto_tests.cpp
index 4d1741717..a20182afb 100644
--- a/src/test/crypto_tests.cpp
+++ b/src/test/crypto_tests.cpp
@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "crypto/aes.h"
+#include "crypto/chacha20.h"
 #include "crypto/ripemd160.h"
 #include "crypto/sha1.h"
 #include "crypto/sha256.h"
@@ -187,6 +188,19 @@ void TestAES256CBC(const std::string &hexkey, const std::string &hexiv, bool pad
     }
 }
 
+void TestChaCha20(const std::string &hexkey, uint64_t nonce, uint64_t seek, const std::string& hexout)
+{
+    std::vector<unsigned char> key = ParseHex(hexkey);
+    ChaCha20 rng(key.data(), key.size());
+    rng.SetIV(nonce);
+    rng.Seek(seek);
+    std::vector<unsigned char> out = ParseHex(hexout);
+    std::vector<unsigned char> outres;
+    outres.resize(out.size());
+    rng.Output(outres.data(), outres.size());
+    BOOST_CHECK(out == outres);
+}
+
 std::string LongTestString(void) {
     std::string ret;
     for (int i=0; i<200000; i++) {
@@ -439,4 +453,35 @@ BOOST_AUTO_TEST_CASE(aes_cbc_testvectors) {
                   "b2eb05e2c39be9fcda6c19078c6a9d1b3f461796d6b0d6b2e0c2a72b4d80e644");
 }
 
+
+BOOST_AUTO_TEST_CASE(chacha20_testvector)
+{
+    // Test vector from RFC 7539
+    TestChaCha20("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f", 0x4a000000UL, 1,
+                 "224f51f3401bd9e12fde276fb8631ded8c131f823d2c06e27e4fcaec9ef3cf788a3b0aa372600a92b57974cded2b9334794cb"
+                 "a40c63e34cdea212c4cf07d41b769a6749f3f630f4122cafe28ec4dc47e26d4346d70b98c73f3e9c53ac40c5945398b6eda1a"
+                 "832c89c167eacd901d7e2bf363");
+
+    // Test vectors from https://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-04#section-7
+    TestChaCha20("0000000000000000000000000000000000000000000000000000000000000000", 0, 0,
+                 "76b8e0ada0f13d90405d6ae55386bd28bdd219b8a08ded1aa836efcc8b770dc7da41597c5157488d7724e03fb8d84a376a43b"
+                 "8f41518a11cc387b669b2ee6586");
+    TestChaCha20("0000000000000000000000000000000000000000000000000000000000000001", 0, 0,
+                 "4540f05a9f1fb296d7736e7b208e3c96eb4fe1834688d2604f450952ed432d41bbe2a0b6ea7566d2a5d1e7e20d42af2c53d79"
+                 "2b1c43fea817e9ad275ae546963");
+    TestChaCha20("0000000000000000000000000000000000000000000000000000000000000000", 0x0100000000000000ULL, 0,
+                 "de9cba7bf3d69ef5e786dc63973f653a0b49e015adbff7134fcb7df137821031e85a050278a7084527214f73efc7fa5b52770"
+                 "62eb7a0433e445f41e3");
+    TestChaCha20("0000000000000000000000000000000000000000000000000000000000000000", 1, 0,
+                 "ef3fdfd6c61578fbf5cf35bd3dd33b8009631634d21e42ac33960bd138e50d32111e4caf237ee53ca8ad6426194a88545ddc4"
+                 "97a0b466e7d6bbdb0041b2f586b");
+    TestChaCha20("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f", 0x0706050403020100ULL, 0,
+                 "f798a189f195e66982105ffb640bb7757f579da31602fc93ec01ac56f85ac3c134a4547b733b46413042c9440049176905d3b"
+                 "e59ea1c53f15916155c2be8241a38008b9a26bc35941e2444177c8ade6689de95264986d95889fb60e84629c9bd9a5acb1cc1"
+                 "18be563eb9b3a4a472f82e09a7e778492b562ef7130e88dfe031c79db9d4f7c7a899151b9a475032b63fc385245fe054e3dd5"
+                 "a97a5f576fe064025d3ce042c566ab2c507b138db853e3d6959660996546cc9c4a6eafdc777c040d70eaf46f76dad3979e5c5"
+                 "360c3317166a1c894c94a371876a94df7628fe4eaaf2ccb27d5aaae0ad7ad0f9d4b6ad3b54098746d4524d38407a6deb3ab78"
+                 "fab78c9");
+}
+
 BOOST_AUTO_TEST_SUITE_END()

