// This is an implementation of
// http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf

namespace Tiobon.Core.Common.Helper;

using Word32 = System.UInt32;
using Word64 = System.UInt64;


public static class ShaHelper
{
    // Constants K
    static Word32[] K1;
    static Word32[] K256;
    static Word64[] K512;

    // Initial hash values H0
    static Word32[] H0Sha1;
    static Word32[] H0Sha224;
    static Word32[] H0Sha256;
    static Word64[] H0Sha384;
    static Word64[] H0Sha512;
    static Word64[] H0Sha512_224;
    static Word64[] H0Sha512_256;


    static ShaHelper()
    {
        DefineK1();
        DefineK256();
        DefineK512();

        DefineH0Sha1();
        DefineH0Sha224();
        DefineH0Sha256();
        DefineH0Sha384();
        DefineH0Sha512();
        DefineH0Sha512_224();
        DefineH0Sha512_256();
    }


    #region Public Functions

    public static byte[] Sha1(byte[] plaintext)
    {
        DefineH0Sha1();
        return Sha1Algorithm(plaintext);
    }

    public static string Sha1(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha1(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha224(byte[] plaintext)
    {
        DefineH0Sha224();
        return Sha256Algorithm(plaintext, H0Sha224, 224);
    }

    public static string Sha224(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha224(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha256(byte[] plaintext)
    {
        DefineH0Sha256();
        return Sha256Algorithm(plaintext, H0Sha256, 256);
    }

    public static string Sha256(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha256(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha512(byte[] plaintext)
    {
        DefineH0Sha512();
        return Sha512Algorithm(plaintext, H0Sha512, 512);
    }

    public static string Sha512(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha512(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha384(byte[] plaintext)
    {
        DefineH0Sha384();
        return Sha512Algorithm(plaintext, H0Sha384, 384);
    }

    public static string Sha384(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha384(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha512_224(byte[] plaintext)
    {
        DefineH0Sha512_224();
        return Sha512Algorithm(plaintext, H0Sha512_224, 224);
    }

    public static string Sha512_224(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha512_224(ShaUtilities.StringToByteArray(plaintext)));
    }

    public static byte[] Sha512_256(byte[] plaintext)
    {
        DefineH0Sha512_256();
        return Sha512Algorithm(plaintext, H0Sha512_256, 256);
    }

    public static string Sha512_256(string plaintext)
    {
        return ShaUtilities.ByteArrayToHexString(Sha512_256(ShaUtilities.StringToByteArray(plaintext)));
    }

    #endregion





    #region Hash Algorithms

    static Word32[] CreateMessageScheduleSha1(Block512 block)
    {
        // The message schedule.
        Word32[] W = new Word32[80];

        // Prepare the message schedule W.
        // The first 16 words in W are the same as the words of the block.
        // The remaining 80-16 = 64 words in W are functions of the previously defined words. 
        for (int t = 0; t < 80; t++)
        {
            if (t < 16)
            {
                W[t] = block.words[t];
            }
            else
            {
                W[t] = RotL(1, W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16]);
            }
        }

        return W;
    }

    static Word32[] CreateMessageScheduleSha256(Block512 block)
    {
        // The message schedule.
        Word32[] W = new Word32[64];

        // Prepare the message schedule W.
        // The first 16 words in W are the same as the words of the block.
        // The remaining 64-16 = 48 words in W are functions of the previously defined words. 
        for (int t = 0; t < 64; t++)
        {
            if (t < 16)
            {
                W[t] = block.words[t];
            }
            else
            {
                W[t] = sigma1_256(W[t - 2]) + W[t - 7] + sigma0_256(W[t - 15]) + W[t - 16];
            }
        }

        return W;
    }

    static Word64[] CreateMessageScheduleSha512(Block1024 block)
    {
        // The message schedule.
        Word64[] W = new Word64[80];

