/// <summary>
/// Encrypts a packet targeted to a single person
/// </summary>
/// <param name="packet">The packet to encrypt</param>
/// <param name="targetPublicKey">Target's identity public key</param>
/// <returns>Encrypted packet</returns>
public static DEncodeValue EncryptTargetedPacket(DEncodeValue packet, byte[] targetPublicKey)
{
var targetCryptCsp = new RSACryptoServiceProvider();
targetCryptCsp.ImportCspBlob(targetPublicKey);
var packetStream = new MemoryStream();
var writer = new DEncodeWriter(packetStream);
writer.Write(packet);
var packetBytes = packetStream.ToArray();
// create a unique packet key
var csp = CreatePacketCryptingAlgoInstance();
var key = new byte[32];
var iv = new byte[32];
RngCsp.GetBytes(key);
RngCsp.GetBytes(iv);
csp.Key = key;
csp.IV = iv;
// encrypt the packet
var cryptedPacketBytes = csp.CreateEncryptor().TransformFinalBlock(packetBytes, 0, packetBytes.Length);
// now encrypt the packet key with the target's public key
var encryptedKey = targetCryptCsp.Encrypt(key, true);
var packetDict = new Dictionary<string, DEncodeValue>();
packetDict.Add("ty", new DEncodeString("targeted")); // type (encrypted, targeted packet)
packetDict.Add("ke", new DEncodeArray(encryptedKey)); // packet encryption key (encrypted with target's public key)
packetDict.Add("iv", new DEncodeArray(iv)); // IV for the packet encryption
packetDict.Add("pa", new DEncodeArray(cryptedPacketBytes)); // wrapped payload packet
return new DEncodeDictionary(packetDict);
}
/// <summary>
/// Encrypts a packet without any specific target (= targeting the whole chat session) using a master key
/// </summary>
/// <param name="packet">The packet to encrypt</param>
/// <param name="masterKey">The master key to use for encryption</param>
/// <returns>Encrypted packet</returns>
public static DEncodeValue EncryptNonTargetedPacket(DEncodeValue packet, byte[] masterKey)
{
var packetStream = new MemoryStream();
var writer = new DEncodeWriter(packetStream);
writer.Write(packet);
var packetBytes = packetStream.ToArray();
// create a unique packet key
var csp = CreatePacketCryptingAlgoInstance();
var iv = new byte[32];
RngCsp.GetBytes(iv);
csp.Key = masterKey;
csp.IV = iv;
// encrypt the packet
var cryptedPacketBytes = csp.CreateEncryptor().TransformFinalBlock(packetBytes, 0, packetBytes.Length);
var packetDict = new Dictionary<string, DEncodeValue>();
packetDict.Add("ty", new DEncodeString("nontargeted")); // type (encrypted, targeted packet)
packetDict.Add("iv", new DEncodeArray(iv)); // IV for the packet encryption
packetDict.Add("pa", new DEncodeArray(cryptedPacketBytes)); // wrapped payload packet
return new DEncodeDictionary(packetDict);
}
/// <summary>
/// Sends a Crype packet to the chatroom
/// </summary>
/// <param name="packet">Crype packet body</param>
public void SendPacket(DEncodeValue packet)
{
var packetWriterStream = new MemoryStream();
var packetWriter = new DEncodeWriter(packetWriterStream);
packetWriter.Write(packet);
var messageToSend = Convert.ToBase64String(packetWriterStream.ToArray());
_chatImpl.SendMessage(messageToSend);
}
/// <summary>
/// Parses a packet decrypting it if necessary. Returns the unwrapped plain packet and information about the options of the packet
/// </summary>
/// <param name="packet">The packet</param>
/// <param name="targetedDecryptorCsp">RSA instance to decrypt targeted packets</param>
/// <param name="untargetedMasterKey">Master key to decrypt untargeted packets on chat</param>
/// <returns>The unwrapped packet and information about it</returns>
public static PacketInfo UnwrapPacket(DEncodeValue packet, RSACryptoServiceProvider targetedDecryptorCsp,
byte[] untargetedMasterKey)
{
var packetDict = (DEncodeDictionary) packet;