From 16329224e70d0525208f6b0ba00c5e1531a4f5ea Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 15 Feb 2017 17:45:22 -0800
Subject: [PATCH 4/5] Switch FastRandomContext to ChaCha20

---
 src/Makefile.test.include    |  2 +-
 src/addrman.cpp              |  8 ++---
 src/addrman.h                | 11 ++++--
 src/random.cpp               | 33 ++++++++++--------
 src/random.h                 | 66 +++++++++++++++++++++++++++++++-----
 src/test/addrman_tests.cpp   |  9 ++---
 src/test/prevector_tests.cpp |  8 ++---
 src/test/random_tests.cpp    | 21 +++++++++++-
 src/test/test_bitcoin.cpp    |  3 +-
 src/test/test_random.h       |  8 ++++-
 10 files changed, 126 insertions(+), 43 deletions(-)

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index fe0ed59fe..194fc0c24 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -57,8 +57,8 @@ BITCOIN_TESTS =\
   test/policyestimator_tests.cpp \
   test/pow_tests.cpp \
   test/prevector_tests.cpp \
-  test/random_tests.cpp \
   test/raii_event_tests.cpp \
+  test/random_tests.cpp \
   test/reverselock_tests.cpp \
   test/rpc_tests.cpp \
   test/sanity_tests.cpp \
diff --git a/src/addrman.cpp b/src/addrman.cpp
index b6ab4c630..33a623c1f 100644
--- a/src/addrman.cpp
+++ b/src/addrman.cpp
@@ -351,8 +351,8 @@ CAddrInfo CAddrMan::Select_(bool newOnly)
             int nKBucket = RandomInt(ADDRMAN_TRIED_BUCKET_COUNT);
             int nKBucketPos = RandomInt(ADDRMAN_BUCKET_SIZE);
             while (vvTried[nKBucket][nKBucketPos] == -1) {
-                nKBucket = (nKBucket + insecure_rand.rand32()) % ADDRMAN_TRIED_BUCKET_COUNT;
-                nKBucketPos = (nKBucketPos + insecure_rand.rand32()) % ADDRMAN_BUCKET_SIZE;
+                nKBucket = (nKBucket + insecure_rand.randbits(ADDRMAN_TRIED_BUCKET_COUNT_LOG2)) % ADDRMAN_TRIED_BUCKET_COUNT;
+                nKBucketPos = (nKBucketPos + insecure_rand.randbits(ADDRMAN_BUCKET_SIZE_LOG2)) % ADDRMAN_BUCKET_SIZE;
             }
             int nId = vvTried[nKBucket][nKBucketPos];
             assert(mapInfo.count(nId) == 1);
@@ -368,8 +368,8 @@ CAddrInfo CAddrMan::Select_(bool newOnly)
             int nUBucket = RandomInt(ADDRMAN_NEW_BUCKET_COUNT);
             int nUBucketPos = RandomInt(ADDRMAN_BUCKET_SIZE);
             while (vvNew[nUBucket][nUBucketPos] == -1) {
-                nUBucket = (nUBucket + insecure_rand.rand32()) % ADDRMAN_NEW_BUCKET_COUNT;
-                nUBucketPos = (nUBucketPos + insecure_rand.rand32()) % ADDRMAN_BUCKET_SIZE;
+                nUBucket = (nUBucket + insecure_rand.randbits(ADDRMAN_NEW_BUCKET_COUNT_LOG2)) % ADDRMAN_NEW_BUCKET_COUNT;
+                nUBucketPos = (nUBucketPos + insecure_rand.randbits(ADDRMAN_BUCKET_SIZE_LOG2)) % ADDRMAN_BUCKET_SIZE;
             }
             int nId = vvNew[nUBucket][nUBucketPos];
             assert(mapInfo.count(nId) == 1);
diff --git a/src/addrman.h b/src/addrman.h
index 6e5f946bf..bb45ac91e 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -136,13 +136,13 @@ public:
  */
 
 //! total number of buckets for tried addresses
-#define ADDRMAN_TRIED_BUCKET_COUNT 256
+#define ADDRMAN_TRIED_BUCKET_COUNT_LOG2 8
 
 //! total number of buckets for new addresses
-#define ADDRMAN_NEW_BUCKET_COUNT 1024
+#define ADDRMAN_NEW_BUCKET_COUNT_LOG2 10
 