        // Prepare the message schedule W.
        // The first 16 words in W are the same as the words of the block.
        // The remaining 80-16 =64 words in W are functions of the previously defined words. 
        for (int t = 0; t < 80; t++)
        {
            if (t < 16)
            {
                W[t] = block.words[t];
            }
            else
            {
                W[t] = sigma1_512(W[t - 2]) + W[t - 7] + sigma0_512(W[t - 15]) + W[t - 16];
            }
        }

        return W;
    }

    static byte[] Sha1Algorithm(byte[] plaintext)
    {
        Block512[] blocks = ConvertPaddedTextToBlock512Array(PadPlainText512(plaintext));

        // Define the hash variable and set its initial values.
        Word32[] H = new Word32[5];
        H0Sha1.CopyTo(H, 0);

        for (int i = 0; i < blocks.Length; i++)
        {
            Word32[] W = CreateMessageScheduleSha1(blocks[i]);

            // Set the working variables a,...,e to the current hash values.
            Word32 a = H[0];
            Word32 b = H[1];
            Word32 c = H[2];
            Word32 d = H[3];
            Word32 e = H[4];

            for (int t = 0; t < 80; t++)
            {
                Word32 T = RotL(5, a) + f(t, b, c, d) + e + K1[t] + W[t];
                e = d;
                d = c;
                c = RotL(30, b);
                b = a;
                a = T;
            }

            // Update the current value of the hash H after processing block i.
            H[0] += a;
            H[1] += b;
            H[2] += c;
            H[3] += d;
            H[4] += e;
        }

        // Concatenating the final 5 hash words H[0],...,H[4] gives the digest.
        // Since each H[i] is 4 bytes, the digest is 5 * 4 = 20 bytes = 160 bits.
        return ShaUtilities.Word32ArrayToByteArray(H);
    }

    static byte[] Sha256Algorithm(byte[] plaintext, Word32[] H0, int numberBits)
    {
        Block512[] blocks = ConvertPaddedTextToBlock512Array(PadPlainText512(plaintext));

        // Define the hash variables and set their initial values.
        Word32[] H = H0;

        for (int i = 0; i < blocks.Length; i++)
        {
            Word32[] W = CreateMessageScheduleSha256(blocks[i]);

            // Set the working variables a,...,h to the current hash values.
            Word32 a = H[0];
            Word32 b = H[1];
            Word32 c = H[2];
            Word32 d = H[3];
            Word32 e = H[4];
            Word32 f = H[5];
            Word32 g = H[6];
            Word32 h = H[7];

            for (int t = 0; t < 64; t++)
            {
                Word32 T1 = h + Sigma1_256(e) + Ch(e, f, g) + K256[t] + W[t];
                Word32 T2 = Sigma0_256(a) + Maj(a, b, c);
                h = g;
                g = f;
                f = e;
                e = d + T1;
                d = c;
                c = b;
                b = a;
                a = T1 + T2;
            }

            // Update the current value of the hash H after processing block i.
            H[0] += a;
            H[1] += b;
            H[2] += c;
            H[3] += d;
            H[4] += e;
            H[5] += f;
            H[6] += g;
            H[7] += h;
        }

        // Concatenate all the Word32 Hash Values
        byte[] hash = ShaUtilities.Word32ArrayToByteArray(H);

        // The number of bytes in the final output hash 
        int numberBytes = numberBits / 8;
        byte[] truncatedHash = new byte[numberBytes];
        Array.Copy(hash, truncatedHash, numberBytes);

        return truncatedHash;
    }

    static byte[] Sha512Algorithm(byte[] plaintext, Word64[] H0, int numberBits)
    {
        Block1024[] blocks = ConvertPaddedMessageToBlock1024Array(PadPlainText1024(plaintext));

        // Define the hash variable and set its initial values.
        Word64[] H = H0;

        for (int i = 0; i < blocks.Length; i++)
        {
            Word64[] W = CreateMessageScheduleSha512(blocks[i]);

