Hello,
I am trying to extract a LWE ciphertext from a RLWE ciphertext yet at the decryption of the LWE ciphertext I obtain random values. I use concrete core. Here is the code :
use concrete_core::prelude::{GlweCiphertextCount, GlweDimension, PolynomialSize, Variance, LweCiphertext64,*};
use concrete_core::specification::engines::{
LweCiphertextDiscardingExtractionEngine, LweCiphertextDiscardingExtractionError,
};
use std::error::Error;
fn main() -> Result<(), Box<dyn Error>> {
// DISCLAIMER: the parameters used here are only for test purpose, and are not secure.
let glwe_dimension = GlweDimension(2);
let polynomial_size = PolynomialSize(4);
let lwe_dimension = LweDimension(8);
//obtaining my input from a txt file and shifting by 20 bits
let input = get_input_from_txt("input.txt");
let input = shift_input(input);
let noise = Variance(2_f64.powf(-75.));
// Unix seeder must be given a secret input.
// Here we just give it 0, which is totally unsafe.
const UNSAFE_SECRET: u128 = 0;
let mut engine = DefaultEngine::new(Box::new(UnixSeeder::new(UNSAFE_SECRET)))?;
let key: GlweSecretKey32 = engine.generate_new_glwe_secret_key(glwe_dimension, polynomial_size)?;
let plaintext = engine.create_plaintext_vector_from(&input)?;
let ciphertext = engine.encrypt_glwe_ciphertext(&key, &plaintext, noise)?;
let lwe_key : LweSecretKey32 = engine.generate_new_lwe_secret_key(lwe_dimension)?;
let mut lwe_ciphertext = engine.zero_encrypt_lwe_ciphertext(&lwe_key,noise)?;
engine.discard_extract_lwe_ciphertext( &mut lwe_ciphertext, &ciphertext,MonomialIndex(2));
let decrypted_plaintext2 = engine.decrypt_lwe_ciphertext(&lwe_key, &lwe_ciphertext)?;
let output: u32 = engine.retrieve_plaintext(&decrypted_plaintext2)?;
println!("{}",output>>20);
Ok(())
}
I would like to know if I am using the good function (discard_extract_lwe_ciphertext) and in this case what shall I correct. Else I would like to know if there is a function to extract a LWE ciphertext from a RLWE ciphertext.
Thank you for your answer
