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use super::CiphertextNoiseDegree;
use crate::core_crypto::algorithms::*;
use crate::core_crypto::entities::*;
use crate::shortint::atomic_pattern::AtomicPattern;
use crate::shortint::ciphertext::Degree;
use crate::shortint::server_key::{CheckError, GenericServerKey};
use crate::shortint::{Ciphertext, PaddingBit};
impl<AP: AtomicPattern> GenericServerKey<AP> {
/// Compute homomorphically a negation of a ciphertext.
///
/// This checks that the negation is possible. In the case where the carry buffers are full,
/// then it is automatically cleared to allow the operation.
///
/// 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;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 3;
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// let ct_res = sks.neg(&ct);
///
/// // Decrypt
/// let clear_res = cks.decrypt(&ct_res);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn neg(&self, ct: &Ciphertext) -> Ciphertext {
let mut ct_res = ct.clone();
self.neg_assign(&mut ct_res);
ct_res
}
/// Compute homomorphically a negation of a ciphertext.
///
/// This checks that the negation is possible. In the case where the carry buffers are full,
/// then it is automatically cleared to allow the operation.
///
/// 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;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 3;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// sks.neg_assign(&mut ct);
///
/// // Decrypt
/// let clear_res = cks.decrypt(&ct);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn neg_assign(&self, ct: &mut Ciphertext) {
if !ct.carry_is_empty() {
self.message_extract_assign(ct);
}
self.unchecked_neg_assign(ct);
self.message_extract_assign(ct);
}
/// Homomorphically negates a message without checks.
///
/// Negation here means the opposite value in the modulo set.
///
/// This function computes the opposite of a message without checking if it exceeds the
/// capacity of the ciphertext.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1;
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// let ct_res = sks.unchecked_neg(&ct);
///
/// // Decrypt
/// let three = cks.decrypt(&ct_res);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(modulus - msg, three);
/// ```
pub fn unchecked_neg(&self, ct: &Ciphertext) -> Ciphertext {
let mut result = ct.clone();
self.unchecked_neg_assign(&mut result);
result
}
pub fn unchecked_neg_with_correcting_term(&self, ct: &Ciphertext) -> (Ciphertext, u64) {
let mut result = ct.clone();
let z = self.unchecked_neg_assign_with_correcting_term(&mut result);
(result, z)
}
/// Homomorphically negates a message inplace without checks.
///
/// Negation here means the opposite value in the modulo set.
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 3;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// sks.unchecked_neg_assign(&mut ct);
///
/// // Decrypt
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(modulus - msg, cks.decrypt(&ct));
/// ```
pub fn unchecked_neg_assign(&self, ct: &mut Ciphertext) {
let _z = self.unchecked_neg_assign_with_correcting_term(ct);
}
pub fn unchecked_neg_assign_with_correcting_term(&self, ct: &mut Ciphertext) -> u64 {
// z = ceil( degree / 2^p ) * 2^p
let msg_mod = ct.message_modulus.0;
// Ensure z is always >= 1 (which would not be the case if degree == 0)
// some algorithms (e.g. overflowing_sub) require this even for trivial zeros
let mut z = ct.degree.get().div_ceil(msg_mod).max(1);
z *= msg_mod;
//Scaling + 1 on the padding bit
let w = self.encoding(PaddingBit::Yes).encode(Cleartext(z));
// (0,Delta*z) - ct
lwe_ciphertext_opposite_assign(&mut ct.ct);
lwe_ciphertext_plaintext_add_assign(&mut ct.ct, w);
// Update the degree
ct.degree = Degree::new(z);
z
}
/// Verify if a ciphertext can be negated.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 2;
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Check if we can perform a negation
/// sks.is_neg_possible(ct.noise_degree()).unwrap();
/// ```
pub fn is_neg_possible(&self, ct: CiphertextNoiseDegree) -> Result<(), CheckError> {
// z = ceil( degree / 2^p ) x 2^p
let msg_mod = self.message_modulus.0;
let mut z = ct.degree.get().div_ceil(msg_mod);
z = z.wrapping_mul(msg_mod);
self.max_degree.validate(Degree::new(z))
}
/// Compute homomorphically a negation of a ciphertext.
///
/// If the operation can be performed, the result is returned 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;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1;
///
/// // Encrypt a message
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation:
/// let ct_res = sks.checked_neg(&ct).unwrap();
///
/// let clear_res = cks.decrypt(&ct_res);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn checked_neg(&self, ct: &Ciphertext) -> Result<Ciphertext, CheckError> {
// If the ciphertext cannot be negated without exceeding the capacity of a ciphertext
self.is_neg_possible(ct.noise_degree())?;
let ct_result = self.unchecked_neg(ct);
Ok(ct_result)
}
/// Compute homomorphically a negation of a ciphertext.
///
/// If the operation is possible, the result is stored _in_ the input ciphertext.
/// Otherwise a [CheckError] is returned and the ciphertext is not .
///
///
///
/// # Example
///
/// ```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 1;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically the negation:
/// sks.checked_neg_assign(&mut ct).unwrap();
///
/// let clear_res = cks.decrypt(&ct);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn checked_neg_assign(&self, ct: &mut Ciphertext) -> Result<(), CheckError> {
self.is_neg_possible(ct.noise_degree())?;
self.unchecked_neg_assign(ct);
Ok(())
}
/// Compute homomorphically a negation of a ciphertext.
///
/// This checks that the negation 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;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 3;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// let ct_res = sks.smart_neg(&mut ct);
///
/// // Decrypt
/// let clear_res = cks.decrypt(&ct_res);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn smart_neg(&self, ct: &mut Ciphertext) -> Ciphertext {
// If the ciphertext cannot be negated without exceeding the capacity of a ciphertext
if self.is_neg_possible(ct.noise_degree()).is_err() {
self.message_extract_assign(ct);
}
self.is_neg_possible(ct.noise_degree()).unwrap();
self.unchecked_neg(ct)
}
/// Compute homomorphically a negation of a ciphertext.
///
/// This checks that the 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;
///
/// // Generate the client key and the server key:
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let msg = 3;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a negation
/// sks.smart_neg_assign(&mut ct);
///
/// // Decrypt
/// let clear_res = cks.decrypt(&ct);
/// let modulus = cks.parameters().message_modulus().0;
/// assert_eq!(clear_res, modulus - msg);
/// ```
pub fn smart_neg_assign(&self, ct: &mut Ciphertext) {
// If the ciphertext cannot be negated without exceeding the capacity of a ciphertext
if self.is_neg_possible(ct.noise_degree()).is_err() {
self.message_extract_assign(ct);
}
self.is_neg_possible(ct.noise_degree()).unwrap();
self.unchecked_neg_assign(ct);
}
}