Bootstrap functionality: There are three methods that have to be called in this specific order:
EvalBootstrapSetup: computes and encodes the coefficients for encoding and decoding and stores the necessary parameters
EvalBootstrapKeyGen: computes and stores the keys for rotations and conjugation
EvalBootstrap: refreshes the given ciphertext Sets all parameters for the linear method for the FFT-like method
Parameters
levelBudget – - vector of budgets for the amount of levels in encoding and decoding
dim1 – - vector of inner dimension in the baby-step giant-step routine for encoding and decoding
slots – - number of slots to be bootstrapped
correctionFactor – - value to rescale message by to improve precision. If set to 0, we use the default logic. This value is only used when NATIVE_SIZE=64
precompute – - flag specifying whether to precompute the plaintexts for encoding and decoding.
Virtual function to define the generation of all automorphism keys for EvalBT (with FFT evaluation). EvalBTKeyGen uses the baby-step/giant-step strategy.
Defines the bootstrapping evaluation of ciphertext
The flavor of bootstrapping that uses the numIterations and precision parameters is described in the Meta-BTS paper. Source: Bae Y., Cheon J., Cho W., Kim J., and Kim T. META-BTS: Bootstrapping Precision Beyond the Limit. Cryptology ePrint Archive, Report 2022/1167. (https://eprint.iacr.org/2022/1167.pdf)
Parameters
ciphertext – the input ciphertext.
numIterations – number of iterations to run iterative bootstrapping (Meta-BTS). Increasing the iterations increases the precision of bootstrapping.
precision – precision of initial bootstrapping algorithm. This value is determined by the user experimentally by first running EvalBootstrap with numIterations = 1 and precision = 0 (unused).