I want to extract all MSB with an RLWE Ciphertext into an vector.I I’m not sure if exist an solution.

I am not sure I understand your question. Could you please fix the grammatical errors in both the title and question.

OpenFHE includes `EvalSign`

(based on FHEW/TFHE) to find MSB of an LWE ciphertext. Are you asking whether such a capability exists for BGV or BFV?

If yes, then this can be achieved using BGV/BFV bootstrapping (more general case) or special polynomials. Please clarify your question so I could answer it more definitively.

Sorry,

Yes,My problem is that how to find MSB vector ciphertext of an RLWE ciphertext without decomposition.

The two potential solutions are:

- Logistic regression over encrypted data from fully homomorphic encryption (section 3.5)
- Faster homomorphic comparison operations for BGV and BFV

Alternatively, you use `EvalSign`

with scheme switching to/from FHEW/TFHE from/to BGV/BFV