diff options
Diffstat (limited to 'doc/tor-spec.txt')
| -rw-r--r-- | doc/tor-spec.txt | 30 |
1 files changed, 18 insertions, 12 deletions
diff --git a/doc/tor-spec.txt b/doc/tor-spec.txt index 7c0297429..5536ef000 100644 --- a/doc/tor-spec.txt +++ b/doc/tor-spec.txt @@ -98,7 +98,7 @@ TODO: (very soon) proxies is a fixed-width "cell". Each cell contains the following fields: - CircID [2 bytes] + CircID [2 bytes] Command [1 byte] Payload (padded with 0 bytes) [509 bytes] [Total size: 512 bytes] @@ -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: - 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 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 two parts of DH data, once decrypted and concatenated, form - g^x as calculated by the client. + 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 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. |