 //! maximum allowed number of entries in buckets for new and tried addresses
-#define ADDRMAN_BUCKET_SIZE 64
+#define ADDRMAN_BUCKET_SIZE_LOG2 6
 
 //! over how many buckets entries with tried addresses from a single group (/16 for IPv4) are spread
 #define ADDRMAN_TRIED_BUCKETS_PER_GROUP 8
@@ -171,6 +171,11 @@ public:
 //! the maximum number of nodes to return in a getaddr call
 #define ADDRMAN_GETADDR_MAX 2500
 
+//! Convenience
+#define ADDRMAN_TRIED_BUCKET_COUNT (1 << ADDRMAN_TRIED_BUCKET_COUNT_LOG2)
+#define ADDRMAN_NEW_BUCKET_COUNT (1 << ADDRMAN_NEW_BUCKET_COUNT_LOG2)
+#define ADDRMAN_BUCKET_SIZE (1 << ADDRMAN_BUCKET_SIZE_LOG2)
+
 /** 
  * Stochastical (IP) address manager 
  */
diff --git a/src/random.cpp b/src/random.cpp
index 8284f457c..c1e313cbd 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -240,22 +240,16 @@ uint256 GetRandHash()
     return hash;
 }
 
-FastRandomContext::FastRandomContext(bool fDeterministic)
+void FastRandomContext::RandomSeed()
 {
-    // The seed values have some unlikely fixed points which we avoid.
-    if (fDeterministic) {
-        Rz = Rw = 11;
-    } else {
-        uint32_t tmp;
-        do {
-            GetRandBytes((unsigned char*)&tmp, 4);
-        } while (tmp == 0 || tmp == 0x9068ffffU);
-        Rz = tmp;
-        do {
-            GetRandBytes((unsigned char*)&tmp, 4);
-        } while (tmp == 0 || tmp == 0x464fffffU);
-        Rw = tmp;
-    }
+    uint256 seed = GetRandHash();
+    rng.SetKey(seed.begin(), 32);
+    requires_seed = false;
+}
+
+FastRandomContext::FastRandomContext(const uint256& seed) : requires_seed(false), bytebuf_size(0), bitbuf_size(0)
+{
+    rng.SetKey(seed.begin(), 32);
 }
 
 bool Random_SanityCheck()
@@ -288,3 +282,12 @@ bool Random_SanityCheck()
     } while (num_overwritten < NUM_OS_RANDOM_BYTES && tries < MAX_TRIES);
     return (num_overwritten == NUM_OS_RANDOM_BYTES); /* If this failed, bailed out after too many tries */
 }
+
+FastRandomContext::FastRandomContext(bool fDeterministic) : requires_seed(!fDeterministic), bytebuf_size(0), bitbuf_size(0)
+{
+    if (!fDeterministic) {
+        return;
+    }
+    uint256 seed;
+    rng.SetKey(seed.begin(), 32);
+}
diff --git a/src/random.h b/src/random.h
index 82886bec5..077f58c4d 100644
--- a/src/random.h
+++ b/src/random.h
@@ -6,6 +6,7 @@
 #ifndef BITCOIN_RANDOM_H
 #define BITCOIN_RANDOM_H
 
+#include "crypto/chacha20.h"
 #include "uint256.h"
 
 #include <stdint.h>
@@ -33,21 +34,68 @@ void GetStrongRandBytes(unsigned char* buf, int num);
  * This class is not thread-safe.
  */
 class FastRandomContext {
+private:
+    bool requires_seed;
+    ChaCha20 rng;
+
+    unsigned char bytebuf[64];
+    int bytebuf_size;
+
+    uint64_t bitbuf;
+    int bitbuf_size;
+
+    void RandomSeed();
+
+    void FillByteBuffer()
+    {
+        if (requires_seed) {
+            RandomSeed();
+        }
+        rng.Output(bytebuf, sizeof(bytebuf));
+        bytebuf_size = sizeof(bytebuf);
+    }
+
+    void FillBitBuffer()
+    {
+        bitbuf = rand64();
+        bitbuf_size = 64;
+    }
+
 public:
-    explicit FastRandomContext(bool fDeterministic=false);
+    explicit FastRandomContext(bool fDeterministic = false);
 
