private byte[] ComputeHeaderHmac(byte[] pbHeader, byte[] pbKey)
{
byte[] pbHeaderHmac;
byte[] pbBlockKey = HmacBlockStream.GetHmacKey64(
pbKey, ulong.MaxValue);
using(HMACSHA256 h = new HMACSHA256(pbBlockKey))
{
pbHeaderHmac = h.ComputeHash(pbHeader);
}
MemUtil.ZeroByteArray(pbBlockKey);
return pbHeaderHmac;
}
/// <summary>
/// Create a cryptographic key of length <paramref name="cbOut" />
/// (in bytes) from <paramref name="pbIn" />.
/// </summary>
public static byte[] ResizeKey(byte[] pbIn, int iInOffset,
int cbIn, int cbOut)
{
if (pbIn == null)
{
throw new ArgumentNullException("pbIn");
}
if (cbOut < 0)
{
throw new ArgumentOutOfRangeException("cbOut");
}
if (cbOut == 0)
{
return(MemUtil.EmptyByteArray);
}
byte[] pbHash;
if (cbOut <= 32)
{
pbHash = HashSha256(pbIn, iInOffset, cbIn);
}
else
{
using (SHA512Managed h = new SHA512Managed())
{
pbHash = h.ComputeHash(pbIn, iInOffset, cbIn);
}
}
if (cbOut == pbHash.Length)
{
return(pbHash);
}
byte[] pbRet = new byte[cbOut];
if (cbOut < pbHash.Length)
{
Array.Copy(pbHash, pbRet, cbOut);
}
else
{
int iPos = 0;
ulong r = 0;
while (iPos < cbOut)
{
Debug.Assert(pbHash.Length == 64);
using (HMACSHA256 h = new HMACSHA256(pbHash))
{
byte[] pbR = MemUtil.UInt64ToBytes(r);
byte[] pbPart = h.ComputeHash(pbR);
int cbCopy = Math.Min(cbOut - iPos, pbPart.Length);
Debug.Assert(cbCopy > 0);
Array.Copy(pbPart, 0, pbRet, iPos, cbCopy);
iPos += cbCopy;
++r;
MemUtil.ZeroByteArray(pbPart);
}
}
Debug.Assert(iPos == cbOut);
}
#if DEBUG
byte[] pbZero = new byte[pbHash.Length];
Debug.Assert(!MemUtil.ArraysEqual(pbHash, pbZero));
#endif
MemUtil.ZeroByteArray(pbHash);
return(pbRet);
}
