new security consideration: PROBES might expose common creditor ancestors

[michielbdejong]

if DFS backtracks, and a forward or cross edge exists, some nodes may find out if some of their in-neighbors (i.e., creditors) have a common ancestor.

[michielbdejong]

one solution would be to always only try one sibling out-neighbor, which might not be such a bad idea, given that if ddcd did its work well, backtracks should normally be quite rare.

[michielbdejong]

Discovering common creditor ancestors is actually a feature if you want to balance those creditors against each other. Still worth mentioning this security consideration in the whitepaper or in the FAQ, though.

[michielbdejong]

this is already discussed in the Traffic Analysis section of the whitepaper.