Do Large Precision Comparison have any relevant reference papers？Can the current threshold version of CKKS be used for scheme switching FHEW and comparison?
AFAIK
- FHEW/TFHE: using “programmable bootstrapping” (https://eprint.iacr.org/2021/1337.pdf)
- CKKS: using polynomial approximations of the sign function (Optimization of Homomorphic Comparison Algorithm on RNS-CKKS Scheme)
The large precision comparison logic implemented in OpenFHE is described in https://eprint.iacr.org/2021/1337.pdf, as @narger wrote.
The scheme switching is not currently implemented in OpenFHE for the threshold case. While you can thresholdize the scheme switching/comparison key generation part for CKKS in OpenFHE, the library does not currently support threshold FHEW (scheme switching also needs a FHEW secret key and bootstrapping key). Threshold FHEW will be added to OpenFHE in the future.
So can the threshold version of CKKS be converted to scheme FHEW? Is it not possible?
It is possible, but it is still an active area of research to obtain efficient threshold FHEW. The reason for that is that the noise flooding required for threshold security leads to a growth of the ciphertext modulus as compared to the single-party version, and the performance of FHEW is much more sensitive to large moduli compared to BGV/CKKS.