-    uint32_t rand32() {
-        Rz = 36969 * (Rz & 65535) + (Rz >> 16);
-        Rw = 18000 * (Rw & 65535) + (Rw >> 16);
-        return (Rw << 16) + Rz;
+    /** Initialize with explicit seed (only for testing) */
+    explicit FastRandomContext(const uint256& seed);
+
+    /** Generate a random 64-bit integer. */
+    uint64_t rand64()
+    {
+        if (bytebuf_size < 8) FillByteBuffer();
+        uint64_t ret = ReadLE64(bytebuf + 64 - bytebuf_size);
+        bytebuf_size -= 8;
+        return ret;
     }
 
-    bool randbool() {
-        return rand32() & 1;
+    /** Generate a random (bits)-bit integer. */
+    uint64_t randbits(int bits) {
+        if (bits == 0) {
+            return 0;
+        } else if (bits > 32) {
+            return rand64() >> (64 - bits);
+        } else {
+            if (bitbuf_size < bits) FillBitBuffer();
+            uint64_t ret = bitbuf & (~(uint64_t)0 >> (64 - bits));
+            bitbuf >>= bits;
+            bitbuf_size -= bits;
+            return ret;
+        }
     }
 
-    uint32_t Rz;
-    uint32_t Rw;
+    /** Generate a random 32-bit integer. */
+    uint32_t rand32() { return randbits(32); }
+
+    /** Generate a random boolean. */
+    bool randbool() { return randbits(1); }
 };
 
 /* Number of random bytes returned by GetOSRand.
diff --git a/src/test/addrman_tests.cpp b/src/test/addrman_tests.cpp
index 5d1c5b78d..39fa381dd 100644
--- a/src/test/addrman_tests.cpp
+++ b/src/test/addrman_tests.cpp
@@ -203,10 +203,11 @@ BOOST_AUTO_TEST_CASE(addrman_select)
     BOOST_CHECK(addrman.size() == 7);
 
     // Test 12: Select pulls from new and tried regardless of port number.
-    BOOST_CHECK(addrman.Select().ToString() == "250.4.6.6:8333");
-    BOOST_CHECK(addrman.Select().ToString() == "250.3.2.2:9999");
-    BOOST_CHECK(addrman.Select().ToString() == "250.3.3.3:9999");
-    BOOST_CHECK(addrman.Select().ToString() == "250.4.4.4:8333");
+    std::set<uint16_t> ports;
+    for (int i = 0; i < 20; ++i) {
+        ports.insert(addrman.Select().GetPort());
+    }
+    BOOST_CHECK_EQUAL(ports.size(), 3);
 }
 
 BOOST_AUTO_TEST_CASE(addrman_new_collisions)
diff --git a/src/test/prevector_tests.cpp b/src/test/prevector_tests.cpp
index bd8a7819a..cfed5e347 100644
--- a/src/test/prevector_tests.cpp
+++ b/src/test/prevector_tests.cpp
@@ -28,6 +28,7 @@ class prevector_tester {
     typedef typename pretype::size_type Size;
     bool passed = true;
     FastRandomContext rand_cache;
+    uint256 rand_seed;
 
 
     template <typename A, typename B>
@@ -183,13 +184,12 @@ public:
     }
 
     ~prevector_tester() {
-        BOOST_CHECK_MESSAGE(passed, "insecure_rand_Rz: "
-                << rand_cache.Rz
-                << ", insecure_rand_Rw: "
-                << rand_cache.Rw);
+        BOOST_CHECK_MESSAGE(passed, "insecure_rand: " + rand_seed.ToString());
     }
+
     prevector_tester() {
         seed_insecure_rand();
+        rand_seed = insecure_rand_seed;
         rand_cache = insecure_rand_ctx;
     }
 };
diff --git a/src/test/random_tests.cpp b/src/test/random_tests.cpp
index d2c46c0da..31b993cd3 100644
--- a/src/test/random_tests.cpp
+++ b/src/test/random_tests.cpp
@@ -15,5 +15,24 @@ BOOST_AUTO_TEST_CASE(osrandom_tests)
     BOOST_CHECK(Random_SanityCheck());
 }
 
-BOOST_AUTO_TEST_SUITE_END()
+BOOST_AUTO_TEST_CASE(fastrandom_tests)
+{
+    // Check that deterministic FastRandomContexts are deterministic
+    FastRandomContext ctx1(true);
+    FastRandomContext ctx2(true);
 
