more spec clarifications from talking to lexi

   Unless otherwise specified, all symmetric ciphers are AES in counter

   mode, with an IV of all 0 bytes.  Asymmetric ciphers are either RSA

   with 1024-bit keys and exponents of 65537, or DH where the generator

   is 2 and the modulus is the safe prime from rfc2409, section 6.2,

   whose hex representation is:

   is 2 and the modulus is the 1024-bit safe prime from rfc2409,

   section 6.2, whose hex representation is:

     "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E08"

     "8A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B"

   (The digest does not include any bytes from relay cells that do

   not start or end at this hop of the circuit. That is, it does not

   include forwarded data.)

   include forwarded data. Therefore if 'recognized' is zero but the

   digest does not match, the running digest at that node should

   not be updated, and the cell should be forwarded on.)

   All RELAY cells pertaining to the same tunneled stream have the

   same stream ID.  StreamIDs are chosen arbitrarily by the OP.  RELAY