Merge #9792: FastRandomContext improvements and switch to ChaCha20

4fd2d2f Add a FastRandomContext::randrange and use it (Pieter Wuille)
1632922 Switch FastRandomContext to ChaCha20 (Pieter Wuille)
e04326f Add ChaCha20 (Pieter Wuille)
663fbae FastRandom benchmark (Pieter Wuille)
c21cbe6 Introduce FastRandomContext::randbool() (Pieter Wuille)

Tree-SHA512: 7fff61e3f6d6dc6ac846ca643d877b377db609646dd401a0e8f50b052c6b9bcd2f5fc34de6bbf28f04afd1724f6279ee163ead5f37d724fb782a00239f35db1d

3 files changed, 227 insertions, 0 deletions

diff --git a/src/crypto/chacha20.cpp b/src/crypto/chacha20.cpp
new file mode 100644
index 0000000000..816ae870e1
--- /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 0000000000..a305977bcd
--- /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/crypto/common.h b/src/crypto/common.h
index 4a9d1150b6..bcca3d30ea 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