            // Set the working variables a,...,h to the current hash values.
            Word64 a = H[0];
            Word64 b = H[1];
            Word64 c = H[2];
            Word64 d = H[3];
            Word64 e = H[4];
            Word64 f = H[5];
            Word64 g = H[6];
            Word64 h = H[7];

            for (int t = 0; t < 80; t++)
            {
                Word64 T1 = h + Sigma1_512(e) + Ch(e, f, g) + K512[t] + W[t];
                Word64 T2 = Sigma0_512(a) + Maj(a, b, c);
                h = g;
                g = f;
                f = e;
                e = d + T1;
                d = c;
                c = b;
                b = a;
                a = T1 + T2;
            }

            // Update the current value of the hash H after processing block i.
            H[0] += a;
            H[1] += b;
            H[2] += c;
            H[3] += d;
            H[4] += e;
            H[5] += f;
            H[6] += g;
            H[7] += h;
        }

        // Concatenate all the Word64 Hash Values
        byte[] hash = ShaUtilities.Word64ArrayToByteArray(H);

        // The number of bytes in the final output hash 
        int numberBytes = numberBits / 8;
        byte[] truncatedHash = new byte[numberBytes];
        Array.Copy(hash, truncatedHash, numberBytes);

        return truncatedHash;
    }

    #endregion


    #region Plaintext preprocessing functions

    static byte[] PadPlainText512(byte[] plaintext)
    {
        // After padding the total bits of the output will be divisible by 512.
        int numberBits = plaintext.Length * 8;
        int t = (numberBits + 8 + 64) / 512;

        // Note that 512 * (t + 1) is the least multiple of 512 greater than (numberBits + 8 + 64)
        // Therefore the number of zero bits we need to add is
        int k = 512 * (t + 1) - (numberBits + 8 + 64);

        // Since numberBits % 8 = 0, we know k % 8 = 0. So n = k / 8 is the number of zero bytes to add.
        int n = k / 8;

        List<byte> paddedtext = plaintext.ToList();

        // Start the padding by concatenating 1000_0000 = 0x80 = 128
        paddedtext.Add(0x80);

        // Next add n zero bytes
        for (int i = 0; i < n; i++)
        {
            paddedtext.Add(0);
        }

        // Now add 8 bytes (64 bits) to represent the length of the message in bits
        byte[] B = BitConverter.GetBytes((ulong)numberBits);
        Array.Reverse(B);

        for (int i = 0; i < B.Length; i++)
        {
            paddedtext.Add(B[i]);
        }

        return paddedtext.ToArray();
    }

    static byte[] PadPlainText1024(byte[] plaintext)
    {
        // After padding the total bits of the output will be divisible by 1024.
        int numberBits = plaintext.Length * 8;
        int t = (numberBits + 8 + 128) / 1024;

        // Note that 1024 * (t + 1) is the least multiple of 1024 greater than (numberBits + 8 + 128)
        // Therefore the number of zero bits we need to add is
        int k = 1024 * (t + 1) - (numberBits + 8 + 128);

        // Since numberBits % 8 = 0, we know k % 8 = 0. So n = k / 8 is the number of zero bytes to add.
        int n = k / 8;

        List<byte> paddedtext = plaintext.ToList();

        // Start the padding by concatenating 1000_0000 = 0x80 = 128
        paddedtext.Add(0x80);

        // Next add n zero bytes
        for (int i = 0; i < n; i++)
        {
            paddedtext.Add(0);
        }

