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Comment by DoofusOfDeath | Hacker News Reader

Is a trapdoor the same as a backdoor?

No. Neither is it an error in the article, since they use the same term in their paper:

https://people.eng.unimelb.edu.au/vjteague/UniversalVerifiab...

It seems there is a class of commitment schemes that's called "trapdoor commitment schemes" and deployed in SwissPost. I'm not aware of these, but they cite this PhD thesis on the topic:

https://www.math.uni-frankfurt.de/~dmst/research/phdtheses/m...

(Disclaimer: I have no idea how these work - maybe the authors mixed up their terminology ;-))

A trapdoor is something that's hard to invert: https://en.m.wikipedia.org/wiki/Trapdoor_function

A backdoor is a hidden access, like this.

Just a mistake in the article.

I don't think it's a mistake. I think this is actually a trapdoor in the cryptographic sense of the term, and the security hole is the result of them using a zero-knowledge proof scheme based on these kind of trapdoor functions that relies on no-one having a copy of the trapdoor information, but incorrectly letting the untrusted party choose the trapdoor function.

No mistake. It's a trapdoor.

Trapdoor is an older term that means the same thing as "backdoor". I think this author chose to use it in order to distinguish between the modern colloquial meaning of "backdoor" as "a method for an attack to eavesdrop on communication", and the more abstract meaning of a correctness vulnerability in an allegedly secure counting algorithm.

Yes. The Jargon File[1] lists it as a synonym, though note that Wikipedia[2] calls this usage outdated.

[1] http://catb.org/jargon/html/T/trap-door.html

[2] https://en.wikipedia.org/wiki/Trapdoor_(disambiguation)

No, it's clear that the researchers are using the term trapdoor in a technical sense. Specifically, one of the key ideas in the swiss system is that it produce a proof that the votes produced as the result of the "shuffle" operation have the same meaning as the votes that are provided as inputs. The easiest "proof" of this would simply be to publish the input votes... but that would defeat the whole purpose of the shuffling. Instead, the Swiss system appears to involve a trapdoor commitment that produces a non-reversible token (hence "trapdoor") that could only be generated if this is a legitimate shuffling. As I read it, this is much like (for instance) a SHA-256 hash of an input message that can be generated to ensure that a document has not been tampered with.

According to the article it certainly reads that way.

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