Try entering HMAC-SHA256 code with C # .Net

Question

I am trying to code the HMAC-SHA256 algorithm as a function

HMAC (K, m) = H ((K ⊕ opad) ∥ H ((K ⊕ ipad) ∥ m))

Where

• H is a cryptographic hash function,
• K is the secret key, padded on the right, with additional zeros for the size of the input block of the hash function or a hash of the source code if it is longer than this block size,
• m is an authentication message,
• ∥ stands for concatenation,
• ⊕ stands for exceptional or (XOR),
• opad is an external complement (0x5c5c5c ... 5c5c, single-frame hexadecimal constant),
• ipad - internal padding (0x363636 ... 3636, single-frame hexadecimal constant).

and this code

public static string MyHMACHash(string key , string message)
{
    Encoding encoding = Encoding.UTF8;
    //var md = System.Security.Cryptography.MD5CryptoServiceProvider.Create();
    SHA256 hash = SHA256Managed.Create();
    byte[] trans_5C = new byte[32];
    byte[] trans_36 = new byte[32];

    byte[] b_key = encoding.GetBytes(key);
    // TODO: also check if key is to short
    if (b_key.Length > 32)
        b_key = hash.ComputeHash(b_key);

    for (int i = 0; i < 32; i++)
    {
        trans_5C[i] = 92;
        trans_36[i] = 54;
        if (i < key.Length)
        {
            trans_5C[i] ^= b_key[i];
            trans_36[i] ^= b_key[i];
        }
    }

    byte[] inner = hash.ComputeHash(trans_36.Concat(encoding.GetBytes(message)).ToArray());
    var Fhash = hash.ComputeHash(trans_5C.Concat(inner).ToArray());

    StringBuilder sb = new StringBuilder();
    foreach (byte b in Fhash)
        sb.Append(b.ToString("x2"));

    string result = sb.ToString(); // = 9036a1a3f654aefeab426e9f7e17288e
    return result;
}

, HMAC-SHA256 -

Answer 1

HMAC. , , , K, -; . SHA256 64 . , 32 . : http://en.wikipedia.org/wiki/Secure_Hash_Algorithm.

public static string MyHMACHash(string key, string message)
{
    Encoding encoding = Encoding.UTF8;

    //Reference http://en.wikipedia.org/wiki/Secure_Hash_Algorithm
    //SHA256 block size is 512 bits => 64 bytes.
    const int HashBlockSize = 64;

    var keyBytes = encoding.GetBytes(key);
    var opadKeySet = new byte[HashBlockSize];
    var ipadKeySet = new byte[HashBlockSize];


    if (keyBytes.Length > HashBlockSize)
    {
        keyBytes = GetHash(keyBytes);
    }

    // This condition is independent of previous
    // condition. If previous was true
    // we still need to execute this to make keyBytes same length
    // as blocksize with 0 padded if its less than block size
    if (keyBytes.Length < HashBlockSize)
    {
        var newKeyBytes = new byte[HashBlockSize];
        keyBytes.CopyTo(newKeyBytes, 0);
        keyBytes = newKeyBytes;
    }


    for (int i = 0; i < keyBytes.Length; i++)
    {
        opadKeySet[i] = (byte)(keyBytes[i] ^ 0x5C);
        ipadKeySet[i] = (byte)(keyBytes[i] ^ 0x36);
    }

    var hash = GetHash(ByteConcat(opadKeySet, 
        GetHash(ByteConcat(ipadKeySet, encoding.GetBytes(message)))));

    // Convert to standard hex string 
    return hash.Select<byte, string>(a => a.ToString("x2"))
                .Aggregate<string>((a, b) => string.Format("{0}{1}", a, b));            
}

public static byte[] GetHash(byte[] bytes)
{
    using (var hash = new SHA256Managed())
    {
        return hash.ComputeHash(bytes);
    }
}

public static byte[] ByteConcat(byte[] left, byte[] right)
{
    if (null == left)
    {
        return right;
    }

    if (null == right)
    {
        return left;
    }

    byte[] newBytes = new byte[left.Length + right.Length];
    left.CopyTo(newBytes, 0);
    right.CopyTo(newBytes, left.Length);

    return newBytes;
}