Module authchallenge

stem_rs::response

Module authchallenge 

Source
Expand description

AUTHCHALLENGE response parsing.

This module parses responses from the AUTHCHALLENGE command, which is used during SAFECOOKIE authentication. SAFECOOKIE is the most secure authentication method for local Tor connections, using HMAC-SHA256 challenge-response.

§Protocol Overview

SAFECOOKIE authentication works as follows:

  1. Client sends AUTHCHALLENGE SAFECOOKIE <client_nonce>
  2. Server responds with SERVERHASH and SERVERNONCE
  3. Client computes HMAC-SHA256(cookie || client_nonce || server_nonce)
  4. Client sends AUTHENTICATE <computed_hash>

§Response Format

250 AUTHCHALLENGE SERVERHASH=<64_hex_chars> SERVERNONCE=<64_hex_chars>

Both values are 32-byte (256-bit) values encoded as 64 hexadecimal characters.

§Example

use stem_rs::response::{ControlMessage, AuthChallengeResponse};

let response_text = "250 AUTHCHALLENGE \
    SERVERHASH=680A73C9836C4F557314EA1C4EDE54C285DB9DC89C83627401AEF9D7D27A95D5 \
    SERVERNONCE=F8EA4B1F2C8B40EF1AF68860171605B910E3BBCABADF6FC3DB1FA064F4690E85\r\n";
let msg = ControlMessage::from_str(response_text, None, false).unwrap();
let response = AuthChallengeResponse::from_message(&msg).unwrap();

assert_eq!(response.server_hash.len(), 32);
assert_eq!(response.server_nonce.len(), 32);

§Security Considerations

  • The server hash proves the server knows the cookie file contents
  • The server nonce prevents replay attacks
  • Both values should be used exactly once per authentication attempt
  • Failed authentication should trigger a new challenge with fresh nonces

§See Also

Structs§

AuthChallengeResponse
Parsed response from the AUTHCHALLENGE command.