Some questions about BFV and BGV

[ypolyakov]

In BFV, the parameter selection logic is different. We find \log Q and the split it into maximum-size moduli, e.g., 60 bits. So 60 bits is the level of granularity (by default). This may leave a significant cushion (to accommodate another level). In BGV, the choice of parameters is more granular/tight. Each RNS modulus corresponds to one level, and there is no potential cushion for extra room. If you want to get more familiar with the differences of parameter selection between BFV and BGV, I suggest reading Revisiting Homomorphic Encryption Schemes for Finite Fields, e.g., Section 4 for BGV.