sha256.h

#pragma once
#include <cstdint>
#include <array>
#include <string>



/// <summary>
/// The hash functions specified herein are used to compute a message
/// digest for a message or data file that is provided as input.The
/// message or data file should be considered to be a bit string.The
/// length of the message is the number of bits in the message(the empty 
/// message has length 0).
/// 
/// The details can be found here:
/// https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
/// </summary>
class SHA256
{
  public:
    SHA256();
    void update(const std::string& message);
    void update(const std::uint8_t* data, std::size_t length);
    std::uint8_t* digest();
    static std::string toString(const uint8_t* digest);


  private:


    /// <summary>
    /// The SHA works with 512 bit chunks of data. m_DataChunk is therefore a byte array with a len of 64 (and thus 512 bits)
    /// </summary>
    std::uint8_t m_DataChunk[64];


    /// <summary>
    /// The length of the current "processing" block 
    /// </summary>
    std::uint32_t m_BlockLength;


    /// <summary>
    /// While block length will reset each 64 bytes, this message length keeps total track of the processed message 
    /// </summary>
    std::uint64_t m_MessageLength;


    /// <summary>
    /// m_H will hold the hash values as the digest is processed
    /// </summary>
    uint32_t m_H[8];


    /// <summary>
    /// SHA-224 and SHA-256 use the same sequence of sixty-four constant 32-bit words, 
    /// These words represent the first thirty - two bits of the fractional parts of
    /// the cube roots of the first sixty - four prime numbers.In hex, these constant words are (from left
    /// to right)
    /// </summary>
    static constexpr std::array<uint32_t, 64> K = {
      0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,
      0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
      0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,
      0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
      0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,
      0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
      0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,
      0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
      0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,
      0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
      0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,
      0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
      0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,
      0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
      0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,
      0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
    };

  private:

    /*
    SHA-256 uses six logical functions, where each function
    operates on 32-bit words, which are represented as x, y, and z.  The
    result of each function is a new 32-bit word.
    */


    /// <summary>
    /// Pad works on the final block of data. It is called when the digest is requested
    /// </summary>
    void pad();


    /// <summary>
    /// Works on the 512bit block of data, separating it out in 16 32-bit words. It then
    /// create an additional 48 32-bit words using the sha functions. Transform is only called
    /// on appropriately padded blocks
    /// </summary>
    void transform();



    void order(uint8_t* hash);


    /// <summary>
    /// CHOOSE(x, y, z) = (x AND y) XOR ( (NOT x) AND z)
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="z"></param>
    /// <returns></returns>
    std::uint32_t choose(std::uint32_t x, std::uint32_t y, std::uint32_t z);


    /// <summary>
    /// MAJORITY(x, y, z) = (x AND y) XOR (x AND z) XOR (y AND z)
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="z"></param>
    /// <returns></returns>
    std::uint32_t majority(std::uint32_t x, std::uint32_t y, std::uint32_t z);


    /// <summary>
    /// BSIG0(x) = ROTR^2(x) XOR ROTR^13(x) XOR ROTR^22(x)
    /// </summary>
    /// <param name="x"></param>
    /// <returns></returns>
    std::uint32_t bsigma0(std::uint32_t x);


    /// <summary>
    /// BSIG1(x) = ROTR^6(x) XOR ROTR^11(x) XOR ROTR^25(x)
    /// </summary>
    /// <param name="x"></param>
    /// <returns></returns>
    std::uint32_t bsigma1(std::uint32_t x);


    /// <summary>
    /// SSIG0(x) = ROTR^7(x) XOR ROTR^18(x) XOR SHR^3(x)
    /// 1. Rotate right the word by 7
    /// 2. Rotate right the word by 18 and XOR with step 1
    /// 3. Shift the word right by 3 and XOR with step 2
    /// </summary>
    /// <param name="x">32 bit word</param>
    /// <returns></returns>
    std::uint32_t ssigma0(std::uint32_t x);


    /// <summary>
    /// SSIG1(x) = ROTR^17(x) XOR ROTR^19(x) XOR SHR^10(x)
    /// </summary>
    /// <param name="x"></param>
    /// <returns></returns>
    std::uint32_t ssigma1(std::uint32_t x);


    /// <summary>
    /// The rotate right function performs a bitshift right operation - (x>>n) OR (x<<(w-n))
    /// </summary>
    /// <param name="x">A 32 bit word</param>
    /// <param name="n"></param>
    /// <returns></returns>
    std::uint32_t ROTR(std::uint32_t x, std::uint32_t n);

    /// <summary>
    /// The rotate right function performs a bitshift right operation - (x>>n) OR (x<<(w-n))
    /// </summary>
    /// <param name="x"></param>
    /// <param name="n"></param>
    /// <returns></returns>
    std::uint32_t ROTL(std::uint32_t x, std::uint32_t n);


};