Merge bitcoin/bitcoin#22704: fuzz: Differential fuzzing to compare Bitcoin Core's and D. J. Bernstein's implementation of ChaCha20

4d0ac72f3ae78e3c6a0d5dc4f7e809583abd0546 [fuzz] Add fuzzing harness to compare both implementations of ChaCha20 (stratospher)
65ef93203cc6a977c8e96f07cb9155f46faf5004 [fuzz] Add D. J. Bernstein's implementation of ChaCha20 (stratospher)

Pull request description:

  This PR compares Bitcoin Core's implementation of ChaCha20 with D. J. Bernstein's in order to find implementation discrepancies if any.

ACKs for top commit:
  laanwj:
    Code review ACK 4d0ac72f3ae78e3c6a0d5dc4f7e809583abd0546

Tree-SHA512: f826144b4db61b9cbdd7efaaca8fa9cbb899953065bc8a26820a566303b2ab6a17431e7c114635789f0a63fbe3b65cb0bf2ab85baf882803a5ee172af4881544

2 files changed, 331 insertions, 0 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 326409c078..9fe2a3cf8a 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -239,6 +239,7 @@ test_fuzz_fuzz_SOURCES = \
  test/fuzz/crypto_chacha20.cpp \
  test/fuzz/crypto_chacha20_poly1305_aead.cpp \
  test/fuzz/crypto_common.cpp \
+ test/fuzz/crypto_diff_fuzz_chacha20.cpp \
  test/fuzz/crypto_hkdf_hmac_sha256_l32.cpp \
  test/fuzz/crypto_poly1305.cpp \
  test/fuzz/cuckoocache.cpp \
diff --git a/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp b/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp
new file mode 100644
index 0000000000..96681a121a
--- /dev/null
+++ b/src/test/fuzz/crypto_diff_fuzz_chacha20.cpp
@@ -0,0 +1,330 @@
+// Copyright (c) 2020-2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <crypto/chacha20.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <vector>
+
+/*
+From https://cr.yp.to/chacha.html
+chacha-merged.c version 20080118
+D. J. Bernstein
+Public domain.
+*/
+
+typedef unsigned int u32;
+typedef unsigned char u8;
+
+#define U8C(v) (v##U)
+#define U32C(v) (v##U)
+
+#define U8V(v) ((u8)(v)&U8C(0xFF))
+#define U32V(v) ((u32)(v)&U32C(0xFFFFFFFF))
+
+#define ROTL32(v, n) (U32V((v) << (n)) | ((v) >> (32 - (n))))
+
+#define U8TO32_LITTLE(p)                                              \
+    (((u32)((p)[0])) | ((u32)((p)[1]) << 8) | ((u32)((p)[2]) << 16) | \
+     ((u32)((p)[3]) << 24))
+
+#define U32TO8_LITTLE(p, v)      \
+    do {                         \
+        (p)[0] = U8V((v));       \
+        (p)[1] = U8V((v) >> 8);  \
+        (p)[2] = U8V((v) >> 16); \
+        (p)[3] = U8V((v) >> 24); \
+    } while (0)
+
+/* ------------------------------------------------------------------------- */
+/* Data structures */
+
+typedef struct
+{
+    u32 input[16];
+} ECRYPT_ctx;
+
+/* ------------------------------------------------------------------------- */
+/* Mandatory functions */
+
+void ECRYPT_keysetup(
+    ECRYPT_ctx* ctx,
+    const u8* key,
+    u32 keysize, /* Key size in bits. */
+    u32 ivsize); /* IV size in bits. */
+
+void ECRYPT_ivsetup(
+    ECRYPT_ctx* ctx,
+    const u8* iv);
+
+void ECRYPT_encrypt_bytes(
+    ECRYPT_ctx* ctx,
+    const u8* plaintext,
+    u8* ciphertext,
+    u32 msglen); /* Message length in bytes. */
+
+/* ------------------------------------------------------------------------- */
+
+/* Optional features */
+
+void ECRYPT_keystream_bytes(
+    ECRYPT_ctx* ctx,
+    u8* keystream,
+    u32 length); /* Length of keystream in bytes. */
+
+/* ------------------------------------------------------------------------- */
+
+#define ROTATE(v, c) (ROTL32(v, c))
+#define XOR(v, w) ((v) ^ (w))
+#define PLUS(v, w) (U32V((v) + (w)))
+#define PLUSONE(v) (PLUS((v), 1))
+
+#define QUARTERROUND(a, b, c, d) \
+    a = PLUS(a, b); d = ROTATE(XOR(d, a), 16);   \
+    c = PLUS(c, d); b = ROTATE(XOR(b, c), 12);   \
+    a = PLUS(a, b); d = ROTATE(XOR(d, a), 8);    \
+    c = PLUS(c, d); b = ROTATE(XOR(b, c), 7);
+
+static const char sigma[] = "expand 32-byte k";
