SHA256 - без использования встроенных методов - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace SHA256
{
    public struct Digest
    {
        public uint H0, H1, H2, H3, H4, H5, H6, H7;
    }
 
    public class Sha256Digest
    {
        private byte[] buf, m;
        private Digest digest;
        private ulong messageLength, blocksQty;
        private uint[] W = new uint[64];
 
        public Sha256Digest()
        {
            initHs();
        }
 
        private void initHs()
        {
            /* SHA-256 initial hash value
            * The first 32 bits of the fractional parts of the square roots
            * of the first eight prime numbers
            */            
            digest.H0 = 0x6a09e667;
            digest.H1 = 0xbb67ae85;
            digest.H2 = 0x3c6ef372;
            digest.H3 = 0xa54ff53a;
            digest.H4 = 0x510e527f;
            digest.H5 = 0x9b05688c;
            digest.H6 = 0x1f83d9ab;
            digest.H7 = 0x5be0cd19;
        }
 
        /* SHA-256 Constants
        * (represent the first 32 bits of the fractional parts of the
        * cube roots of the first sixty-four prime numbers)
        */
        private static readonly uint[] 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
        };
 
        public Digest hash(byte[] message) { //operates only with byte-multiple messages 
            buf = new byte[message.LongLength];
            Array.Copy(message, buf, message.LongLength);
            messageLength = (ulong)message.LongLength;
            completeMessageLength();
            blocksQty = (ulong)m.LongLength / 64;
            for (ulong i = 0; i < blocksQty; i++)
            {
                expandBlock(i);
                processBlock();
            }             
            return digest;
        }
 
        private void completeMessageLength()
        {
            int zeroBitsToAddQty = 512 - (int)(((ulong)buf.LongLength * 8 + 1 + 64) % 512);
            m = new byte[((ulong)buf.LongLength * 8 + 1 + 64 + (ulong)zeroBitsToAddQty) / 8];
            Array.Copy(buf, m, buf.LongLength);
 
            m[buf.LongLength] = 128; //set 1-st bit to "1", 7 remaining to "0" (may not work with bit-multiple message!!)
 
            for (ulong i = (messageLength + 1); i < (ulong)m.LongLength; i++)
            {
                m[i] = 0;
            }
 
            byte[] messageBitLength_little_endian = BitConverter.GetBytes(messageLength * 8);
            byte[] messageBitLength_big_endian = new byte[messageBitLength_little_endian.Length];
            for (int i = 0, j = messageBitLength_little_endian.Length - 1; i < messageBitLength_little_endian.Length; i++, j--)
            {
                messageBitLength_big_endian[i] = messageBitLength_little_endian[j];
            }
            Array.Copy(messageBitLength_big_endian, 0, m, m.LongLength - 8, 8);
        }
 
        private void expandBlock(ulong blockNumber)
        {
            for (int i = 0; i < 16; i++)
            {
                W[i] = Bytes_To_UInt32(m, blockNumber * 64 + (ulong)i * 4);
            }
 
            for (int i = 16; i <= 63; i++)
            {
                W[i] = W[i - 16] + S0(W[i - 15]) + W[i - 7] + S1(W[i - 2]);
            }
        }
 
        internal static uint Bytes_To_UInt32(byte[] bs, ulong off)
        {
            uint n = (uint)bs[off] << 24;
            n |= (uint)bs[++off] << 16;
            n |= (uint)bs[++off] << 8;
            n |= (uint)bs[++off];
            return n;
        }
 
        private static uint rotr(uint x, int n)
        {
            return ((x >> n) | (x << 32 - n));
        }
 
        private static uint S0(uint x)
        {
            return rotr(x, 7) ^ rotr(x, 18) ^ (x >> 3);
        }
 
        private static uint S1(uint x)
        {
            return rotr(x, 17) ^ rotr(x, 19) ^ (x >> 10);
        }
 
        private static uint Ch(uint x, uint y, uint z) {
            return (x & y) ^ ((~x) & z);
        }
 
        private static uint Maj(uint x, uint y, uint z)
        {
            return (x & y) ^ (x & z) ^ (y & z);
        }
 
        private static uint E0(uint x)
        {
            return rotr(x, 2) ^ rotr(x, 13) ^ rotr(x, 22);
        }
 
        private static uint E1(uint x)
        {
            return rotr(x, 6) ^ rotr(x, 11) ^ rotr(x, 25);
        }
 
        private void processBlock()
        {             
            uint a = digest.H0;
            uint b = digest.H1;
            uint c = digest.H2;
            uint d = digest.H3;
            uint e = digest.H4;
            uint f = digest.H5;
            uint g = digest.H6;
            uint h = digest.H7;
 
            uint T1 = 0, T2 = 0;
 
            for (int i = 0; i < 64; i++)
            {
                T1 = h + E1(e) + Ch(e, f, g) + K[i] + W[i];
                T2 = E0(a) + Maj(a, b, c);
                h = g;
                g = f;
                f = e;
                e = d + T1;
                d = c;
                c = b;
                b = a;
                a = T1 + T2; 
            }
            digest.H0 += a;
            digest.H1 += b;
            digest.H2 += c;
            digest.H3 += d;
            digest.H4 += e;
            digest.H5 += f;
            digest.H6 += g;
            digest.H7 += h;
        } 
    }
}