commit a6e012508e5b0d676cdf204fcbd7942e3cc21419 Author: David Goulet <dgoulet@torproject.org> Date: Tue Feb 19 15:02:11 2019 -0500 prop289: Add random bytes to the unused portion of the cell Signed-off-by: David Goulet <dgoulet@torproject.org> --- src/core/or/relay.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/src/core/or/relay.c b/src/core/or/relay.c index 47275a811..63c406d8a 100644 --- a/src/core/or/relay.c +++ b/src/core/or/relay.c @@ -572,6 +572,14 @@ relay_send_command_from_edge_,(streamid_t stream_id, circuit_t *circ, if (payload_len) memcpy(cell.payload+RELAY_HEADER_SIZE, payload, payload_len); + /* Add random bytes to the unused portion of the payload, to foil attacks + * where the other side can predict all of the bytes in the payload and thus + * compute authenticated sendme cells without seeing the traffic. See + * proposal 289. */ + crypto_fast_rng_getbytes(get_thread_fast_rng(), + cell.payload + RELAY_HEADER_SIZE + payload_len, + RELAY_PAYLOAD_SIZE - payload_len); + log_debug(LD_OR,"delivering %d cell %s.", relay_command, cell_direction == CELL_DIRECTION_OUT ? "forward" : "backward");