private static byte[] GenerateTmpGmacKey(GmacInfo gmacInfo, long index)
{
if (index != 0)
{
return(GenerateGmacKey(gmacInfo.KeyGmacBase, gmacInfo.Iv, index));
}
else
{
return(gmacInfo.KeyGmacCurrent);
}
}
/************************/
/**** private methods ***/
/************************/
private static byte[] GmacCrypto(GmacInfo gmacInfo, uint keyPos, byte[] buffer)
{
uint padding = keyPos % 16;
int size = (((int)padding + buffer.Length + 16 - 1) / 16) * 16;
byte[] keyStream = GenerateKeyStream(gmacInfo, keyPos - padding, size);
byte[] decryptedData = new byte[buffer.Length];
for (int i = 0; i < buffer.Length; i++)
{
decryptedData[i] = (byte)(buffer[i] ^ keyStream[padding + i]);
}
return(decryptedData);
}
public static byte[] GenerateKeyStream(GmacInfo gmacInfo, uint keyPos, int keyStreamSize)
{
var cipher = CipherUtilities.GetCipher("AES/ECB/NoPadding");
cipher.Init(true, new KeyParameter(gmacInfo.KeyBase));
int counterOffset = (int)keyPos / 16;
byte[] keyStream = new byte[keyStreamSize];
for (int i = 0; i < keyStreamSize; i += 16)
{
byte[] keyStreamPart = new byte[16];
SetGmacCounter(keyStreamPart, gmacInfo.Iv, counterOffset++);
Array.Copy(keyStreamPart, 0, keyStream, i, keyStreamPart.Length);
}
return(cipher.DoFinal(keyStream));
}
public static byte[] AddGmacToBuffer(GmacInfo gmacInfo, uint keyPos, byte[] buffer, int gmacPositionInBuffer)
{
//keyPos = (uint) System.Net.IPAddress.HostToNetworkOrder((int)keyPos);
byte[] iv = new byte[16];
SetGmacCounter(iv, gmacInfo.Iv, keyPos / 0x10);
byte[] gmacKey = gmacInfo.KeyGmacCurrent;
long keyIndex = (keyPos > 0 ? keyPos - 1 : 0) / GmacKeyRefreshKeyPosition;
if (keyIndex > gmacInfo.GmacCurrentIndex)
{
gmacKey = GenerateNewGmacKey(gmacInfo, keyIndex);
gmacInfo.KeyGmacCurrent = gmacKey;
gmacInfo.GmacCurrentIndex = keyIndex;
gmacKey = gmacInfo.KeyGmacCurrent;
}
else if (keyIndex < gmacInfo.GmacCurrentIndex)
{
gmacKey = GenerateTmpGmacKey(gmacInfo, keyIndex);
}
IMac mac = new GMac(new GcmBlockCipher(new AesEngine()), 32);
ICipherParameters key = new KeyParameter(gmacKey);
mac.Init(new ParametersWithIV(key, iv));
mac.BlockUpdate(buffer, 0, buffer.Length);
int macSize = mac.GetMacSize();
byte[] gmac = new byte[macSize];
mac.DoFinal(gmac, 0);
for (int i = 0; i < gmac.Length; i++)
{
buffer[gmacPositionInBuffer + i] = gmac[i];
}
return(gmac);
}
public static byte[] GenerateNewGmacKey(GmacInfo gmacInfo, long index)
{
return(GenerateGmacKey(gmacInfo.KeyGmacBase, gmacInfo.Iv, index));
}
public static byte[] DecryptGmacMessage(GmacInfo gmacInfo, uint keyPos, byte[] buffer)
{
return(GmacCrypto(gmacInfo, keyPos, buffer));
}