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Evaluate sign on an encrypted value (functional bootstrapping)

Source: R/binfhe.R
eval_sign.Rd

Extracts the most-significant bit of an LWE ciphertext encrypted under the large modulus Q. The context must have been created with arb_func = TRUE.

Usage

eval_sign(ctx, ct, scheme_switch = FALSE)

Arguments

ctx

A BinFHE context built with arb_func = TRUE

ct

An LWECiphertext encrypted via bin_encrypt(..., mod = Q)

scheme_switch

Logical; when TRUE, the output ciphertext is encoded compatibly with the CKKS<->FHEW scheme-switching pipeline (the schemeSwitch flag at binfhecontext.h line 367). Default FALSE for the standalone FHEW path. Per the upstream header description, this is the "flag that indicates if it should be compatible to scheme switching".

Value

An LWECiphertext encrypting 0 if the input was negative (i.e. lay in the upper half of [0, Q)), 1 otherwise