Possible packet types: EXTENDED or RELAY. Recipient knows it has with each hop in the circuit, starting from the endpoint The packet is decrypted concurrently with AES and the shared secrets that the Circuit identifier + sender combination known, first node in circuit.Knows it has with the circuit identifier. The packet is decrypted with AES and the shared secret that the recipient Circuit identifier + sender combination known, last node in circuit.Unencrypted packet is unreadable or not a CREATE packet. The packet is decrypted with the private key of the recipient. Circuit identifier + sender combination unknown.The circuit identifier and position of the node in the circuit: There are five different ways to decrypt an incoming packet which depend on Upstream and downstream traffic use different keys. To prevent IV reuse, IVs are constructed from a counter and a fixed part determined during key agreement. For each message, its contents are encrypted as a separate GCM stream. The packet header is unencrypted and consists only of the circuit identifier. Once this process has completed, a shared secret is agreed upon through the use of Curve25519 Elliptic Curve Diffie–Hellman.Īfter having established a shared secret, all subsequent packets will be partially encrypted using AES-GCM-128. Next, both nodes exchange CREATE/CREATED messages which are used to inform one another about their respective public keys. The detailed byte-accurate specification of our enhanced Tor-subset is as follows:Įvery time a circuit is extended with an additional node, the creator of the circuit and the node with which the circuit is to be extended randomly generate a new keypair. We use a simple Socks5 interface to talk to the circuits. Show below is the onion encryption and decryption. PING Requests a PONG for keep-alive purposes, also used for circuit breakdown detection.If a packet cannot be routed it will be sent over a direct line, the sending node acts as EXIT node. DATA Transferring data between nodes is done using the DATA packet.EXTENDED If the circuit has been extended the EXTENDED message propagates back to the origin.EXTEND When a node wants to extend its circuit it sends an EXTEND message along the circuit.
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