        // Now add 16 bytes (128 bits) to represent the length of the message in bits.
        // C# does not have 128 bit integer.
        // For now just add 8 zero bytes and then 8 bytes to represent the int
        for (int i = 0; i < 8; i++)
        {
            paddedtext.Add(0);
        }

        byte[] B = BitConverter.GetBytes((ulong)numberBits);
        Array.Reverse(B);

        for (int i = 0; i < B.Length; i++)
        {
            paddedtext.Add(B[i]);
        }

        return paddedtext.ToArray();
    }

    static Block512[] ConvertPaddedTextToBlock512Array(byte[] paddedtext)
    {
        // We are assuming M has been padded, so the number of bits in M is divisible by 512 
        int numberBlocks = (paddedtext.Length * 8) / 512;  // same as: paddedtext.Length / 64
        Block512[] blocks = new Block512[numberBlocks];

        for (int i = 0; i < numberBlocks; i++)
        {
            // First extract the relavant subarray from paddedtext
            byte[] B = new byte[64]; // 64 * 8 = 512

            for (int j = 0; j < 64; j++)
            {
                B[j] = paddedtext[i * 64 + j];
            }

            Word32[] words = ShaUtilities.ByteArrayToWord32Array(B);
            blocks[i] = new Block512(words);
        }

        return blocks;
    }

    static Block1024[] ConvertPaddedMessageToBlock1024Array(byte[] M)
    {
        // We are assuming M is padded, so the number of bits in M is divisible by 1024 
        int numberBlocks = (M.Length * 8) / 1024;  // same as: M.Length / 128
        Block1024[] blocks = new Block1024[numberBlocks];

        for (int i = 0; i < numberBlocks; i++)
        {
            // First extract the relavant subarray from M
            byte[] B = new byte[128]; // 128 * 8 = 1024

            for (int j = 0; j < 128; j++)
            {
                B[j] = M[i * 128 + j];
            }

            Word64[] words = ShaUtilities.ByteArrayToWord64Array(B);
            blocks[i] = new Block1024(words);
        }

        return blocks;
    }


    #endregion



    #region Functions used in the hashing process.

    // Most of these functions have a Word32 version and a Word64 version.
    // Sometimes they are the same (Ch, Maj,..) but sometimes different (Sigma0_256, Sigma0_512).
    // We do not need a RotL or Parity function for Word64 since they are only used in Sha-1.

    static Word32 ShR(int n, Word32 x)
    {
        // should have 0 <= n < 32
        return (x >> n);
    }

    static Word64 ShR(int n, Word64 x)
    {
        // should have 0 <= n < 64
        return (x >> n);
    }

    static Word32 RotR(int n, Word32 x)
    {
        // should have 0 <= n < 32
        return (x >> n) | (x << 32 - n);
    }

    static Word64 RotR(int n, Word64 x)
    {
        // should have 0 <= n < 64
        return (x >> n) | (x << 64 - n);
    }

    static Word32 RotL(int n, Word32 x)
    {
        // should have 0 <= n < 32
        return (x << n) | (x >> 32 - n);
    }

    static Word32 Ch(Word32 x, Word32 y, Word32 z)
    {
        return (x & y) ^ (~x & z);
    }

    static Word64 Ch(Word64 x, Word64 y, Word64 z)
    {
        return (x & y) ^ (~x & z);
    }

    static Word32 Maj(Word32 x, Word32 y, Word32 z)
    {
        return (x & y) ^ (x & z) ^ (y & z);
    }

    static Word64 Maj(Word64 x, Word64 y, Word64 z)
    {
        return (x & y) ^ (x & z) ^ (y & z);
    }

    static Word32 Parity(Word32 x, Word32 y, Word32 z)
    {
        return x ^ y ^ z;
    }

    static Word32 f(int t, Word32 x, Word32 y, Word32 z)
    {
        // This function is used in Sha-1
        // should have 0 <= t <= 79

        if (t >= 0 && t <= 19)
        {
            return Ch(x, y, z);
        }
        else if (t >= 20 && t <= 39)
        {
            return Parity(x, y, z);
        }
        else if (t >= 40 && t <= 59)
        {
            return Maj(x, y, z);
        }
        else if (t >= 60 && t <= 79)
        {
            return Parity(x, y, z);
        }
        else
        {
            throw new ArgumentException("ERROR: t is out of bounds");
        }
    }

