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use crate::server_key::CheckError;
use crate::server_key::CheckError::CarryFull;
use crate::{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 concrete_integer::gen_keys;
/// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(&PARAM_MESSAGE_2_CARRY_2);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.unchecked_crt_scalar_mul_assign(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt_crt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % 30, 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()) {
self.key
.unchecked_scalar_mul_assign(ct_i, (scalar % mod_i) as u8);
}
}
///Verifies if ct1 can be multiplied by scalar.
///
/// # Example
///
///```rust
/// use concrete_integer::gen_keys;
/// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(&PARAM_MESSAGE_2_CARRY_2);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// let tmp = sks.is_crt_scalar_mul_possible(&mut ctxt_1, clear_2);
///
/// assert_eq!(true, tmp);
/// ```
pub fn is_crt_scalar_mul_possible(&self, ctxt: &CrtCiphertext, scalar: u64) -> bool {
for (ct_i, mod_i) in ctxt.blocks.iter().zip(ctxt.moduli.iter()) {
if !self
.key
.is_scalar_mul_possible(ct_i, (scalar % mod_i) as u8)
{
return false;
}
}
true
}
/// 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 [CheckError::CarryFull] is returned.
///
/// # Example
///
/// ```rust
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// use concrete_integer::gen_keys;
/// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(&PARAM_MESSAGE_2_CARRY_2);
///
/// let clear_1 = 14;
/// let clear_2 = 2;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.checked_crt_scalar_mul_assign(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt_crt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % 30, res);
/// # Ok(())
/// # }
/// ```
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
if self.is_crt_scalar_mul_possible(ct, scalar) {
ct_result = self.unchecked_crt_scalar_mul(&ct_result, scalar);
Ok(ct_result)
} else {
Err(CarryFull)
}
}
/// 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 [CheckError::CarryFull] 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
if self.is_crt_scalar_mul_possible(ct, scalar) {
self.unchecked_crt_scalar_mul_assign(ct, scalar);
Ok(())
} else {
Err(CarryFull)
}
}
/// 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_2_CARRY_2,
/// the scalar should fit in 2 bits.
///
/// The result is returned as a new ciphertext.
///
/// # Example
///
///```rust
/// use concrete_integer::gen_keys;
/// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(&PARAM_MESSAGE_2_CARRY_2);
///
/// let clear_1 = 14;
/// let clear_2 = 14;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// let ctxt = sks.smart_crt_scalar_mul(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt_crt(&ctxt);
/// assert_eq!((clear_1 * clear_2) % 30, res);
/// ```
pub fn smart_crt_scalar_mul(&self, ctxt: &mut CrtCiphertext, scalar: u64) -> CrtCiphertext {
if !self.is_crt_scalar_mul_possible(ctxt, scalar) {
self.full_extract(ctxt);
}
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_2_CARRY_2,
/// the scalar should fit in 2 bits.
///
/// The result is assigned to the input ciphertext
///
/// # Example
///
///```rust
/// use concrete_integer::gen_keys;
/// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(&PARAM_MESSAGE_2_CARRY_2);
///
/// let clear_1 = 14;
/// let clear_2 = 14;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.smart_crt_scalar_mul_assign(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt_crt(&ctxt_1);
/// assert_eq!((clear_1 * clear_2) % 30, res);
/// ```
pub fn smart_crt_scalar_mul_assign(&self, ctxt: &mut CrtCiphertext, scalar: u64) {
if !self.is_crt_small_scalar_mul_possible(ctxt, scalar) {
self.full_extract(ctxt);
}
self.unchecked_crt_scalar_mul_assign(ctxt, scalar);
}
pub fn is_crt_small_scalar_mul_possible(&self, ctxt: &CrtCiphertext, scalar: u64) -> bool {
for ct_i in ctxt.blocks.iter() {
if !self.key.is_scalar_mul_possible(ct_i, scalar as u8) {
return false;
}
}
true
}
}