eval-function.py

from openfhe import *

## Sample Program: Step 1: Set CryptoContext

cc = BinFHEContext()
cc.GenerateBinFHEContext(STD128, True, 12)

## Sample Program: Step 2: Key Generation
# Generate the secret key
sk = cc.KeyGen()

print("Generating the bootstrapping keys...")

# Generate the bootstrapping keys (refresh and switching keys)
cc.BTKeyGen(sk)

print("Completed the key generation.")

## Sample Program: Step 3: Create the to-be-evaluated funciton and obtain its corresponding LUT
p = cc.GetMaxPlaintextSpace() # Obtain the maximum plaintext space

# Initialize Function f(x) = x^3 % p
def fp(m,p1):
    if m<p1:
        return m**3 % p1
    else: 
        return (m-p1//2)**3 % p1

# Generate LUT from function f(x)
lut = cc.GenerateLUTviaFunction(fp, p)

## Sample Program: Step 4: evalute f(x) homomorphically and decrypt
# Note that we check for all the possible plaintexts.
for i in range(p):
    ct1 = cc.Encrypt(sk, i % p, BINFHE_OUTPUT.LARGE_DIM, p)

    ct_cube = cc.EvalFunc(ct1, lut)

    result = cc.Decrypt(sk, ct_cube, p)

    print(f"input :{i}, expected :{fp(i, p)}, evaluated: {result}")