    static Word32 Sigma0_256(Word32 x)
    {
        return RotR(2, x) ^ RotR(13, x) ^ RotR(22, x);
    }

    static Word32 Sigma1_256(Word32 x)
    {
        return RotR(6, x) ^ RotR(11, x) ^ RotR(25, x);
    }

    static Word32 sigma0_256(Word32 x)
    {
        return RotR(7, x) ^ RotR(18, x) ^ ShR(3, x);
    }

    static Word32 sigma1_256(Word32 x)
    {
        return RotR(17, x) ^ RotR(19, x) ^ ShR(10, x);
    }

    static Word64 Sigma0_512(Word64 x)
    {
        return RotR(28, x) ^ RotR(34, x) ^ RotR(39, x);
    }

    static Word64 Sigma1_512(Word64 x)
    {
        return RotR(14, x) ^ RotR(18, x) ^ RotR(41, x);
    }

    static Word64 sigma0_512(Word64 x)
    {
        return RotR(1, x) ^ RotR(8, x) ^ ShR(7, x);
    }

    static Word64 sigma1_512(Word64 x)
    {
        return RotR(19, x) ^ RotR(61, x) ^ ShR(6, x);
    }

    #endregion



    #region Functions to define the constants K and the initial hashes H0.

    static void DefineK1()
    {
        // The eighty 32-bit words in the array K1 are used in Sha-1.

        K1 = new Word32[80];

        for (int i = 0; i < 80; i++)
        {
            if (i <= 19)
            {
                K1[i] = 0x5a827999;
            }
            else if (i <= 39)
            {
                K1[i] = 0x6ed9eba1;
            }
            else if (i <= 59)
            {
                K1[i] = 0x8f1bbcdc;
            }
            else
            {
                K1[i] = 0xca62c1d6;
            }
        }
    }

    static void DefineK256()
    {
        // The sixty four 32-bit words in the array K256 are used in Sha-224 and Sha-256. 
        // They are obtained by taking the first 32 bits of the fractional
        // parts of the cube roots of the first sixty four primes. 
        // -------------------------------------------------------
        // NOTE: To find the first 32 bits of the fractional part of the cube root of an integer n:
        // double x = Math.Pow(n, 1d / 3);
        // x = x - Math.Floor(x);
        // x = x * Math.Pow(2, 32);
        // return (uint)x;

        K256 = new Word32[]
        {
            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
        };
    }

    static void DefineK512()
    {
        // The eighty 64-bit words in the array K512 are used in Sha-384, Sha-512, Sha-512/224, Sha-512/256. 
        // They are obtained by taking the first 64 bits of the fractional
        // parts of the cube roots of the first eighty primes. 

