core.cxxm

/// SPDX-License-Identifier: Apache 2.0
/// @file crypto/sha256.cxxm
/// @brief SHA-256 streaming hash implementation
 
export module crypto.sha256.core;
import zxfoundation.base.types;
import lib.error;
import std;
 
export {
 
namespace crypto::sha256 {
 
    /// @brief Byte length of a SHA-256 message digest.
    constexpr auto SHA256_DIGEST_SIZE = 32U;
 
    /// @brief SHA-256 running computation context.
    struct sha256_ctx {
        u32  state[8]{};      ///< Current intermediate hash values (H0..H7).
        u64  bit_count{};     ///< Total message bits processed so far.
        u8   buf[64]{};       ///< Partial-block accumulation buffer.
        u32  buf_len{};       ///< Number of valid bytes in buf (0..63).
        bool finalized{};     ///< Set by sha256_final(); guards against double-finalize.
    };
 
    /// @brief Initialize a SHA-256 context to the FIPS 180-4 initial hash value.
    /// @param[out] ctx  Context to initialize.
    auto sha256_init(sha256_ctx& ctx) -> void;
 
    /// @brief Feed a span of bytes into a running SHA-256 computation.
    /// @param[in,out] ctx   Running SHA-256 context.
    /// @param[in]     data  Input byte span.
    /// @return std::expected<void, lib::kernel_error>
    auto sha256_update(sha256_ctx& ctx, std::span<const u8> data)
        -> std::expected<void, lib::kernel_error>;
 
    /// @brief Finalize the hash and write the 32-byte digest.
    /// @param[in,out] ctx  Running SHA-256 context.
    /// @param[out]    out  Exactly 32-byte output span.
    /// @return std::expected<void, lib::kernel_error>
    auto sha256_final(sha256_ctx& ctx, std::span<u8, SHA256_DIGEST_SIZE> out)
        -> std::expected<void, lib::kernel_error>;
 
    /// @brief One-shot SHA-256: hash @p data and write the 32-byte digest to @p out.
    [[nodiscard]] auto sha256_hash(std::span<const u8> data, std::span<u8, SHA256_DIGEST_SIZE> out)
        -> std::expected<void, lib::kernel_error>;
 
    [[nodiscard]] auto sha256_verify(std::span<const u8> data,
                                     std::span<const u8, SHA256_DIGEST_SIZE> expected)
        -> std::expected<void, lib::kernel_error>;
 
} // namespace crypto::sha256
 
} // end export