oprf protocol for privacy intersection

[hdkoutann]

Hello, I want to use the oprf protocol for privacy intersection, but I still don’t know how to use it after reading the code. Is there any detailed explanation document that I can refer to? Thanks

[pvriel]

Hi! Unfortunately, there's no in-depth documentation due to a lack of time. Can you maybe explain the problem more specifically? I can help you if you want.

[hdkoutann]

Is the default value corresponding to the KISS17ObliviousTransferDefaultValues object in the code fixed? Does it need to change with every interaction?

[pvriel]

The KISS17ObliviousTransferDefaultValues class was only introduced for testing purposes; I knew the parameters, input & output in advance and double-checked if my code generated the correct output itself.
The names of the parameters refer to the KISS17 PSI paper. I don't have time now to look up the paper, but if you replace the 'q' with an 'l', you can also check: https://en.wikipedia.org/wiki/Naor%E2%80%93Reingold_pseudorandom_function

I don't have time now, but I'll try to update the documentation this weekend.

[hdkoutann]

Sorry, I have a question to ask you.
My current requirement is that the C side has data X; the S side has data Y, and I want to find the intersection of X and Y through the OPRF protocol;
I have now implemented this function through your code, but since all the code is in the Test class; I now want to separate the code logic on the C side from the code logic on the S side; because I don’t understand the data interaction process very well, I can’t Know which logic should be on the S side and which logic should be on the C side; how the data between them interacts; please guide!

[pvriel]

The code is designed to closely resemble my other project https://github.com/pvriel/PRF4J.
For your specific case (PSI), one party (let's say the S-side) first needs to calculate PRF(Y, k) = Y_PRF with his own private input Y and PRF key k. This is something you can do with the library I just mentioned.
For the next step (the C-side calculating OPRF(X) = PRF(X, k) = X_PRF), take a look at https://github.com/pvriel/oprf4j/tree/main/src/main/java/com/github/pvriel/oprf4j/nroprf/semihonest. There are two implementations of the OPRF protocol there. In the example here, the S-side will be the 'provider', since he has the key. The C-side will be the evaluator. These two might share some constructor parameters (cf. documentation) but besides that, they don't need to be intertwined. Just make sure for the Input- and Outputstreams that are used in the code that: output 1 --> input 2 & output 2 --> input 1.

Does this help?

[pvriel]

Also note: these are semi-honest implementations.