+    BOOST_CHECK_EQUAL(ctx1.rand32(), ctx2.rand32());
+    BOOST_CHECK_EQUAL(ctx1.rand32(), ctx2.rand32());
+    BOOST_CHECK_EQUAL(ctx1.rand64(), ctx2.rand64());
+    BOOST_CHECK_EQUAL(ctx1.randbits(3), ctx2.randbits(3));
+    BOOST_CHECK_EQUAL(ctx1.randbits(7), ctx2.randbits(7));
+    BOOST_CHECK_EQUAL(ctx1.rand32(), ctx2.rand32());
+    BOOST_CHECK_EQUAL(ctx1.randbits(3), ctx2.randbits(3));
+
+    // Check that a nondeterministic ones are not
+    FastRandomContext ctx3;
+    FastRandomContext ctx4;
+    BOOST_CHECK(ctx3.rand64() != ctx4.rand64()); // extremely unlikely to be equal
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index abaec45cd..48593f62d 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -27,7 +27,8 @@
 #include <boost/filesystem.hpp>
 #include <boost/thread.hpp>
 
-FastRandomContext insecure_rand_ctx(true);
+uint256 insecure_rand_seed = GetRandHash();
+FastRandomContext insecure_rand_ctx(insecure_rand_seed);
 
 extern bool fPrintToConsole;
 extern void noui_connect();
diff --git a/src/test/test_random.h b/src/test/test_random.h
index 4a1637ac7..318c44df4 100644
--- a/src/test/test_random.h
+++ b/src/test/test_random.h
@@ -8,11 +8,17 @@
 
 #include "random.h"
 
+extern uint256 insecure_rand_seed;
 extern FastRandomContext insecure_rand_ctx;
 
 static inline void seed_insecure_rand(bool fDeterministic = false)
 {
-    insecure_rand_ctx = FastRandomContext(fDeterministic);
+    if (fDeterministic) {
+        insecure_rand_seed = uint256();
+    } else {
+        insecure_rand_seed = GetRandHash();
+    }
+    insecure_rand_ctx = FastRandomContext(insecure_rand_seed);
 }
 
 static inline uint32_t insecure_rand(void)

From 4fd2d2fc97e21efceab849576e544160fd5e3e3d Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sat, 25 Feb 2017 12:16:58 -0800
Subject: [PATCH 5/5] Add a FastRandomContext::randrange and use it

---
 configure.ac              |  2 ++
 src/bench/checkqueue.cpp  |  2 +-
 src/crypto/common.h       | 21 +++++++++++++++++++++
 src/net.h                 |  2 +-
 src/random.h              | 12 ++++++++++++
 src/test/crypto_tests.cpp | 23 +++++++++++++++++++++++
 src/test/random_tests.cpp | 15 +++++++++++++++
 7 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 2a9ee018a..42b8448cf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -550,6 +550,8 @@ AC_CHECK_DECLS([bswap_16, bswap_32, bswap_64],,,
                  #include <byteswap.h>
                  #endif])
 
+AC_CHECK_DECLS([__builtin_clz, __builtin_clzl, __builtin_clzll])
+
 dnl Check for MSG_NOSIGNAL
 AC_MSG_CHECKING(for MSG_NOSIGNAL)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/socket.h>]],
diff --git a/src/bench/checkqueue.cpp b/src/bench/checkqueue.cpp
index 6fa9fe4fe..88a2a570f 100644
--- a/src/bench/checkqueue.cpp
+++ b/src/bench/checkqueue.cpp
@@ -68,7 +68,7 @@ static void CCheckQueueSpeedPrevectorJob(benchmark::State& state)
         PrevectorJob(){
         }
         PrevectorJob(FastRandomContext& insecure_rand){
-            p.resize(insecure_rand.rand32() % (PREVECTOR_SIZE*2));
+            p.resize(insecure_rand.randrange(PREVECTOR_SIZE*2));
         }
         bool operator()()
         {
diff --git a/src/crypto/common.h b/src/crypto/common.h
index 4a9d1150b..bcca3d30e 100644
--- a/src/crypto/common.h
+++ b/src/crypto/common.h
@@ -79,4 +79,25 @@ void static inline WriteBE64(unsigned char* ptr, uint64_t x)
     memcpy(ptr, (char*)&v, 8);
 }
 
