commit 0713f2b4cbdeed5052f5b11f42912eff73a49d2a Author: David Goulet dgoulet@torproject.org Date: Mon Jan 7 16:42:27 2019 -0500
prop289: Spec out the new SENDME cell payload
Signed-off-by: David Goulet dgoulet@torproject.org --- proposals/289-authenticated-sendmes.txt | 42 ++++++++++++++++++++++++--------- 1 file changed, 31 insertions(+), 11 deletions(-)
diff --git a/proposals/289-authenticated-sendmes.txt b/proposals/289-authenticated-sendmes.txt index e7605dc..3ec7fd6 100644 --- a/proposals/289-authenticated-sendmes.txt +++ b/proposals/289-authenticated-sendmes.txt @@ -223,17 +223,37 @@ Status: Open (100) has arrived. So the client should use the digest from the cell that triggers the sendme.
- How shall we version the sendme payload so we can change the format of - it later? Right now sendme payloads are empty. Here's a simple design: - we use five bytes in the payload, where the first byte indicates the - sendme payload version (0 in the original design, and 1 once we've - implemented this proposal), and the rest of the payload is formatted - based on the payload version number: in this case, it's simply the - four bytes of digest. - - Is there a better way to version the payload, e.g. a way that is - already standard in other parts of the design, so we aren't adding - a new paint color to keep track of on the bike shed? + In order to achieve this, we need to version the SENDME cell so we can + differentiate the original protocol versus the new authenticated cell. + Right now, the SENDME payload is empty which translate to a version value + of 0 with this proposed change. The version to achieve authenticated + SENDMEs of this proposal would be 1. + + The SENDME cell payload would contain the following: + + VERSION [1 byte] + DATA_LEN [2 bytes] + DATA [DATA_LEN bytes] + + The VERSION tells us what is expected in the DATA section of length + DATA_LEN. The recognized values are: + + 0x00: The rest of the payload should be ignored. + + 0x01: Authenticated SENDME. The DATA section should contain: + + DIGEST [4 bytes] + + If the DATA_LEN value is less then 4 bytes, the cell should be dropped + and the circuit closed. If the value is more than 4 bytes, then the + first 4 bytes should be read to get the correct value. + + The DIGEST is the digest value from the cell that triggered this SENDME + as mentionned above. This value is matched on the other side from the + previous cell. + + If a VERSION is unrecognized, the SENDME cell should be treated as version + 0 meaning the payload is ignored.
3.2. Verifying the sendme payload