fuzz coverage

// Copyright (c) 2019-present 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_POLY1305_H

#define BITCOIN_CRYPTO_POLY1305_H

#include <span.h>

#include <cassert>

#include <cstdlib>

#include <stdint.h>

#define POLY1305_BLOCK_SIZE 16

namespace poly1305_donna {

// Based on the public domain implementation by Andrew Moon

// poly1305-donna-32.h from https://github.com/floodyberry/poly1305-donna

typedef struct {

    uint32_t r[5];

    uint32_t h[5];

    uint32_t pad[4];

    size_t leftover;

    unsigned char buffer[POLY1305_BLOCK_SIZE];

    unsigned char final;

} poly1305_context;

void poly1305_init(poly1305_context *st, const unsigned char key[32]) noexcept;

void poly1305_update(poly1305_context *st, const unsigned char *m, size_t bytes) noexcept;

void poly1305_finish(poly1305_context *st, unsigned char mac[16]) noexcept;

}  // namespace poly1305_donna

/** C++ wrapper with std::byte span interface around poly1305_donna code. */

class Poly1305

{

    poly1305_donna::poly1305_context m_ctx;

public:

    /** Length of the output produced by Finalize(). */

    static constexpr unsigned TAGLEN{16};

    /** Length of the keys expected by the constructor. */

    static constexpr unsigned KEYLEN{32};

    /** Construct a Poly1305 object with a given 32-byte key. */

    Poly1305(std::span<const std::byte> key) noexcept

    {

        assert(key.size() == KEYLEN);

        poly1305_donna::poly1305_init(&m_ctx, UCharCast(key.data()));

    }

    /** Process message bytes. */

    Poly1305& Update(std::span<const std::byte> msg) noexcept

    {

        poly1305_donna::poly1305_update(&m_ctx, UCharCast(msg.data()), msg.size());

        return *this;

    }

    /** Write authentication tag to 16-byte out. */

    void Finalize(std::span<std::byte> out) noexcept

    {

        assert(out.size() == TAGLEN);

        poly1305_donna::poly1305_finish(&m_ctx, UCharCast(out.data()));

    }

};

#endif // BITCOIN_CRYPTO_POLY1305_H