+/** Return the smallest number n such that (x >> n) == 0 (or 64 if the highest bit in x is set. */
+uint64_t static inline CountBits(uint64_t x)
+{
+#ifdef HAVE_DECL___BUILTIN_CLZL
+    if (sizeof(unsigned long) >= sizeof(uint64_t)) {
+        return x ? 8 * sizeof(unsigned long) - __builtin_clzl(x) : 0;
+    }
+#endif
+#ifdef HAVE_DECL___BUILTIN_CLZLL
+    if (sizeof(unsigned long long) >= sizeof(uint64_t)) {
+        return x ? 8 * sizeof(unsigned long long) - __builtin_clzll(x) : 0;
+    }
+#endif
+    int ret = 0;
+    while (x) {
+        x >>= 1;
+        ++ret;
+    }
+    return ret;
+}
+
 #endif // BITCOIN_CRYPTO_COMMON_H
diff --git a/src/net.h b/src/net.h
index 3bbe38617..c5360f9b5 100644
--- a/src/net.h
+++ b/src/net.h
@@ -760,7 +760,7 @@ public:
         // after addresses were pushed.
         if (_addr.IsValid() && !addrKnown.contains(_addr.GetKey())) {
             if (vAddrToSend.size() >= MAX_ADDR_TO_SEND) {
-                vAddrToSend[insecure_rand.rand32() % vAddrToSend.size()] = _addr;
+                vAddrToSend[insecure_rand.randrange(vAddrToSend.size())] = _addr;
             } else {
                 vAddrToSend.push_back(_addr);
             }
diff --git a/src/random.h b/src/random.h
index 077f58c4d..9551e1c46 100644
--- a/src/random.h
+++ b/src/random.h
@@ -7,6 +7,7 @@
 #define BITCOIN_RANDOM_H
 
 #include "crypto/chacha20.h"
+#include "crypto/common.h"
 #include "uint256.h"
 
 #include <stdint.h>
@@ -91,6 +92,17 @@ public:
         }
     }
 
+    /** Generate a random integer in the range [0..range). */
+    uint64_t randrange(uint64_t range)
+    {
+        --range;
+        int bits = CountBits(range);
+        while (true) {
+            uint64_t ret = randbits(bits);
+            if (ret <= range) return ret;
+        }
+    }
+
     /** Generate a random 32-bit integer. */
     uint32_t rand32() { return randbits(32); }
 
diff --git a/src/test/crypto_tests.cpp b/src/test/crypto_tests.cpp
index a20182afb..72e562808 100644
--- a/src/test/crypto_tests.cpp
+++ b/src/test/crypto_tests.cpp
@@ -10,6 +10,7 @@
 #include "crypto/sha512.h"
 #include "crypto/hmac_sha256.h"
 #include "crypto/hmac_sha512.h"
+#include "random.h"
 #include "utilstrencodings.h"
 #include "test/test_bitcoin.h"
 #include "test/test_random.h"
@@ -484,4 +485,26 @@ BOOST_AUTO_TEST_CASE(chacha20_testvector)
                  "fab78c9");
 }
 
+BOOST_AUTO_TEST_CASE(countbits_tests)
+{
+    FastRandomContext ctx;
+    for (int i = 0; i <= 64; ++i) {
+        if (i == 0) {
+            // Check handling of zero.
+            BOOST_CHECK_EQUAL(CountBits(0), 0);
+        } else if (i < 10) {
+            for (uint64_t j = 1 << (i - 1); (j >> i) == 0; ++j) {
+                // Exhaustively test up to 10 bits
+                BOOST_CHECK_EQUAL(CountBits(j), i);
+            }
+        } else {
+            for (int k = 0; k < 1000; k++) {
+                // Randomly test 1000 samples of each length above 10 bits.
+                uint64_t j = ((uint64_t)1) << (i - 1) | ctx.randbits(i - 1);
+                BOOST_CHECK_EQUAL(CountBits(j), i);
+            }
+        }
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/random_tests.cpp b/src/test/random_tests.cpp
index 31b993cd3..859673422 100644
--- a/src/test/random_tests.cpp
+++ b/src/test/random_tests.cpp
@@ -35,4 +35,19 @@ BOOST_AUTO_TEST_CASE(fastrandom_tests)
     BOOST_CHECK(ctx3.rand64() != ctx4.rand64()); // extremely unlikely to be equal
 }
 
+BOOST_AUTO_TEST_CASE(fastrandom_randbits)
+{
+    FastRandomContext ctx1;
+    FastRandomContext ctx2;
+    for (int bits = 0; bits < 63; ++bits) {
+        for (int j = 0; j < 1000; ++j) {
+            uint64_t rangebits = ctx1.randbits(bits);
+            BOOST_CHECK_EQUAL(rangebits >> bits, 0);
+            uint64_t range = ((uint64_t)1) << bits | rangebits;
+            uint64_t rand = ctx2.randrange(range);
+            BOOST_CHECK(rand < range);
+        }
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()