As explained in their example here, Microsoft Seal uses a special modulus that is used for all key material like relinearization key. I wanted to ask why special modulus is used?

  • $\begingroup$ Found a concrete reason for that extra moduli , in appendix B of this paper they give overview of key-switching techniques eprint.iacr.org/2020/1203.pdf , basically they perform a modulus switch after key-switch to reduce the added noise. For this mod-switch they start with q'q and switch back to q (Ciphertext modulus). Same paper also talks about another decomposition based key-switching technique and Seal implements a hybrid approach using both techniques $\endgroup$
    – LWE-13
    May 27 at 2:56


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