This document explains a feature to facilitate debugging.
Starting from TFHE-rs 0.5, trivial ciphertexts introduce a new feature to facilitate debugging. This feature supports a debugger, print statements, and faster execution, significantly reducing waiting time and enhancing the development pace of FHE applications.
Trivial ciphertexts are not secure. An application released/deployed in production must never receive trivial ciphertext from a client.
To use this feature, simply call your circuits/functions with trivially encrypted values that are created using encrypt_trivial(instead of real encryptions that are created using encrypt):
use tfhe::prelude::*;
use tfhe::{set_server_key, generate_keys, ConfigBuilder, FheUint128};
fn mul_all(a: &FheUint128, b: &FheUint128, c: &FheUint128) -> FheUint128 {
// Use the debug format ('{:?}'), if you don't want to unwrap()
// and panic if the value is not a trivial.
println!(
"a: {:?}, b: {:?}, c: {:?}",
a.try_decrypt_trivial::<u128>(),
b.try_decrypt_trivial::<u128>(),
c.try_decrypt_trivial::<u128>(),
);
let tmp = a * b;
println!("a * b = {:?}", tmp.try_decrypt_trivial::<u128>());
tmp * c
}
fn main() {
let (cks, sks) = generate_keys(ConfigBuilder::default().build());
set_server_key(sks);
let a = FheUint128::encrypt_trivial(1234u128);
let b = FheUint128::encrypt_trivial(4567u128);
let c = FheUint128::encrypt_trivial(89101112u128);
// since all inputs are trivially encrypted, this is going to be
// much faster
let result = mul_all(&a, &b, &c);
}
This example is going to print:
a: Ok(1234), b: Ok(4567), c: Ok(89101112)
a * b = Ok(5635678)
If any input to mul_all is not a trivial ciphertexts, the computations will be done 100% in FHE, and the program will output:
a: Err(NotTrivialCiphertextError), b: Err(NotTrivialCiphertextError), c: Err(NotTrivialCiphertextError)
a * b = Err(NotTrivialCiphertextError)
Using trivial encryptions as input, the example runs in 980 ms on a standard 12-core laptop, compared to 7.5 seconds on a 128-core machine using real encryptions.