1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536
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 a multiplication of a ciphertext by a scalar.
///
/// 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 = 3_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.scalar_mul(&mut ct, scalar);
///
/// // 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 mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.scalar_mul(&mut ct, scalar);
///
/// // 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_mul(&self, ct: &Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_res = ct.clone();
self.scalar_mul_assign(&mut ct_res, scalar);
ct_res
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// 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 = 3_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.scalar_mul_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_mul_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_mul_assign(&self, ct: &mut Ciphertext, scalar: u8) {
let acc = self.generate_msg_lookup_table(|x| scalar as u64 * x, self.message_modulus);
self.apply_lookup_table_assign(ct, &acc);
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// The result is returned in a _new_ ciphertext.
///
/// The operation is modulo the the precision bits to the power of two.
///
/// 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 multiplication:
/// let ct_res = sks.unchecked_scalar_mul(&ct, 3);
///
/// 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 multiplication:
/// let ct_res = sks.unchecked_scalar_mul(&ct, 3);
///
/// let clear = cks.decrypt(&ct_res);
/// assert_eq!(3, clear);
/// ```
pub fn unchecked_scalar_mul(&self, ct: &Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_result = ct.clone();
self.unchecked_scalar_mul_assign(&mut ct_result, scalar);
ct_result
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// The result it stored in the given ciphertext.
///
/// The operation is modulo the the precision bits to the power of two.
///
/// 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 multiplication:
/// sks.unchecked_scalar_mul_assign(&mut ct, 3);
///
/// 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 multiplication:
/// sks.unchecked_scalar_mul_assign(&mut ct, 3);
///
/// let clear = cks.decrypt(&ct);
/// assert_eq!(3, clear);
/// ```
pub fn unchecked_scalar_mul_assign(&self, ct: &mut Ciphertext, scalar: u8) {
unchecked_scalar_mul_assign(ct, scalar);
}
/// Multiply one ciphertext with a scalar in the case the carry space cannot fit the product
/// applying the message space modulus in the process.
///
/// This is a bootstrapped 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 clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
///
/// // Compute homomorphically a multiplication
/// sks.unchecked_scalar_mul_lsb_small_carry_modulus_assign(&mut ct_1, clear_2 as u8);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_1);
/// assert_eq!(clear_2 * clear_1, res);
///
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_PBS_KS);
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
///
/// // Compute homomorphically a multiplication
/// sks.unchecked_scalar_mul_lsb_small_carry_modulus_assign(&mut ct_1, clear_2 as u8);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_1);
/// assert_eq!(clear_2 * clear_1, res);
/// ```
pub fn unchecked_scalar_mul_lsb_small_carry_modulus_assign(
&self,
ct: &mut Ciphertext,
scalar: u8,
) {
// Modulus of the msg in the msg bits
let modulus = ct.message_modulus.0 as u64;
let acc_mul = self.generate_lookup_table(|x| (x.wrapping_mul(scalar as u64)) % modulus);
self.apply_lookup_table_assign(ct, &acc_mul);
}
/// Verify if the ciphertext can be multiplied by a scalar.
///
/// # 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 multiplication can be computed:
/// sks.is_scalar_mul_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 multiplication can be computed:
/// sks.is_scalar_mul_possible(ct.noise_degree(), 3).unwrap();
/// ```
pub fn is_scalar_mul_possible(
&self,
ct: CiphertextNoiseDegree,
scalar: u8,
) -> Result<(), CheckError> {
//scalar * ct.counter
let final_degree = scalar as usize * ct.degree.get();
self.max_degree.validate(Degree::new(final_degree))?;
self.max_noise_level
.validate(ct.noise_level * scalar as usize)?;
Ok(())
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// If the operation is possible, the result is returned in a _new_ ciphertext.
/// Otherwise a [CheckError] is returned.
///
/// The operation is modulo the precision bits to the power of two.
///
///
/// # 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 multiplication:
/// let ct_res = sks.checked_scalar_mul(&ct, 3).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 scalar multiplication:
/// let ct_res = sks.checked_scalar_mul(&ct, 3).unwrap();
///
/// let clear_res = cks.decrypt(&ct_res);
/// assert_eq!(clear_res, 3);
/// ```
pub fn checked_scalar_mul(
&self,
ct: &Ciphertext,
scalar: u8,
) -> Result<Ciphertext, CheckError> {
//If the ciphertext cannot be multiplied without exceeding the degree max
self.is_scalar_mul_possible(ct.noise_degree(), scalar)?;
let ct_result = self.unchecked_scalar_mul(ct, scalar);
Ok(ct_result)
}
/// Compute homomorphically a multiplication of a ciphertext by 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 .
///
/// The operation is modulo the precision bits to the power of two.
///
/// # 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 multiplication:
/// sks.checked_scalar_mul_assign(&mut ct, 3).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 multiplication:
/// sks.checked_scalar_mul_assign(&mut ct, 3).unwrap();
///
/// let clear_res = cks.decrypt(&ct);
/// assert_eq!(clear_res, 3);
/// ```
pub fn checked_scalar_mul_assign(
&self,
ct: &mut Ciphertext,
scalar: u8,
) -> Result<(), CheckError> {
self.is_scalar_mul_possible(ct.noise_degree(), scalar)?;
self.unchecked_scalar_mul_assign(ct, scalar);
Ok(())
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// This checks that the multiplication 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 = 3_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// let ct_res = sks.smart_scalar_mul(&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!(3, 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_mul(&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!(3, clear % modulus);
/// ```
#[allow(clippy::needless_pass_by_ref_mut)]
pub fn smart_scalar_mul(&self, ct: &mut Ciphertext, scalar: u8) -> Ciphertext {
let mut ct_result = ct.clone();
self.smart_scalar_mul_assign(&mut ct_result, scalar);
ct_result
}
/// Compute homomorphically a multiplication of a ciphertext by a scalar.
///
/// This checks that the multiplication 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 = 3_u8;
///
/// // Encrypt a message
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.smart_scalar_mul_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// 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(msg);
///
/// // Compute homomorphically a scalar multiplication:
/// sks.smart_scalar_mul_assign(&mut ct, scalar);
///
/// // Our result is what we expect
/// let clear = cks.decrypt(&ct);
/// assert_eq!(3, clear);
/// ```
pub fn smart_scalar_mul_assign(&self, ct: &mut Ciphertext, scalar: u8) {
// Direct scalar computation is possible
if self
.is_scalar_mul_possible(ct.noise_degree(), scalar)
.is_ok()
{
self.unchecked_scalar_mul_assign(ct, scalar);
ct.degree = Degree::new(ct.degree.get() * scalar as usize);
}
// If the ciphertext cannot be multiplied without exceeding the degree max
else {
self.evaluate_msg_univariate_function_assign(ct, |x| scalar as u64 * x);
ct.degree = Degree::new(self.message_modulus.0 - 1);
}
}
}
pub(crate) fn unchecked_scalar_mul_assign(ct: &mut Ciphertext, scalar: u8) {
ct.set_noise_level(ct.noise_level() * scalar as usize);
ct.degree = Degree::new(ct.degree.get() * scalar as usize);
match scalar {
0 => {
trivially_encrypt_lwe_ciphertext(&mut ct.ct, Plaintext(0));
}
1 => {
// Multiplication by one is the identidy
}
scalar => {
let scalar = u64::from(scalar);
let cleartext_scalar = Cleartext(scalar);
lwe_ciphertext_cleartext_mul_assign(&mut ct.ct, cleartext_scalar);
}
}
}