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use super::CiphertextNoiseDegree;
use crate::core_crypto::algorithms::*;
use crate::core_crypto::entities::*;
use crate::shortint::ciphertext::Degree;
use crate::shortint::server_key::CheckError;
use crate::shortint::{Ciphertext, ServerKey};
impl ServerKey {
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// The result is returned in a _new_ ciphertext.
///
/// This function, like all "default" operations (i.e. not smart, checked or unchecked), will
/// check that the input ciphertext carries are empty and clears them if it's not the case and
/// the operation requires it. It outputs a ciphertext whose carry is always empty.
///
/// This means that when using only "default" operations, a given operation (like add for
/// example) has always the same performance characteristics from one call to another and
/// guarantees correctness by pre-emptively clearing carries of output ciphertexts.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1_u64;
/// let scalar = 9_u8;
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.scalar_add(&ct, scalar);
///
/// // The input ciphertext content is not changed
/// assert_eq!(cks.decrypt(&ct), msg);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct_res);
/// let modulus = cks.parameters.message_modulus().0 as u64;
/// assert_eq!((msg + scalar as u64) % modulus, clear);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.scalar_add(&ct, scalar);
///
/// // The input ciphertext content is not changed
/// assert_eq!(cks.decrypt(&ct), msg);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct_res);
/// let modulus = cks.parameters.message_modulus().0 as u64;
/// assert_eq!((msg + scalar as u64) % modulus, clear);
/// ```
pub fn scalar_add(&self, ct: &Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_res = ct.clone();
self.scalar_add_assign(&mut ct_res, scalar);
ct_res
}
/// Compute homomorphically an addition of a ciphertext by a scalar.
///
/// The result is _stored_ in the `ct` ciphertext.
///
/// This function, like all "default" operations (i.e. not smart, checked or unchecked), will
/// check that the input ciphertext carries are empty and clears them if it's not the case and
/// the operation requires it. It outputs a ciphertext whose carry is always empty.
///
/// This means that when using only "default" operations, a given operation (like add for
/// example) has always the same performance characteristics from one call to another and
/// guarantees correctness by pre-emptively clearing carries of output ciphertexts.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1_u64;
/// let scalar = 5_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.scalar_add_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct);
/// assert_eq!(
/// (msg + scalar as u64) % cks.parameters.message_modulus().0 as u64,
/// clear
/// );
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.scalar_add_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct);
/// assert_eq!(
/// (msg + scalar as u64) % cks.parameters.message_modulus().0 as u64,
/// clear
/// );
/// ```
pub fn scalar_add_assign(&self, ct: &mut Ciphertext, scalar: u8) {
let modulus = self.message_modulus.0 as u64;
let acc = self.generate_lookup_table(|x| (scalar as u64 + x) % modulus);
self.apply_lookup_table_assign(ct, &acc);
}
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// The result is returned in a _new_ ciphertext.
///
/// This function does _not_ check whether the capacity of the ciphertext is exceeded.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// let ct_res = sks.unchecked_scalar_add(&ct, 2);
///
/// let clear = cks.decrypt(&ct_res);
/// assert_eq!(3, clear);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// let ct_res = sks.unchecked_scalar_add(&ct, 2);
///
/// let clear = cks.decrypt(&ct_res);
/// assert_eq!(3, clear);
/// ```
pub fn unchecked_scalar_add(&self, ct: &Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_result = ct.clone();
self.unchecked_scalar_add_assign(&mut ct_result, scalar);
ct_result
}
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// The result it stored in the given ciphertext.
///
/// This function does not check whether the capacity of the ciphertext is exceeded.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// sks.unchecked_scalar_add_assign(&mut ct, 2);
///
/// let clear = cks.decrypt(&ct);
/// assert_eq!(3, clear);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// sks.unchecked_scalar_add_assign(&mut ct, 2);
///
/// let clear = cks.decrypt(&ct);
/// assert_eq!(3, clear);
/// ```
pub fn unchecked_scalar_add_assign(&self, ct: &mut Ciphertext, scalar: u8) {
let delta = (1_u64 << 63) / (self.message_modulus.0 * self.carry_modulus.0) as u64;
let shift_plaintext = u64::from(scalar) * delta;
let encoded_scalar = Plaintext(shift_plaintext);
lwe_ciphertext_plaintext_add_assign(&mut ct.ct, encoded_scalar);
ct.degree = Degree::new(ct.degree.get() + scalar as usize);
}
/// Verify if a scalar can be added to the ciphertext.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(2);
///
/// // Verification if the scalar addition can be computed:
/// sks.is_scalar_add_possible(ct.noise_degree(), 3).unwrap();
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(2);
///
/// // Verification if the scalar addition can be computed:
/// sks.is_scalar_add_possible(ct.noise_degree(), 3).unwrap();
/// ```
pub fn is_scalar_add_possible(
&self,
ct: CiphertextNoiseDegree,
scalar: u8,
) -> Result<(), CheckError> {
let final_degree = scalar as usize + ct.degree.get();
self.max_degree.validate(Degree::new(final_degree))
}
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// If the operation is possible, the result is returned in a _new_ ciphertext.
