Current state

In case the validation of a ticket or packet fails, no acknowledgement is sent. Although this saves bandwidth, it reveals data to a potential observer. More specifically, the passive observer can figure out that a mixnet packet has not been relayed - which massively decreases the privacy.

How to fix it

Acknowledge all packets. In case, a ticket gets rejected, or the packet is invalid, send a random acknowledgement. The probability is negligible that this randomly chosen value matches any of the sender's requested hashes, so the sender is able to understand that the packet and / or ticket got rejected - but a passive adversary will not.

• send a random acknowledgement in case packet and / or ticket got dropped