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arma@last-request:~/old/torgit/torspec/proposals$ telnet localhost 9051
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
authenticate
250 OK
quit
250 closing connection
Connection closed by foreign host.
arma@last-request:~/old/torgit/torspec/proposals$ nc localhost 9051
authenticate
551 Invalid quoted string.  You need to put the password in double quotes.
arma@last-request:~/old/torgit/torspec/proposals$ nc localhost 9051
authenticate ""
250 OK
quit
250 closing connection

Setting up logging on Tor's side in handle_control_authenticate():

 log_notice(LD_CONTROL, "'%s'", body);

in the first case I get

Apr 11 16:39:13.633 [notice] '
'

and in the second case I get

Apr 11 16:39:23.258 [notice] ''

It looks like that function is checking

  } else if (TOR_ISSPACE(body[0])) {
    password = tor_strdup("");
    password_len = 0;
  }

So Tor demands that you have some sort of whitespace before your newline. That runs counter to our spec:

  Wherever CRLF is specified to be accepted from the controller, Tor MAY also
  accept LF.  Tor, however, MUST NOT generate LF instead of CRLF.
  Controllers SHOULD always send CRLF.