        K512 = new Word64[]
        {
            0x428a2f98d728ae22, 0x7137449123ef65cd, 0xb5c0fbcfec4d3b2f, 0xe9b5dba58189dbbc,
            0x3956c25bf348b538, 0x59f111f1b605d019, 0x923f82a4af194f9b, 0xab1c5ed5da6d8118,
            0xd807aa98a3030242, 0x12835b0145706fbe, 0x243185be4ee4b28c, 0x550c7dc3d5ffb4e2,
            0x72be5d74f27b896f, 0x80deb1fe3b1696b1, 0x9bdc06a725c71235, 0xc19bf174cf692694,
            0xe49b69c19ef14ad2, 0xefbe4786384f25e3, 0x0fc19dc68b8cd5b5, 0x240ca1cc77ac9c65,
            0x2de92c6f592b0275, 0x4a7484aa6ea6e483, 0x5cb0a9dcbd41fbd4, 0x76f988da831153b5,
            0x983e5152ee66dfab, 0xa831c66d2db43210, 0xb00327c898fb213f, 0xbf597fc7beef0ee4,
            0xc6e00bf33da88fc2, 0xd5a79147930aa725, 0x06ca6351e003826f, 0x142929670a0e6e70,
            0x27b70a8546d22ffc, 0x2e1b21385c26c926, 0x4d2c6dfc5ac42aed, 0x53380d139d95b3df,
            0x650a73548baf63de, 0x766a0abb3c77b2a8, 0x81c2c92e47edaee6, 0x92722c851482353b,
            0xa2bfe8a14cf10364, 0xa81a664bbc423001, 0xc24b8b70d0f89791, 0xc76c51a30654be30,
            0xd192e819d6ef5218, 0xd69906245565a910, 0xf40e35855771202a, 0x106aa07032bbd1b8,
            0x19a4c116b8d2d0c8, 0x1e376c085141ab53, 0x2748774cdf8eeb99, 0x34b0bcb5e19b48a8,
            0x391c0cb3c5c95a63, 0x4ed8aa4ae3418acb, 0x5b9cca4f7763e373, 0x682e6ff3d6b2b8a3,
            0x748f82ee5defb2fc, 0x78a5636f43172f60, 0x84c87814a1f0ab72, 0x8cc702081a6439ec,
            0x90befffa23631e28, 0xa4506cebde82bde9, 0xbef9a3f7b2c67915, 0xc67178f2e372532b,
            0xca273eceea26619c, 0xd186b8c721c0c207, 0xeada7dd6cde0eb1e, 0xf57d4f7fee6ed178,
            0x06f067aa72176fba, 0x0a637dc5a2c898a6, 0x113f9804bef90dae, 0x1b710b35131c471b,
            0x28db77f523047d84, 0x32caab7b40c72493, 0x3c9ebe0a15c9bebc, 0x431d67c49c100d4c,
            0x4cc5d4becb3e42b6, 0x597f299cfc657e2a, 0x5fcb6fab3ad6faec, 0x6c44198c4a475817
        };
    }

    static void DefineH0Sha1()
    {
        H0Sha1 = new Word32[]
        {
            0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0xc3d2e1f0
        };
    }

    static void DefineH0Sha224()
    {
        H0Sha224 = new Word32[]
        {
            0xc1059ed8, 0x367cd507, 0x3070dd17, 0xf70e5939,
            0xffc00b31, 0x68581511, 0x64f98fa7, 0xbefa4fa4
        };

    }

    static void DefineH0Sha256()
    {
        // These eight 32-bit words are obtained by taking the first 32 bits of the 
        // fractional parts of the square roots of the first 8 prime numbers. 

        H0Sha256 = new Word32[]
        {
            0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
            0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
        };
    }

    static void DefineH0Sha384()
    {
        // These eight 64-bit words are obtained by taking the first 64 bits of the 
        // fractional parts of the square roots of the ninth through sixteenth prime numbers.

        H0Sha384 = new Word64[]
        {
            0xcbbb9d5dc1059ed8, 0x629a292a367cd507, 0x9159015a3070dd17, 0x152fecd8f70e5939,
            0x67332667ffc00b31, 0x8eb44a8768581511, 0xdb0c2e0d64f98fa7, 0x47b5481dbefa4fa4
        };
    }

    static void DefineH0Sha512()
    {
        // These eight 64-bit words are obtained by taking the first 64 bits of the 
        // fractional parts of the square roots of the first eight prime numbers.

