internal static byte[] GetHmacKey64(byte[] pbKey, ulong uBlockIndex)
{
if(pbKey == null) throw new ArgumentNullException("pbKey");
Debug.Assert(pbKey.Length == 64);
// We are computing the HMAC using SHA-256, whose internal
// block size is 512 bits; thus create a key that is 512
// bits long (using SHA-512)
byte[] pbBlockKey;
using(SHA512Managed h = new SHA512Managed())
{
byte[] pbIndex = MemUtil.UInt64ToBytes(uBlockIndex);
h.TransformBlock(pbIndex, 0, pbIndex.Length, pbIndex, 0);
h.TransformBlock(pbKey, 0, pbKey.Length, pbKey, 0);
h.TransformFinalBlock(MemUtil.EmptyByteArray, 0, 0);
pbBlockKey = h.Hash;
}
#if DEBUG
byte[] pbZero = new byte[64];
Debug.Assert((pbBlockKey.Length == 64) && !MemUtil.ArraysEqual(
pbBlockKey, pbZero)); // Ensure we own pbBlockKey
#endif
return pbBlockKey;
}