Add IP:Port:KeyDigest format to rend-spec.txt

         PK    Bob's public key                      [KL octets]

         TS    A timestamp                           [4 octets]

         NI    Number of introduction points         [2 octets]

         Ipt   A list of NUL-terminated OR nicknames [variable]

         Ipt   A list of NUL-terminated ORs         [variable]

         SIG   Signature of above fields             [variable]

   KL is the length of PK, in octets.  (Currently, KL must be 128.)

   TS is the number of seconds elapsed since Jan 1, 1970.

   The members of Ipt may either be OR nicknames, or IP:Port:ID-key-hash

   triples.  Servers must accept both forms.  Before 0.0.7 is obsoleted,

   servers should only generate the first form.

   [It's ok for Bob to advertise 0 introduction points. He might want

    to do that if he previously advertised some introduction points,

    and now he doesn't have any. -RD]

   [Shouldn't the nicknames be hostname:port's instead?  That way, Alice's

   directory servers don't need to know Bob's chosen introduction points.

   Not important now, but essential if we ever have a non-total-knowledge

   design. -NM]

1.3. Bob's OP establishes his introduction points.

   The OP establishes a new introduction circuit to each introduction

   currently associated with PK.  On success, the OR sends Bob a

   RELAY_INTRO_ESTABLISHED cell with an empty payload.

1.4. Bob's OP advertises his server descriptor

1.4. Bob's OP advertises his service descriptor

   Bob's OP opens a stream to each directory server's directory port via Tor.

   (He may re-use old circuits for this.)

       Encrypted to Bob's PK:

          RP     Rendezvous point's nickname  [20 octets]

          RC     Rendezvous cookie            [20 octets]

          g^x    Diffie-Hellman data, part 1 [128 octetes]

          g^x    Diffie-Hellman data, part 1 [128 octets]

       OR

          VER    Version byte: set to 4.        [1 octet]

          RP:IP  IP of rendezvous point        [4 octets]

          RP:P   Port of rendezvous point      [2 octets]

          RP:ID  ID key hash of rendezvous pt [20 octets]

          RC     Rendezvous cookie            [20 octets]

          g^x    Diffie-Hellman data, part 1 [128 octets]

   PK_ID is the hash of Bob's public key.  RP is NUL-padded.

   Implementations must accept both variants, but should only generate the

   first so long as Tor 0.0.7.

   The hybrid encryption to Bob's PK works just like the hybrid

   encryption in CREATE cells (see main spec). Thus the payload of the

   RELAY_INTRODUCE1 cell on the wire will contain 20+42+16+20+20+128=246