        H0Sha512 = new Word64[]
        {
            0x6a09e667f3bcc908, 0xbb67ae8584caa73b, 0x3c6ef372fe94f82b, 0xa54ff53a5f1d36f1,
            0x510e527fade682d1, 0x9b05688c2b3e6c1f, 0x1f83d9abfb41bd6b, 0x5be0cd19137e2179
        };
    }

    static void DefineH0Sha512_224()
    {
        // These eight 64-bit words are obtained from GenerateInitialHashSha512t(224)

        H0Sha512_224 = new Word64[]
        {
            0x8c3d37c819544da2, 0x73e1996689dcd4d6, 0x1dfab7ae32ff9c82, 0x679dd514582f9fcf,
            0x0f6d2b697bd44da8, 0x77e36f7304c48942, 0x3f9d85a86a1d36c8, 0x1112e6ad91d692a1
        };
    }

    static void DefineH0Sha512_256()
    {
        // These eight 64-bit words are obtained from GenerateInitialHashSha512t(256)

        H0Sha512_256 = new Word64[]
        {
            0x22312194fc2bf72c, 0x9f555fa3c84c64c2, 0x2393b86b6f53b151, 0x963877195940eabd,
            0x96283ee2a88effe3, 0xbe5e1e2553863992, 0x2b0199fc2c85b8aa, 0x0eb72ddc81c52ca2
        };
    }

    /*
    static Word64[] GenerateInitialHashSha512t(int t)
    {
        // t = number of bits.
        // We assume t is postive, divisible by 8 and is strictly less than 512. 
        // Also assume numberBits != 384 (WHY does 384 get its own initial hash?) 

        Word64[] H0 = new Word64[8];

        for (int i = 0; i < 8; i++)
        {
            H0[i] = H0Sha512[i] ^ 0xa5a5a5a5a5a5a5a5;
        }

        byte[] B = ShaUtil.StringToByteArray("SHA-512/" + t.ToString());  // so arbitary!

        return ShaUtil.ByteArrayToWord64Array(Sha512(B)); ;
    }
    */

    #endregion

}


// Helper Classes

class Block512
{
    // A Block512 consists of an array of 16 elements of type Word32.
    public Word32[] words;

    public Block512(Word32[] words)
    {
        if (words.Length == 16)
        {
            this.words = words;
        }
        else
        {
            Console.WriteLine("ERROR: A block must be 16 words");
            this.words = null;
        }
    }
}


class Block1024
{
    // A Block1024 consists of an array of 16 elements of type Word64.
    public Word64[] words;

    public Block1024(Word64[] words)
    {
        if (words.Length == 16)
        {
            this.words = words;
        }
        else
        {
            Console.WriteLine("ERROR: A block must be 16 words");
            this.words = null;
        }
    }
}


static class ShaUtilities
{
    #region Functions to convert between byte arrays and Word32 arrays, and Word64 arrays.

    public static bool ByteArraysEqual(byte[] B1, byte[] B2)
    {
        if ((B1 == null) && (B2 == null))
            return true;

        if ((B1 == null) || (B2 == null))
            return false;

        if (B1.Length != B2.Length)
            return false;

        for (int i = 0; i < B1.Length; i++)
        {
            if (B1[i] != B2[i])
                return false;
        }

        return true;
    }

    public static byte[] StringToByteArray(string plaintext)
    {
        char[] c = plaintext.ToCharArray();
        int numberBytes = plaintext.Length;
        byte[] b = new byte[numberBytes];

        for (int i = 0; i < numberBytes; i++)
        {
            b[i] = Convert.ToByte(c[i]);
        }

        return b;
    }

    // Returns an array of 4 bytes.
    public static byte[] Word32ToByteArray(Word32 x)
    {
        byte[] b = BitConverter.GetBytes(x);
        Array.Reverse(b);
        return b;
    }

    // Returns an array of 8 bytes.
    public static byte[] Word64ToByteArray(Word64 x)
    {
        byte[] b = BitConverter.GetBytes(x);
        Array.Reverse(b);
        return b;
    }

    public static byte[] Word32ArrayToByteArray(Word32[] words)
    {
        List<byte> b = new List<byte>();

        for (int i = 0; i < words.Length; i++)
        {
            b.AddRange(Word32ToByteArray(words[i]));
        }

        return b.ToArray();
    }

    public static byte[] Word32ArrayToByteArray(Word32[] words, int startIndex, int numberWords)
    {
        // This overload is useful in Sha224 
        // assume 0 <= startIndex < words.Length and startIndex + numberWords <= words.Length

