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clarify the hybrid encryption in our spec

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svn:r1736
This commit is contained in:
Roger Dingledine 2004-04-28 20:01:54 +00:00
parent 25d5425fdb
commit fd0d48e484
3 changed files with 25 additions and 33 deletions
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18
doc/TODO
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@ -11,21 +11,6 @@ ARMA - arma claims
D Deferred
X Abandoned
Flag-day changes: (things which are backward incompatible)
o remove link key from directories, from connection_t.
(just get it from the tls cert)
o Generate link keys on startup; don't store them to disk.
o make onion keys include oaep padding, so you can tell
if you decrypted it correctly
o Rotate onion keys as needed
D Rotate TLS connections [arma]
o Set expiration times on X509 certs [nickm]
o add bandwidthrate and bandwidthburst to server descriptor [nickm]
o directories need to say who signed them. [nickm]
- remove assumption that 0.0.5 doesn't do rendezvous?
D what other pieces of the descriptors need to change?
maybe add a section for who's connected to a given router?
add a flexible section for reputation info?
For September:
- Windows port
@ -69,6 +54,9 @@ For September:
- allow non-clique topology
Other details and small things:
- hidserv offerers shouldn't need to define a SocksPort
- when the client fails to pick an intro point for a hidserv,
it should refetch the hidserv desc.
. should maybe make clients exit(1) when bad things happen?
e.g. clock skew.
- should retry exitpolicy end streams even if the end cell didn't

10
doc/rend-spec.txt
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@ -255,12 +255,10 @@ Tor Rendezvous Spec
PK_ID is the hash of Bob's public key. RP is NUL-padded.
The data is encrypted to Bob's PK as follows: Suppose Bob's PK is L octets
long. If the data to be encrypted is shorter than L-42, then it is
encrypted directly (with OAEP padding). If the data is at least as long
as L-42, then a randomly generated 16-byte symmetric key is prepended to
the data, after which the first L-16-42 bytes of the data are encrypted with
Bob's PK; and the rest of the data is encrypted with the symmetric key.
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
bytes.
1.9. Introduction: From the Introduction Point to Bob's OP

28
doc/tor-spec.txt
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@ -146,23 +146,29 @@ TODO: (very soon)
which instructs the last node in the circuit to send a CREATE cell
to extend the circuit.
The payload for a CREATE cell is an 'onion skin', consisting of:
RSA-encrypted data [128 bytes]
Symmetrically-encrypted data [16 bytes]
The payload for a CREATE cell is an 'onion skin', which consists
of the first step of the DH handshake data (also known as g^x).
The RSA-encrypted portion contains:
The data is encrypted to Bob's PK as follows: Suppose Bob's PK is
L octets long. If the data to be encrypted is shorter than L-42,
then it is encrypted directly (with OAEP padding). If the data is at
least as long as L-42, then a randomly generated 16-byte symmetric
key is prepended to the data, after which the first L-16-42 bytes
of the data are encrypted with Bob's PK; and the rest of the data is
encrypted with the symmetric key.
So in this case, the onion skin on the wire looks like:
RSA-encrypted:
OAEP padding [42 bytes]
Symmetric key [16 bytes]
First part of DH data (g^x) [112 bytes]
The symmetrically encrypted portion contains:
Second part of DH data (g^x) [16 bytes]
The two parts of DH data, once decrypted and concatenated, form
g^x as calculated by the client.
First part of g^x [70 bytes]
Symmetrically encrypted:
Second part of g^x [58 bytes]
The relay payload for an EXTEND relay cell consists of:
Address [4 bytes]
Port [2 bytes]
Onion skin [144 bytes]
Onion skin [186 bytes]
The port and address field denote the IPV4 address and port of the
next onion router in the circuit.