Inside Bitcoin

1// Copyright (c) 2022-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#include <bench/bench.h>
6#include <key.h>
7#include <pubkey.h>
8#include <random.h>
9#include <span.h>
10
11#include <algorithm>
12#include <array>
13#include <cstddef>
14#include <span>
15
16static void BIP324_ECDH(benchmark::Bench& bench)
17{
18    ECC_Context ecc_context{};
19    FastRandomContext rng;
20
21    std::array<std::byte, 32> key_data;
22    std::array<std::byte, EllSwiftPubKey::size()> our_ellswift_data;
23    std::array<std::byte, EllSwiftPubKey::size()> their_ellswift_data;
24
25    rng.fillrand(key_data);
26    rng.fillrand(our_ellswift_data);
27    rng.fillrand(their_ellswift_data);
28
29    bench.batch(1).unit("ecdh").run([&] {
30        CKey key;
31        key.Set(key_data.data(), key_data.data() + 32, true);
32        EllSwiftPubKey our_ellswift(our_ellswift_data);
33        EllSwiftPubKey their_ellswift(their_ellswift_data);
34
35        auto ret = key.ComputeBIP324ECDHSecret(their_ellswift, our_ellswift, true);
36
37        // To make sure that the computation is not the same on every iteration (ellswift decoding
38        // is variable-time), distribute bytes from the shared secret over the 3 inputs. The most
39        // important one is their_ellswift, because that one is actually decoded, so it's given most
40        // bytes. The data is copied into the middle, so that both halves are affected:
41        // - Copy 8 bytes from the resulting shared secret into middle of the private key.
42        std::copy(ret.begin(), ret.begin() + 8, key_data.begin() + 12);
43        // - Copy 8 bytes from the resulting shared secret into the middle of our ellswift key.
44        std::copy(ret.begin() + 8, ret.begin() + 16, our_ellswift_data.begin() + 28);
45        // - Copy 16 bytes from the resulting shared secret into the middle of their ellswift key.
46        std::copy(ret.begin() + 16, ret.end(), their_ellswift_data.begin() + 24);
47    });
48}
49
50BENCHMARK(BIP324_ECDH);
51