+static const char tau[] = "expand 16-byte k";
+
+void ECRYPT_keysetup(ECRYPT_ctx* x, const u8* k, u32 kbits, u32 ivbits)
+{
+    const char* constants;
+
+    x->input[4] = U8TO32_LITTLE(k + 0);
+    x->input[5] = U8TO32_LITTLE(k + 4);
+    x->input[6] = U8TO32_LITTLE(k + 8);
+    x->input[7] = U8TO32_LITTLE(k + 12);
+    if (kbits == 256) { /* recommended */
+        k += 16;
+        constants = sigma;
+    } else { /* kbits == 128 */
+        constants = tau;
+    }
+    x->input[8] = U8TO32_LITTLE(k + 0);
+    x->input[9] = U8TO32_LITTLE(k + 4);
+    x->input[10] = U8TO32_LITTLE(k + 8);
+    x->input[11] = U8TO32_LITTLE(k + 12);
+    x->input[0] = U8TO32_LITTLE(constants + 0);
+    x->input[1] = U8TO32_LITTLE(constants + 4);
+    x->input[2] = U8TO32_LITTLE(constants + 8);
+    x->input[3] = U8TO32_LITTLE(constants + 12);
+}
+
+void ECRYPT_ivsetup(ECRYPT_ctx* x, const u8* iv)
+{
+    x->input[12] = 0;
+    x->input[13] = 0;
+    x->input[14] = U8TO32_LITTLE(iv + 0);
+    x->input[15] = U8TO32_LITTLE(iv + 4);
+}
+
+void ECRYPT_encrypt_bytes(ECRYPT_ctx* x, const u8* m, u8* c, u32 bytes)
+{
+    u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
+    u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
+    u8* ctarget = NULL;
+    u8 tmp[64];
+    uint32_t i;
+
+    if (!bytes) return;
+
+    j0 = x->input[0];
+    j1 = x->input[1];
+    j2 = x->input[2];
+    j3 = x->input[3];
+    j4 = x->input[4];
+    j5 = x->input[5];
+    j6 = x->input[6];
+    j7 = x->input[7];
+    j8 = x->input[8];
+    j9 = x->input[9];
+    j10 = x->input[10];
+    j11 = x->input[11];
+    j12 = x->input[12];
+    j13 = x->input[13];
+    j14 = x->input[14];
+    j15 = x->input[15];
+
+    for (;;) {
+        if (bytes < 64) {
+            for (i = 0; i < bytes; ++i)
+                tmp[i] = m[i];
+            m = tmp;
+            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 = PLUS(x0, j0);
+        x1 = PLUS(x1, j1);
+        x2 = PLUS(x2, j2);
+        x3 = PLUS(x3, j3);
+        x4 = PLUS(x4, j4);
+        x5 = PLUS(x5, j5);
+        x6 = PLUS(x6, j6);
+        x7 = PLUS(x7, j7);
+        x8 = PLUS(x8, j8);
+        x9 = PLUS(x9, j9);
+        x10 = PLUS(x10, j10);
+        x11 = PLUS(x11, j11);
+        x12 = PLUS(x12, j12);
+        x13 = PLUS(x13, j13);
+        x14 = PLUS(x14, j14);
+        x15 = PLUS(x15, j15);
+
+        x0 = XOR(x0, U8TO32_LITTLE(m + 0));
+        x1 = XOR(x1, U8TO32_LITTLE(m + 4));
+        x2 = XOR(x2, U8TO32_LITTLE(m + 8));
+        x3 = XOR(x3, U8TO32_LITTLE(m + 12));
+        x4 = XOR(x4, U8TO32_LITTLE(m + 16));
+        x5 = XOR(x5, U8TO32_LITTLE(m + 20));
+        x6 = XOR(x6, U8TO32_LITTLE(m + 24));
+        x7 = XOR(x7, U8TO32_LITTLE(m + 28));
+        x8 = XOR(x8, U8TO32_LITTLE(m + 32));
+        x9 = XOR(x9, U8TO32_LITTLE(m + 36));
+        x10 = XOR(x10, U8TO32_LITTLE(m + 40));
+        x11 = XOR(x11, U8TO32_LITTLE(m + 44));
+        x12 = XOR(x12, U8TO32_LITTLE(m + 48));
+        x13 = XOR(x13, U8TO32_LITTLE(m + 52));
+        x14 = XOR(x14, U8TO32_LITTLE(m + 56));
+        x15 = XOR(x15, U8TO32_LITTLE(m + 60));
+
+        j12 = PLUSONE(j12);
+        if (!j12) {
+            j13 = PLUSONE(j13);
+            /* stopping at 2^70 bytes per nonce is user's responsibility */
+        }
+
+        U32TO8_LITTLE(c + 0, x0);
+        U32TO8_LITTLE(c + 4, x1);
+        U32TO8_LITTLE(c + 8, x2);
+        U32TO8_LITTLE(c + 12, x3);
+        U32TO8_LITTLE(c + 16, x4);
+        U32TO8_LITTLE(c + 20, x5);
+        U32TO8_LITTLE(c + 24, x6);
+        U32TO8_LITTLE(c + 28, x7);
+        U32TO8_LITTLE(c + 32, x8);
+        U32TO8_LITTLE(c + 36, x9);
+        U32TO8_LITTLE(c + 40, x10);
+        U32TO8_LITTLE(c + 44, x11);
+        U32TO8_LITTLE(c + 48, x12);
+        U32TO8_LITTLE(c + 52, x13);
