3

Just wondering, which protocol, TAP or NTor is less computationally intensive for a relay to process and why ?

Thanks Rich

5

ntor offers reduced computational complexity for circuit setup compared to TAP. Tor circuits are setup one hop at a time with each link using TLS. Diffie-Hellman (DH) is the algorithm used for computing keys to be exchanged and is responsible for what we conceptually know as forward-secrecy.

Notable differences between TAP and ntor

Tor Authentication Protocol (TAP), the original/legacy handshake, will be used where ntor isn't supported.

  • Generating a DH key is computationally expensive
  • Need to generate DH public/private values, and perform exchange at each node, as the circuit is extended
  • DH Keys are encrypted/decrypted with RSA at each node using onion-key
  • An analysis of TAP can be found here

ntor is the handshake added in 0.2.4.8-alpha. It will be used where consensus method is at least 16 and an ntor public key is available.

-- leeroy

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