var type = ((DEncodeString) packetDict.Items["ty"]).Value;
if (type == "plain")
{
return new PacketInfo(packet, false, null, false, false);
}
if (type == "sigwrap")
{
var signedByKey = ((DEncodeArray) packetDict.Items["sb"]).Value;
var signature = ((DEncodeArray) packetDict.Items["si"]).Value;
var wrappedPacket = packetDict.Items["pa"];
var packetStream = new MemoryStream();
var writer = new DEncodeWriter(packetStream);
writer.Write(wrappedPacket);
var wrappedPacketBytes = packetStream.ToArray();
var validatorCsp = new RSACryptoServiceProvider();
validatorCsp.ImportCspBlob(signedByKey);
if (!validatorCsp.VerifyHash(ComputeSha1Hash(wrappedPacketBytes), Sha1Csp.ToString(), signature))
{
throw new CryptographicException("Invalid signature");
}
var wrappedPacketInfo = UnwrapPacket(wrappedPacket, targetedDecryptorCsp, untargetedMasterKey);
wrappedPacketInfo.IsSigned = true;
wrappedPacketInfo.SignedByKey = signedByKey;
return wrappedPacketInfo;
}
if (type == "targeted")
{
var encryptedPacketKey = ((DEncodeArray) packetDict.Items["ke"]).Value;
var iv = ((DEncodeArray) packetDict.Items["iv"]).Value;
var encryptedPacketBytes = ((DEncodeArray) packetDict.Items["pa"]).Value;
// decrypt the packet key
var packetKey = targetedDecryptorCsp.Decrypt(encryptedPacketKey, true);
// decrypt the packet
var decryptorCsp = CreatePacketCryptingAlgoInstance();
decryptorCsp.Key = packetKey;
decryptorCsp.IV = iv;
var decryptedPacketBytes = decryptorCsp.CreateDecryptor()
.TransformFinalBlock(encryptedPacketBytes, 0,
encryptedPacketBytes.Length);
// parse the wrapped packet
var reader = new DEncodeReader(new MemoryStream(decryptedPacketBytes));
var wrappedPacket = reader.Read();
var wrappedPacketInfo = UnwrapPacket(wrappedPacket, targetedDecryptorCsp, untargetedMasterKey);
wrappedPacketInfo.IsTargeted = true;
return wrappedPacketInfo;
}
if (type == "nontargeted")
{
var iv = ((DEncodeArray)packetDict.Items["iv"]).Value;
var encryptedPacketBytes = ((DEncodeArray)packetDict.Items["pa"]).Value;
// decrypt the packet
var decryptorCsp = CreatePacketCryptingAlgoInstance();
decryptorCsp.Key = untargetedMasterKey;
decryptorCsp.IV = iv;
var decryptedPacketBytes = decryptorCsp.CreateDecryptor()
.TransformFinalBlock(encryptedPacketBytes, 0,
encryptedPacketBytes.Length);
// parse the wrapped packet
var reader = new DEncodeReader(new MemoryStream(decryptedPacketBytes));
var wrappedPacket = reader.Read();
var wrappedPacketInfo = UnwrapPacket(wrappedPacket, targetedDecryptorCsp, untargetedMasterKey);
wrappedPacketInfo.IsUntargeted = true;
return wrappedPacketInfo;
}
throw new Exception("Invalid packet type code");
}
/// <summary>
/// Signs a packet with RSA
/// </summary>
/// <param name="packet">The packet to sign</param>
/// <param name="signingCsp">RSA instance with private key used to sign the packet</param>
/// <returns>Signed packet</returns>
public static DEncodeValue SignPacket(DEncodeValue packet, RSACryptoServiceProvider signingCsp)
{
var packetStream = new MemoryStream();
var writer = new DEncodeWriter(packetStream);
writer.Write(packet);
// sign the wrapped packet
var packetBytes = packetStream.ToArray();
var packetHash = ComputeSha1Hash(packetBytes);
var signature = signingCsp.SignHash(packetHash, Sha1Oid);
// create a wrapper packet with the original packet inside it
var packetDict = new Dictionary<string, DEncodeValue>();
packetDict.Add("ty", new DEncodeString("sigwrap")); // type (signature wrapper)
packetDict.Add("sb", new DEncodeArray(signingCsp.ExportCspBlob(false))); // public key blob of the signer
packetDict.Add("si", new DEncodeArray(signature)); // signature of payload
packetDict.Add("pa", packet); // wrapped payload packet
return new DEncodeDictionary(packetDict);
}