+        U32TO8_LITTLE(c + 56, x14);
+        U32TO8_LITTLE(c + 60, x15);
+
+        if (bytes <= 64) {
+            if (bytes < 64) {
+                for (i = 0; i < bytes; ++i)
+                    ctarget[i] = c[i];
+            }
+            x->input[12] = j12;
+            x->input[13] = j13;
+            return;
+        }
+        bytes -= 64;
+        c += 64;
+        m += 64;
+    }
+}
+
+void ECRYPT_keystream_bytes(ECRYPT_ctx* x, u8* stream, u32 bytes)
+{
+    u32 i;
+    for (i = 0; i < bytes; ++i)
+        stream[i] = 0;
+    ECRYPT_encrypt_bytes(x, stream, stream, bytes);
+}
+
+FUZZ_TARGET(crypto_diff_fuzz_chacha20)
+{
+    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
+
+    ChaCha20 chacha20;
+    ECRYPT_ctx ctx;
+    // D. J. Bernstein doesn't initialise ctx to 0 while Bitcoin Core initialises chacha20 to 0 in the constructor
+    for (int i = 0; i < 16; i++) {
+        ctx.input[i] = 0;
+    }
+
+    if (fuzzed_data_provider.ConsumeBool()) {
+        const std::vector<unsigned char> key = ConsumeFixedLengthByteVector(fuzzed_data_provider, fuzzed_data_provider.ConsumeIntegralInRange<size_t>(16, 32));
+        chacha20 = ChaCha20{key.data(), key.size()};
+        ECRYPT_keysetup(&ctx, key.data(), key.size() * 8, 0);
+        // ECRYPT_keysetup() doesn't set the counter and nonce to 0 while SetKey() does
+        uint8_t iv[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+        ECRYPT_ivsetup(&ctx, iv);
+    }
+
+    LIMITED_WHILE (fuzzed_data_provider.ConsumeBool(), 3000) {
+        CallOneOf(
+            fuzzed_data_provider,
+            [&] {
+                const std::vector<unsigned char> key = ConsumeFixedLengthByteVector(fuzzed_data_provider, fuzzed_data_provider.ConsumeIntegralInRange<size_t>(16, 32));
+                chacha20.SetKey(key.data(), key.size());
+                ECRYPT_keysetup(&ctx, key.data(), key.size() * 8, 0);
+                // ECRYPT_keysetup() doesn't set the counter and nonce to 0 while SetKey() does
+                uint8_t iv[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+                ECRYPT_ivsetup(&ctx, iv);
+            },
+            [&] {
+                uint64_t iv = fuzzed_data_provider.ConsumeIntegral<uint64_t>();
+                chacha20.SetIV(iv);
+                ctx.input[14] = iv;
+                ctx.input[15] = iv >> 32;
+            },
+            [&] {
+                uint64_t counter = fuzzed_data_provider.ConsumeIntegral<uint64_t>();
+                chacha20.Seek(counter);
+                ctx.input[12] = counter;
+                ctx.input[13] = counter >> 32;
+            },
+            [&] {
+                uint32_t integralInRange = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, 4096);
+                std::vector<uint8_t> output(integralInRange);
+                chacha20.Keystream(output.data(), output.size());
+                std::vector<uint8_t> djb_output(integralInRange);
+                ECRYPT_keystream_bytes(&ctx, djb_output.data(), djb_output.size());
+                if (output.data() != NULL && djb_output.data() != NULL) {
+                    assert(memcmp(output.data(), djb_output.data(), integralInRange) == 0);
+                }
+            },
+            [&] {
+                uint32_t integralInRange = fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, 4096);
+                std::vector<uint8_t> output(integralInRange);
+                const std::vector<uint8_t> input = ConsumeFixedLengthByteVector(fuzzed_data_provider, output.size());
+                chacha20.Crypt(input.data(), output.data(), input.size());
+                std::vector<uint8_t> djb_output(integralInRange);
+                ECRYPT_encrypt_bytes(&ctx, input.data(), djb_output.data(), input.size());
+            });
+    }
+}