        List<byte> b = new List<byte>();

        for (int i = startIndex; i < startIndex + numberWords; i++)
        {
            b.AddRange(Word32ToByteArray(words[i]));
        }

        return b.ToArray();
    }

    public static byte[] Word64ArrayToByteArray(Word64[] words)
    {
        List<byte> b = new List<byte>();

        for (int i = 0; i < words.Length; i++)
        {
            b.AddRange(Word64ToByteArray(words[i]));
        }

        return b.ToArray();
    }

    public static Word32 ByteArrayToWord32(byte[] B, int startIndex)
    {
        // We assume: 0 <= startIndex < B. Length, and startIndex + 4 <= B.Length

        Word32 c = 256;
        Word32 output = 0;

        for (int i = startIndex; i < startIndex + 4; i++)
        {
            output = output * c + (Word32)B[i];
        }

        return output;
    }

    public static Word64 ByteArrayToWord64(byte[] B, int startIndex)
    {
        // We assume: 0 <= startIndex < B. Length, and startIndex + 8 <= B.Length
        Word64 c = 256;
        Word64 output = 0;

        for (int i = startIndex; i < startIndex + 8; i++)
        {
            output = output * c + B[i];
        }

        return output;
    }

    public static Word32[] ByteArrayToWord32Array(byte[] B)
    {
        // We assume B is not null, is not empty and number elements is divisible by 4
        int numberBytes = B.Length;
        int n = numberBytes / 4; // 4 bytes for each Word32
        Word32[] word32Array = new Word32[n];

        for (int i = 0; i < n; i++)
        {
            word32Array[i] = ByteArrayToWord32(B, 4 * i);
        }

        return word32Array;
    }


    public static Word64[] ByteArrayToWord64Array(byte[] B)
    {
        // We assume B is not null, is not empty and number elements is divisible by 8
        int numberWords = B.Length / 8; // 8 bytes for each Word32
        Word64[] word64Array = new Word64[numberWords];

        for (int i = 0; i < numberWords; i++)
        {
            word64Array[i] = ByteArrayToWord64(B, 8 * i);
        }

        return word64Array;
    }

    #endregion


    #region To string methods

    public static string ByteToBinaryString(byte b)
    {
        string binaryString = Convert.ToString(b, 2).PadLeft(8, '0');
        return binaryString.Substring(0, 4) + "_" + binaryString.Substring(4, 4);
    }

    public static string ByteArrayToBinaryString(byte[] x)
    {
        string binaryString = "";

        for (int i = 0; i < x.Length; i++)
        {
            binaryString += ByteToBinaryString(x[i]);

            if (i < x.Length - 1)
            {
                binaryString += "  ";
            }
        }

        return binaryString;
    }

    public static string ByteToHexString(byte b)
    {
        return Convert.ToString(b, 16).PadLeft(2, '0');
    }

    public static string ByteArrayToHexString(byte[] a)
    {
        string hexString = "";

        for (int i = 0; i < a.Length; i++)
        {
            hexString += ByteToHexString(a[i]);
        }

        return hexString;
    }

    public static string Word32ToBinaryString(Word32 x)
    {
        return ByteArrayToBinaryString(Word32ToByteArray(x));
    }

    public static string Word32ToHexString(Word32 x)
    {
        return ByteArrayToHexString(Word32ToByteArray(x));
    }

    public static string Word64ToHexString(Word64 x)
    {
        return ByteArrayToHexString(Word64ToByteArray(x));
    }

    public static string ByteArrayToString(byte[] X)
    {
        if (X == null)
        {
            Console.WriteLine("ERROR: The byte array is null");
            return null;
        }

        string s = "";

        for (int i = 0; i < X.Length; i++)
        {
            s += (char)X[i];
        }

        return s;
    }

    #endregion
}





