/// <summary>
/// Receives and returns the matrix Q as specified in the OT extension protocol of Ishai et al.
///
/// This is involves the preprocessing (expanding the base OTs for the number of invocations, etc..)
/// for all variants of the OT extension. This method should be called is the first step by
/// subclasses implementing the OT extension variants.
/// </summary>
/// <param name="numberOfInvocations">The number of invocations/instances of OT.</param>
/// <returns>The matrix Q of correlated randomness.</returns>
protected async Task <BitMatrix> ReceiveQMatrix(int numberOfInvocations)
{
if (_senderState.SeededRandomOracles == null)
{
await ExecuteSenderBaseOTAsync();
}
int numberOfRandomBytes = BitArray.RequiredBytes(numberOfInvocations);
BitMatrix q = new BitMatrix((uint)numberOfInvocations, (uint)SecurityParameter);
// note(lumip): could precompute the masks for the response to have only cheap Xor after
// waiting for the message, but not sure if it really is a significant performance issue
// todo(lumip): should try-catch in case random oracle runs out
// and ideally performs new base OTs and repeat
byte[][][] qOTResult = await CommunicationTools.ReadOptionsAsync(Channel, 1, SecurityParameter, numberOfRandomBytes);
Debug.Assert(qOTResult.Length == SecurityParameter);
PairIndexArray randomChoiceInts = _senderState.RandomChoices.ToPairIndexArray();
Parallel.For(0, SecurityParameter, k =>
{
Debug.Assert(qOTResult[k].Length == 1);
Debug.Assert(qOTResult[k][0].Length == numberOfRandomBytes);
BitArray mask = BitArray.FromBytes(
_senderState.SeededRandomOracles[k].Take(numberOfRandomBytes).ToArray(),
numberOfInvocations
);
int s = randomChoiceInts[k];
BitArray qColumn = mask;
if (s == 1)
{
qColumn.Xor(BitArray.FromBytes(qOTResult[k][0], numberOfInvocations));
}
q.SetColumn((uint)k, qColumn);
});
return(q);
}
public PairIndexArray ToPairIndexArray()
{
return(PairIndexArray.FromBytes(ToBytes(), Length));
}
public static BitArray FromPairIndexArray(PairIndexArray array)
{
return(new BitArray(array.ToBytes(), array.Length));
}
public Task <byte[][]> ReceiveAsync(PairIndexArray selectionIndices, int numberOfInvocations, int numberOfMessageBytes)
{
return(ReceiveAsync(BitArray.FromPairIndexArray(selectionIndices), numberOfInvocations, numberOfMessageBytes));
}