eval_fbt_setup: CKKS functional bootstrapping of a look-up table

In openfhe.R: R Interface to the 'OpenFHE' Fully Homomorphic Encryption Library

CKKS functional bootstrapping of a look-up table

Description

Functional bootstrapping refreshes a ciphertext and applies a look-up table to the encrypted integers in the same step. The input is an RLWE ciphertext converted to CKKS with schemelet_convert_rlwe_to_ckks(), and the output goes back with schemelet_convert_ckks_to_rlwe().

Usage

eval_fbt_setup(
  cc,
  coeffs,
  num_slots,
  p_in,
  p_out,
  big_q,
  pub_key,
  dim1,
  level_budget,
  lvls_after_boot = 0L,
  depth_leveled_computation = 0L,
  order = 1L
)

eval_fbt(
  ct,
  coeffs,
  digit_bit_size,
  initial_scaling,
  post_scaling,
  level_to_reduce = 0L,
  order = 1L
)

eval_fbt_no_decoding(ct, coeffs, digit_bit_size, initial_scaling, order = 1L)

eval_hom_decoding(ct, post_scaling, level_to_reduce = 0L)

Arguments

cc	A CKKS CryptoContext with Feature$FHE enabled.
coeffs	The coefficients of the look-up table; see Details.
num_slots	Integer; number of CKKS slots.
p_in, p_out	Input and output plaintext moduli.
big_q	The modulus of the RLWE ciphertext converted to CKKS.
pub_key	The PublicKey.
dim1	Integer vector of length 2; baby-step dimensions of the two linear transforms (0 for the library's choice).
level_budget	Integer vector of length 2; level budgets of the two linear transforms.
lvls_after_boot	Integer; levels available after bootstrapping. Default 0L.
depth_leveled_computation	Integer; levels of the computation done between eval_fbt_no_decoding() (or eval_mvb_no_decoding()) and eval_hom_decoding(). Default 0L.
order	Integer; order of the Hermite interpolation. Default 1L.
ct	A Ciphertext.
digit_bit_size	Integer; number of bits of the input modulus.
initial_scaling	The modulus the input is scaled by, usually get_modulus() of the element parameters from schemelet_get_element_params().
post_scaling	The scale applied to the coefficients (the scale of get_hermite_trig_coefficients()), undone here.
level_to_reduce	Integer; levels to drop before decoding. Default 0L.

Details

eval_fbt_setup() prepares the context; call eval_bootstrap_key_gen() and eval_mult_key_gen() after it. eval_fbt() applies the table. eval_fbt_no_decoding() stops before the return to coefficient encoding, leaving a slot-packed CKKS ciphertext on which leveled operations can be done; eval_hom_decoding() then finishes.

The R type of coeffs selects the form of the table, as the Python type does in openfhe-python. An integer vector is the optimized Boolean case (input modulus 2, order 1), with the two coefficients c(f(1), f(0) - f(1)); build it with as.integer(). A double or complex vector is the general case, with the coefficients from get_hermite_trig_coefficients().

p_in, p_out, big_q, initial_scaling and post_scaling are strings of decimal digits, or whole numbers of at most 2^53.

Value

eval_fbt_setup(): cc, invisibly. The others: a Ciphertext.

See Also

eval_mvb_precompute() to apply several tables to one input; get_fbt_depth().

openfhe.R documentation built on Nov. 13, 2026, 5:07 p.m.