/// <summary>
/// Masks an option (i.e., a sender input message).
/// </summary>
/// <remarks>
/// The option is XOR-masked with the output of a random oracle queried with the
/// concatenation of the binary representations of the given groupElement, invocationIndex and optionIndex.
/// </remarks>
/// <param name="option">The sender input/option to be masked.</param>
/// <param name="groupElement">The group element that acts as "key" in the query to the random oracle.</param>
/// <param name="invocationIndex">The index of the OT invocation this option belongs to.</param>
/// <param name="optionIndex">The index of the option.</param>
/// <returns>The masked option.</returns>
private byte[] MaskOption(byte[] option, BigInteger groupElement, int invocationIndex, int optionIndex)
{
using (RandomOracle randomOracle = _randomOracleProvider.Create())
{
byte[] query = BufferBuilder.From(groupElement.ToByteArray()).With(invocationIndex).With(optionIndex).Create();
return(randomOracle.Mask(option, query));
}
}
public NaorPinkasObliviousTransfer(SecurityParameters parameters, CryptoContext cryptoContext)
{
_parameters = parameters;
_randomOracle = new HashRandomOracle(cryptoContext.HashAlgorithm);
_randomNumberGenerator = new ThreadsafeRandomNumberGenerator(cryptoContext.RandomNumberGenerator);
#if DEBUG
Console.WriteLine("Security parameters:");
Console.WriteLine("p = {0}", _parameters.P);
Console.WriteLine("q = {0}", _parameters.Q);
Console.WriteLine("g = {0}", _parameters.G);
Console.WriteLine("group element size = {0} bytes", _parameters.GroupElementSize);
Console.WriteLine("exponent size = {0} bytes", _parameters.ExponentSize);
#endif
}