/// <summary>
/// Decrypts a packet
/// </summary>
public static byte[] DecryptPacket(Packet p)
{
int packetID = p.ID;
byte[] encryptedPayload = p.Payload;
byte[] decryptedPayload;
if (packetID == 10100 || packetID == 20100)
{
// Both Session (10100) and SessionOk (20100) packets are not encrypted
// Thus.. just return the encrypted payload
return(encryptedPayload);
}
else if (packetID == 10101)
{
// The decrypted Login (10101) requires a nonce being calculated by the PK & the modded PK
_10101_PublicKey = encryptedPayload.Take(32).ToArray();
Blake2b.Init();
Blake2b.Update(_10101_PublicKey);
Blake2b.Update(Keys.ModdedPublicKey);
var tmpNonce = Blake2b.Finish();
// Decrypt the payload the custom NaCl
decryptedPayload = CustomNaCl.OpenPublicBox(encryptedPayload.Skip(32).ToArray(), tmpNonce, Keys.GeneratedPrivateKey, _10101_PublicKey);
_10101_SessionKey = decryptedPayload.Take(24).ToArray();
_10101_Nonce = decryptedPayload.Skip(24).Take(24).ToArray();
decryptedPayload = decryptedPayload.Skip(48).ToArray();
}
else if (packetID == 20103 || packetID == 20104)
{
// The decrypted LoginFailed / LoginOk (20103/20104) requires a nonce being calculated by the nonce from 10101, the custom PK & the original PK
Blake2b.Init();
Blake2b.Update(_10101_Nonce);
Blake2b.Update(CustomKeyPair.PublicKey);
Blake2b.Update(Keys.OriginalPublicKey);
var tmpNonce = Blake2b.Finish();
// Decrypt the payload with the custom NaCl
decryptedPayload = CustomNaCl.OpenPublicBox(encryptedPayload, tmpNonce, CustomKeyPair.SecretKey, Keys.OriginalPublicKey);
_20103_20104_Nonce = decryptedPayload.Take(24).ToArray();
_20103_20104_SharedKey = decryptedPayload.Skip(24).Take(32).ToArray();
decryptedPayload = decryptedPayload.Skip(56).ToArray();
}
else
{
if (p.Destination == DataDestination.DATA_FROM_CLIENT)
{
_10101_Nonce.Increment();
decryptedPayload = CustomNaCl.OpenSecretBox(new byte[16].Concat(encryptedPayload).ToArray(), _10101_Nonce, _20103_20104_SharedKey);
}
else
{
_20103_20104_Nonce.Increment();
decryptedPayload = CustomNaCl.OpenSecretBox(new byte[16].Concat(encryptedPayload).ToArray(), _20103_20104_Nonce, _20103_20104_SharedKey);
}
}
return(decryptedPayload);
}
