What are the r and rInv values for?

[nicolai-huening]

Hello together,
I have a question regarding the 'r' and 'rInv' values. I do not understand what part thees values play in the overall protocol. First I thought it is used for a kind of FHE-Offline-phase (As described here), but neither 'r' nor 'rInv' are used by klyshko, only by ephemeral and amphora.
As far as I can tell the r and rInv are inverse mod p, and they are used only on the shares of secrets. Is this done to ensure security during the communication between amphora and the client?

Thanks a lot in advance
Nicolai

[sbckr]

Hi @nicolai-huening.

r and rInv are used for conversion between BigInteger and Montgomery Representation as used by MP-SPDZ to speed up computation.
See mp-spdz-integration for more details on how they are used internally.

Best regards
Sebastian

[sbckr]

@nicolai-huening

By the way, thank you and congratulations for the first question in our organization's discussion space.

🥳🪅🍾

[nicolai-huening]

Thank you very much, that was the puzzle pease I was missing! 😄