/// <summary>
/// Converts a signature to a signed packet. Take note that during this process,
/// the signature will be verified based on the desired algorithm.
/// </summary>
/// <param name="signature">Signature to convert.</param>
/// <param name="remoteIdentity">Identity of the sender of this signed packet. May not always be the signer.</param>
/// <param name="signatureAlgorithm">Algorithm to verify the signature with.</param>
/// <param name="packetFactory">Packet factory to create the packet from.</param>
/// <returns>Signed packet.</returns>
public static PacketSigned FromSignature(Signature signature, Identity remoteIdentity, SignatureAlgorithm signatureAlgorithm, PacketFactory packetFactory)
{
if (signatureAlgorithm == null)
{
throw new SecurityException("Null signature algorithm provided.");
}
MemoryStream signaturePacketBuffer = new MemoryStream(signature.Data);
BinaryReader stream = new BinaryReader(signaturePacketBuffer);
//Read the cryptographic salt from the packet, skipping it to advance forward.
stream.ReadInt32();
//Read the time the signature was created.
DateTime signatureDate = new DateTime(stream.ReadInt64(), DateTimeKind.Utc);
//Read the ID from the packet.
byte packetId = stream.ReadByte();
//Create the packet from the factory using the ID read.
ReliableIM.Network.Protocol.Packet packet = packetFactory.CreateFromId(packetId);
if (!(packet is PacketSigned))
{
throw new SecurityException("Packet type not acceptable.");
}
//Set the date time instance.
((PacketSigned)packet).dateTime = signatureDate;
//Read the packet contents into the factory's packet.
packet.Read(stream);
//Verify the packet's signature against the given algorithm.
if (!((PacketSigned)packet).VerifySignature(signatureAlgorithm, signature, remoteIdentity.Equals(signatureAlgorithm.Identity)))
{
throw new SecurityException("Signature verification failed.");
}
//Warning: At this point the signature has been verified, and authenticity
//of the packet's origin (regardless of route) is no longer questioned.
return((PacketSigned)packet);
}