commit e3fab7bfbff6c6d82d9303dc90c4147421ba33ba Author: Damian Johnson atagar@torproject.org Date: Thu May 24 12:16:50 2018 -0700

Incorrect circuit digest for higher protocol versions

I only got stem.client working for link protocol 3 when cobbling it together. We attempt to conform with the spec for higher protocol versions but it's mostly untested.

While looking into #26060 I realized that we're using the wrong length for cell headers when the link protocol is higher than three. Link v4 and greater use a long for circuit identifiers rather than a short...

circ_id (4 bytes) + command (1 byte) = 5 bytes --- stem/client/__init__.py | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/stem/client/__init__.py b/stem/client/__init__.py index 6e25f748..281888e7 100644 --- a/stem/client/__init__.py +++ b/stem/client/__init__.py @@ -235,20 +235,26 @@ class Circuit(object): orig_digest = self.forward_digest.copy() orig_key = copy.copy(self.forward_key)

+ # Digests and such are computed using the RELAY cell payload. This + # doesn't include the initial circuit id and cell type fields. + # Circuit ids vary in length depending on the protocol version. + + header_size = 5 if self.relay.link_protocol > 3 else 3 + try: cell = stem.client.cell.RelayCell(self.id, command, data, 0, stream_id) - payload_without_digest = cell.pack(self.relay.link_protocol)[3:] + payload_without_digest = cell.pack(self.relay.link_protocol)[header_size:] self.forward_digest.update(payload_without_digest)

cell = stem.client.cell.RelayCell(self.id, command, data, self.forward_digest, stream_id) - header, payload = split(cell.pack(self.relay.link_protocol), 3) + header, payload = split(cell.pack(self.relay.link_protocol), header_size) encrypted_payload = header + self.forward_key.update(payload)

reply = [] self.relay._orport.send(encrypted_payload)

for cell in stem.client.cell.Cell.unpack(self.relay._orport.recv(), self.relay.link_protocol): - decrypted = self.backward_key.update(cell.pack(self.relay.link_protocol)[3:]) + decrypted = self.backward_key.update(cell.pack(self.relay.link_protocol)[header_size:]) reply.append(stem.client.cell.RelayCell._unpack(decrypted, self.id, self.relay.link_protocol))

return reply