/// Otherwise a [CheckError] is returned.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(1);
///
/// // Compute homomorphically a addition multiplication:
/// let ct_res = sks.checked_scalar_add(&ct, 2).unwrap();
///
/// let clear_res = cks.decrypt(&ct_res);
/// assert_eq!(clear_res, 3);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let ct = cks.encrypt(1);
///
/// // Compute homomorphically a addition multiplication:
/// let ct_res = sks.checked_scalar_add(&ct, 2).unwrap();
///
/// let clear_res = cks.decrypt(&ct_res);
/// assert_eq!(clear_res, 3);
/// ```
pub fn checked_scalar_add(
&self,
ct: &Ciphertext,
scalar: u8,
) -> Result<Ciphertext, CheckError> {
//If the ciphertext cannot be multiplied without exceeding the max degree
self.is_scalar_add_possible(ct.noise_degree(), scalar)?;
let ct_result = self.unchecked_scalar_add(ct, scalar);
Ok(ct_result)
}
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// If the operation is possible, the result is stored _in_ the input ciphertext.
/// Otherwise a [CheckError] is returned and the ciphertext is not
/// modified.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// sks.checked_scalar_add_assign(&mut ct, 2).unwrap();
///
/// let clear_res = cks.decrypt(&ct);
/// assert_eq!(clear_res, 3);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(1);
///
/// // Compute homomorphically a scalar addition:
/// sks.checked_scalar_add_assign(&mut ct, 2).unwrap();
///
/// let clear_res = cks.decrypt(&ct);
/// assert_eq!(clear_res, 3);
/// ```
pub fn checked_scalar_add_assign(
&self,
ct: &mut Ciphertext,
scalar: u8,
) -> Result<(), CheckError> {
self.is_scalar_add_possible(ct.noise_degree(), scalar)?;
self.unchecked_scalar_add_assign(ct, scalar);
Ok(())
}
/// Compute homomorphically an addition between a ciphertext and a scalar.
///
/// The result is returned in a _new_ ciphertext.
///
/// This checks that the scalar addition is possible. In the case where the carry buffers are
/// full, then it is automatically cleared to allow the operation.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1_u64;
/// let scalar = 9_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.smart_scalar_add(&mut ct, scalar);
///
/// // The input ciphertext content is not changed
/// assert_eq!(cks.decrypt(&ct), msg);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct_res);
/// let modulus = cks.parameters.message_modulus().0 as u64;
/// assert_eq!(2, clear % modulus);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.smart_scalar_add(&mut ct, scalar);
///
/// // The input ciphertext content is not changed
/// assert_eq!(cks.decrypt(&ct), msg);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct_res);
/// let modulus = cks.parameters.message_modulus().0 as u64;
/// assert_eq!(2, clear % modulus);
/// ```
#[allow(clippy::needless_pass_by_ref_mut)]
pub fn smart_scalar_add(&self, ct: &mut Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_result = ct.clone();
self.smart_scalar_add_assign(&mut ct_result, scalar);
ct_result
}
/// Compute homomorphically an addition of a ciphertext by a scalar.
///
/// The result is _stored_ in the `ct` ciphertext.
///
/// This checks that the scalar addition is possible. In the case where the carry buffers are
/// full, then it is automatically cleared to allow the operation.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::{
/// PARAM_MESSAGE_2_CARRY_2_KS_PBS, PARAM_MESSAGE_2_CARRY_2_PBS_KS,
/// };
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1_u64;
/// let scalar = 5_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.smart_scalar_add_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// let clear = cks.decrypt_message_and_carry(&ct);
/// assert_eq!(6, clear);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.smart_scalar_add_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// let clear = cks.decrypt_message_and_carry(&ct);
/// assert_eq!(6, clear);
/// ```
pub fn smart_scalar_add_assign(&self, ct: &mut Ciphertext, scalar: u8) {
// Direct scalar computation is possible
if self
.is_scalar_add_possible(ct.noise_degree(), scalar)
.is_ok()
{
self.unchecked_scalar_add_assign(ct, scalar);
} else {
// If the scalar is too large, PBS is used to compute the scalar mul
let acc = self.generate_msg_lookup_table(|x| scalar as u64 + x, self.message_modulus);
self.apply_lookup_table_assign(ct, &acc);
ct.degree = Degree::new(self.message_modulus.0 - 1);
}
}
}