}// DeriveKey()
internal static void DeriveKey(HMAC keyedHmac, ArraySegment<byte> bufferSegment, ArraySegment<byte> derivedOutput, uint counter = 1)
{
int derivedOutputCount = derivedOutput.Count, derivedOutputOffset = derivedOutput.Offset;
byte[] K_i = null;
HMAC2 keyedHmac2 = keyedHmac as HMAC2;
checked
{
// Calculate each K_i value and copy the leftmost bits to the output buffer as appropriate.
for (var counterStruct = new Utils.IntStruct { UintValue = counter }; derivedOutputCount > 0; ++counterStruct.UintValue)
{
counterStruct.ToBEBytes(bufferSegment.Array, bufferSegment.Offset); // update the counter within the buffer
if (keyedHmac2 == null)
{
K_i = keyedHmac.ComputeHash(bufferSegment.Array, bufferSegment.Offset, bufferSegment.Count);
}
else
{
keyedHmac2.TransformBlock(bufferSegment.Array, bufferSegment.Offset, bufferSegment.Count, null, 0);
keyedHmac2.TransformFinalBlock(bufferSegment.Array, 0, 0);
K_i = keyedHmac2.HashInner;
}
// copy the leftmost bits of K_i into the output buffer
int numBytesToCopy = derivedOutputCount > K_i.Length ? K_i.Length : derivedOutputCount;//Math.Min(derivedOutputCount, K_i.Length);
Utils.BlockCopy(K_i, 0, derivedOutput.Array, derivedOutputOffset, numBytesToCopy);
derivedOutputOffset += numBytesToCopy;
derivedOutputCount -= numBytesToCopy;
}// for
}// checked
if (keyedHmac2 == null && K_i != null) Array.Clear(K_i, 0, K_i.Length); /* clean up needed only when HMAC implementation is not HMAC2 */
}// DeriveKey()
}// DeriveKey()
internal static void DeriveKey(HMAC keyedHmac, ArraySegment<byte> bufferSegment, ArraySegment<byte> derivedOutput, uint counter = 1)
{
int derivedOutputCount = derivedOutput.Count, derivedOutputOffset = derivedOutput.Offset;
byte[] K_i = null;
checked
{
// Calculate each K_i value and copy the leftmost bits to the output buffer as appropriate.
for (var counterStruct = new Utils.IntStruct { UintValue = counter }; derivedOutputCount > 0; ++counterStruct.UintValue)
{
counterStruct.ToBEBytes(bufferSegment.Array, bufferSegment.Offset); // update the counter within the buffer
K_i = keyedHmac.ComputeHash(bufferSegment.Array, bufferSegment.Offset, bufferSegment.Count);
// copy the leftmost bits of K_i into the output buffer
int numBytesToCopy = Math.Min(derivedOutputCount, K_i.Length);
Utils.BlockCopy(K_i, 0, derivedOutput.Array, derivedOutputOffset, numBytesToCopy);
derivedOutputOffset += numBytesToCopy;
derivedOutputCount -= numBytesToCopy;
}// for
}// checked
if (K_i != null) Array.Clear(K_i, 0, K_i.Length);
}// DeriveKey()
