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use crate::integer::server_key::CheckError;
use crate::integer::{CrtCiphertext, ServerKey};
impl ServerKey {
/// Computes homomorphically a multiplication between a scalar and a ciphertext.
///
/// This function computes the operation without checking if it exceeds the capacity of the
/// ciphertext.
///
/// The result is returned as a new ciphertext.
///
/// # Example
///
///```rust
/// use tfhe::integer::gen_keys_crt;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128;
///
/// // Generate the client key and the server key:
/// let basis = vec![2, 3, 5];
/// let modulus: u64 = basis.iter().product();
/// let (cks, sks) = gen_keys_crt(PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128, basis);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt(clear_1);
///
/// sks.unchecked_crt_scalar_mul_assign(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % modulus, res);
/// ```
pub fn unchecked_crt_scalar_mul(&self, ctxt: &CrtCiphertext, scalar: u64) -> CrtCiphertext {
let mut ct_result = ctxt.clone();
self.unchecked_crt_scalar_mul_assign(&mut ct_result, scalar);
ct_result
}
pub fn unchecked_crt_scalar_mul_assign(&self, ctxt: &mut CrtCiphertext, scalar: u64) {
for (ct_i, mod_i) in ctxt.blocks.iter_mut().zip(ctxt.moduli.iter()) {
let scalar_i = (scalar % mod_i) as u8;
if self
.key
.max_degree
.validate(ct_i.degree * u64::from(scalar_i))
.is_ok()
&& self
.key
.max_noise_level
.validate(ct_i.noise_level() * scalar)
.is_ok()
{
self.key.unchecked_scalar_mul_assign(ct_i, scalar_i);
} else {
self.key
.unchecked_scalar_mul_lsb_small_carry_modulus_assign(ct_i, scalar_i);
}
}
}
///Verifies if ct1 can be multiplied by scalar.
///
/// # Example
///
///```rust
/// use tfhe::integer::gen_keys_crt;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128;
///
/// // Generate the client key and the server key:
/// let basis = vec![2, 3, 5];
/// let (cks, sks) = gen_keys_crt(PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128, basis);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// // Encrypt two messages
/// let ctxt_1 = cks.encrypt(clear_1);
///
/// sks.is_crt_scalar_mul_possible(&ctxt_1, clear_2).unwrap();
/// ```
pub fn is_crt_scalar_mul_possible(
&self,
ctxt: &CrtCiphertext,
scalar: u64,
) -> Result<(), CheckError> {
for (ct_i, mod_i) in ctxt.blocks.iter().zip(ctxt.moduli.iter()) {
self.key
.is_scalar_mul_possible(ct_i.noise_degree(), (scalar % mod_i) as u8)?;
}
Ok(())
}
/// Computes homomorphically a multiplication between a scalar and a ciphertext.
///
/// If the operation can be performed, the result is returned in a new ciphertext.
/// Otherwise a [CheckError] is returned.
///
/// # Example
///
/// ```rust
/// use tfhe::integer::gen_keys_crt;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128;
///
/// // Generate the client key and the server key:
/// let basis = vec![2, 3, 5];
/// let modulus: u64 = basis.iter().product();
/// let (cks, sks) = gen_keys_crt(PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128, basis);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt(clear_1);
///
/// sks.checked_crt_scalar_mul_assign(&mut ctxt_1, clear_2)
/// .unwrap();
///
/// // Decrypt
/// let res = cks.decrypt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % modulus, res);
/// ```
pub fn checked_crt_scalar_mul(
&self,
ct: &CrtCiphertext,
scalar: u64,
) -> Result<CrtCiphertext, CheckError> {
let mut ct_result = ct.clone();
// If the ciphertext cannot be multiplied without exceeding the capacity of a ciphertext
self.is_crt_scalar_mul_possible(ct, scalar)?;
ct_result = self.unchecked_crt_scalar_mul(&ct_result, scalar);
Ok(ct_result)
}
/// Computes homomorphically a multiplication between a scalar and a ciphertext.
///
/// If the operation can be performed, the result is assigned to the ciphertext given
/// as parameter.
/// Otherwise a [CheckError] is returned.
pub fn checked_crt_scalar_mul_assign(
&self,
ct: &mut CrtCiphertext,
scalar: u64,
) -> Result<(), CheckError> {
// If the ciphertext cannot be multiplied without exceeding the capacity of a ciphertext
self.is_crt_scalar_mul_possible(ct, scalar)?;
self.unchecked_crt_scalar_mul_assign(ct, scalar);
Ok(())
}
/// Computes homomorphically a multiplication between a scalar and a ciphertext.
///
/// `small` means the scalar value shall fit in a __shortint block__.
/// For example, if the parameters are PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128,
/// the scalar should fit in 2 bits.
///
/// The result is returned as a new ciphertext.
///
/// # Example
///
///```rust
/// use tfhe::integer::gen_keys_crt;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128;
///
/// // Generate the client key and the server key:
/// let basis = vec![2, 3, 5];
/// let modulus: u64 = basis.iter().product();
/// let (cks, sks) = gen_keys_crt(PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128, basis);
///
/// let clear_1 = 14;
/// let clear_2 = 14;
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt(clear_1);
///
/// let ctxt = sks.smart_crt_scalar_mul(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ctxt);
/// assert_eq!((clear_1 * clear_2) % modulus, res);
/// ```
pub fn smart_crt_scalar_mul(&self, ctxt: &mut CrtCiphertext, scalar: u64) -> CrtCiphertext {
if self.is_crt_scalar_mul_possible(ctxt, scalar).is_err() {
self.full_extract_message_assign(ctxt);
}
self.is_crt_scalar_mul_possible(ctxt, scalar).unwrap();
self.unchecked_crt_scalar_mul(ctxt, scalar)
}
/// Computes homomorphically a multiplication between a scalar and a ciphertext.
///
/// `small` means the scalar shall value fit in a __shortint block__.
/// For example, if the parameters are PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128,
/// the scalar should fit in 2 bits.
///
/// The result is assigned to the input ciphertext
///
/// # Example
///
///```rust
/// use tfhe::integer::gen_keys_crt;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128;
///
/// // Generate the client key and the server key:
/// let basis = vec![2, 3, 5];
/// let modulus: u64 = basis.iter().product();
/// let (cks, sks) = gen_keys_crt(PARAM_MESSAGE_3_CARRY_3_KS_PBS_GAUSSIAN_2M128, basis);
///
/// let clear_1 = 14;
/// let clear_2 = 14;
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt(clear_1);
///
/// sks.smart_crt_scalar_mul_assign(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % modulus, res);
/// ```
pub fn smart_crt_scalar_mul_assign(&self, ctxt: &mut CrtCiphertext, scalar: u64) {
if self.is_crt_small_scalar_mul_possible(ctxt, scalar).is_err() {
self.full_extract_message_assign(ctxt);
}
self.is_crt_scalar_mul_possible(ctxt, scalar).unwrap();
self.unchecked_crt_scalar_mul_assign(ctxt, scalar);
}
pub fn is_crt_small_scalar_mul_possible(
&self,
ctxt: &CrtCiphertext,
scalar: u64,
) -> Result<(), CheckError> {
for ct_i in ctxt.blocks.iter() {
self.key
.is_scalar_mul_possible(ct_i.noise_degree(), scalar as u8)?;
}
Ok(())
}
}