utility functions for filename nonces

00_hash_naming.cs

byte[] Sha256(string s)
{
    using (var hash = SHA256.Create())
    {
        return hash.ComputeHash(Encoding.UTF8.GetBytes(s));
    }
}

byte[] Fold(byte[] input)
{
    if (input.Length == 0) return new byte[0];
    if (input.Length % 2 == 1)
    {
        throw Exceptions.IllegalArgument("input", "an even length");
    }
    int length = input.Length / 2;
    byte[] output = new byte[length];

    for (int i=0; i<length; i++)
    {
        output[i] = (byte)(input[i] ^ input[i + length]);
    }
    return output;
}

string Base64Encode(byte[] b)
{
    return System.Convert.ToBase64String(b);
}

01_usage.cs

void usage() {
    var hash = Sha256("hello");
    var shortened = Fold(hash);
    var encoded = Base64Encode(shortened);
}