4 ms·

In the Waldo example, if Bob has watermarked the back of the puzzle and Alice shows him the cutout Waldo, what prevents Bob from comparing the portion of the wa

by dcow 5y ago

In the Waldo example, if Bob has watermarked the back of the puzzle and Alice shows him the cutout Waldo, what prevents Bob from comparing the portion of the watermark on the back of the cutout Waldo (provided by Alice) with the original watermark (say Bob chose the watermark to be a grid of cells where each cell is trivially identifiable and small enough to be contained on the back of the cutout), thus deriving Waldo’s location?

jtsiskin 5y ago
Alice should properly reject that proposal, and only accept pages with totally uniform watermarks.
- dcow 5y ago
  So in essence, Alice must also verify that, for any given puzzle, it has been constructed in a way such that Bob cannot discern the information that is intended to be private? That sounds problematic for general public Alice and clever trickster Bob scenarios, which I suspect would be a common use case. What’s the solution, an oligopoly of Proof Authorities?
  - wutbrodo 5y ago
    > That sounds problematic for general public Alice and clever trickster Bob scenarios, which I suspect would be a common use case. The general public isn't involved in constructing the proofs, just as they don't manually engage in cryptographic exchanges of any kind. Absent cryptographic expertise, the general public is forced to delegate their trust to cryptographic experts, whose code they execute when making exchanges with tricksters.
    - dcow 5y ago
      Sounds like you are saying ZKPs won’t be generally applicable and instead that these proofs have to be specifically crafted for a given application use case much like how you choose an acceptable cipher suite today? Like I go to website A and they want me to authenticate that I have access to a unique email address without revealing which one and they offer a zkp-email-ident challenge, I’d have to use OpenZKP which supports zkp-email-ident because the cryptography community vetted it and thus it’s included as a supported auth challenge? So the implication here would be that the protocol specifies the exact nature of the (back to the cutout example) image such that it’s impossible for Bob to apply an adversarial watermark? So generally ZKPs are more like a cryptography primitive and protocols must be developed that apply them in ways that mitigate adversaries.

by dcow 5y ago

jtsiskin 5y ago

Alice should properly reject that proposal, and only accept pages with totally uniform watermarks.

dcow 5y ago
So in essence, Alice must also verify that, for any given puzzle, it has been constructed in a way such that Bob cannot discern the information that is intended to be private? That sounds problematic for general public Alice and clever trickster Bob scenarios, which I suspect would be a common use case. What’s the solution, an oligopoly of Proof Authorities?
- wutbrodo 5y ago
  > That sounds problematic for general public Alice and clever trickster Bob scenarios, which I suspect would be a common use case. The general public isn't involved in constructing the proofs, just as they don't manually engage in cryptographic exchanges of any kind. Absent cryptographic expertise, the general public is forced to delegate their trust to cryptographic experts, whose code they execute when making exchanges with tricksters.
  - dcow 5y ago
    Sounds like you are saying ZKPs won’t be generally applicable and instead that these proofs have to be specifically crafted for a given application use case much like how you choose an acceptable cipher suite today? Like I go to website A and they want me to authenticate that I have access to a unique email address without revealing which one and they offer a zkp-email-ident challenge, I’d have to use OpenZKP which supports zkp-email-ident because the cryptography community vetted it and thus it’s included as a supported auth challenge? So the implication here would be that the protocol specifies the exact nature of the (back to the cutout example) image such that it’s impossible for Bob to apply an adversarial watermark? So generally ZKPs are more like a cryptography primitive and protocols must be developed that apply them in ways that mitigate adversaries.