Keeping data secret, or not

[mtbc]

With secure communication online (TLS, etc.) it is interesting to see how standards develop: older ways are later judged insecure and the community slowly moves onto newer ones. I have wondered if the security services, and others, record some of the more interesting traffic that they can't decrypt yet in the hope that new developments might someday reveal the content of those once-private communications. People move on to different algorithms for actual reasons. Even if past the statute of limitations for prosecution, such records may still yield useful intelligence.

Now, given my job, I think about cryptocurrency more. There are some currencies, popular for payments for illegal services, that are designed to obscure the details of transfers. Even with normal cryptocurrencies, whose transfers are easily observed, there are tumblers which are busy accounts that take in many and various payments, and make payouts differently and rather later, so as to obscure the flows: they make it difficult to match the incoming funds against the outgoing.

I had already been wondering if statistical analysis of activity around tumblers may at least circumstantially reveal repeated flows for habitual users. Now I also wonder if some of the privacy-enhanced cryptocurrencies may be found to be less private than currently assumed, which would be interesting given that the blockchain records all the data publicly and long-term.

In short: as new discoveries uncover historical information, perhaps some people have bad surprises waiting for them.