I am teaching Anonymous Networks in a Cybersecurity class. I am understanding (what I think) is a good deal about the process TORproject uses for its network by using this as a guide.


My model of the process is that as an 'onion' travels down the circuit, the number of scramblings of the message is reduced by 1 each time. The scrambled message needs some unscrambled part to know where to send next. The information at the entry node would be larger in size than the exit node because the message at the exit node has fewer instructions about how to get to its destination.

My question is:

Can the distance along the circuit be determined by the size of the encrypted message? OR Can the key be deduced by having consistent information (perhaps metadata headers??) about the destination?

1 Answer 1


You're not wrong (except for The Key being deduced part) but the approach is meaningless.

You are implicitly assuming information you don't have to solve a problem that doesn't exist. I'll try to explain.

You are assuming that you can track a given message through all of its relays in order to compute message size reduction at each relay. First of all data is in fixed sized packets but there is no padding so in principle you could do this by counting packets but it requires an overarching knowledge of all of the network traversal packets. If you had this level of insight, you wouldn't need to do the analysis in the first place.

The default Tor circuit is 3 nodes: Entry Node,Relay Node, Exit Node. All of the Tor nodes and types are public information already. The "distance" of the circuit is always (mostly) 3. The distance along the circuit is a function of the node in the circuit. If you're already somehow tracing the packet, you already know the hop count without trying to compute packet reduction inference.

In short, you need comprehensive knowledge to compute something you would already know.

I don't know what you mean by "The Key", but it doesn't really matter as your system requires apriori knowledge of the entire circuit, negating all of the individual hop keys anyway.

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