As a part of my thesis, I am about to evaluate different approaches to establish the trust in trusted-timestamping performed by a TSA (see RFC3161 - Trusted Timestamp Protocol). A trustworthy timestamping scheme must provide the following property, taken from the basic paper on this topic (found here):

It is impossible to timestamp a document with a time and date different from the actual one.

What I want to figure out during my work is, under which assumptions it is plausible that the given statement holds.

I want to use these assumptions in the next step, to evaluate in how far an approach is suited to establish trust.

My question now is: Do you know a framework or approach I can use, to deduce the required assumptions from the given statement (or a more precise version of it)?

Here one example to clear things up a little more: One approach going to be evaluated is posting timestamps in a blockchain. What I am looking for is a systematic approach to estimate whether this way of making timestamps immutable is trustworthy or not.

  • You can use 3rd party service like CAs. Or line with 2FA (tokens). So for example, you generate signature of the document, and then sign it with 3rd party service. This can then be verified by the built-in certs. – Aria Sep 23 '16 at 12:51
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    Unless you have a trusted timekeeper, that property is impossible to achieve. The problem is, there is no such thing as objectively trustworthy time, this is guaranteed by relativity. The best you can do in practical engineering is to get close enough, with distributed blockchain, you can assert the sequences of events. With enough independent parties duplicating and verifying the blockchain, you can limit the range of time for forged time to a very narrow time slice. – Lie Ryan Sep 23 '16 at 15:46
  • @Aria Thats a good idea though It's another example for services I might evaluate by the approach I am looking for. – Maximilian Beckmann Sep 26 '16 at 8:26
  • @LieRyan Your argumentation is exactly what I want to accomplish within my thesis. My goal is to provide a list of assumptions you need all participiant to be ok with. To trust for example a conventional TSA (a trusted timekeeper) you have to assume, that every participant is trusting the timekeeper. Regarding your other example: to trust the blockchain you need to assume its immutability. What I am looking for is a way to rather narrowing down these assumptions instead of simply postulating them. I am looking for sth. like: cs.cmu.edu/~dg/papers/sp2010-preprint.pdf – Maximilian Beckmann Sep 26 '16 at 8:35
  • @MaximilianBeckmann: blockchain is immutable if it's replicated to multiple parties that have reasons not to collude. Most blockchain implementations guarantees that committed blocks are resistant to mutations if a majority of the participants (at least 50% of the participants) are honest. If an attacker manages to control >50% of the network then they have the ability to undo committed blocks. – Lie Ryan Sep 26 '16 at 11:05

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