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
use crate::server_key::CheckError;
use crate::server_key::CheckError::CarryFull;
use crate::{CrtCiphertext, ServerKey};
impl ServerKey {
/// Computes homomorphically a subtraction between a ciphertext and a scalar.
///
/// 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 = 7;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.unchecked_crt_scalar_sub_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_sub(&self, ct: &CrtCiphertext, scalar: u64) -> CrtCiphertext {
let mut result = ct.clone();
self.unchecked_crt_scalar_sub_assign(&mut result, scalar);
result
}
pub fn unchecked_crt_scalar_sub_assign(&self, ct: &mut CrtCiphertext, scalar: u64) {
//Put each decomposition into a new ciphertext
for (ct_i, mod_i) in ct.blocks.iter_mut().zip(ct.moduli.iter()) {
let neg_scalar = (mod_i - scalar % mod_i) % mod_i;
self.key
.unchecked_scalar_add_assign_crt(ct_i, neg_scalar as u8);
}
}
/// Verifies if the subtraction of a ciphertext by scalar can be computed.
///
/// # 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 = 7;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// let bit = sks.is_crt_scalar_sub_possible(&mut ctxt_1, clear_2);
///
/// // Decrypt
/// let res = cks.decrypt_crt(&ctxt_1);
/// assert_eq!(true, bit);
/// ```
pub fn is_crt_scalar_sub_possible(&self, ct: &CrtCiphertext, scalar: u64) -> bool {
for (ct_i, mod_i) in ct.blocks.iter().zip(ct.moduli.iter()) {
let neg_scalar = (mod_i - scalar % mod_i) % mod_i;
if !self.key.is_scalar_add_possible(ct_i, neg_scalar as u8) {
return false;
}
}
true
}
/// Computes homomorphically a subtraction of a ciphertext by a scalar.
///
/// 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 = 8;
/// let basis = vec![2, 3, 5];
///
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// let ct_res = sks.checked_crt_scalar_sub(&mut ctxt_1, clear_2)?;
///
/// // Decrypt:
/// let dec = cks.decrypt_crt(&ct_res);
/// assert_eq!((clear_1 - clear_2) % 30, dec);
/// # Ok(())
/// # }
/// ```
pub fn checked_crt_scalar_sub(
&self,
ct: &CrtCiphertext,
scalar: u64,
) -> Result<CrtCiphertext, CheckError> {
if self.is_crt_scalar_sub_possible(ct, scalar) {
Ok(self.unchecked_crt_scalar_sub(ct, scalar))
} else {
Err(CarryFull)
}
}
/// Computes homomorphically a subtraction of a ciphertext by a scalar.
///
/// 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 = 7;
/// let basis = vec![2, 3, 5];
///
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.checked_crt_scalar_sub_assign(&mut ctxt_1, clear_2)?;
///
/// // Decrypt:
/// let dec = cks.decrypt_crt(&ctxt_1);
/// assert_eq!((clear_1 - clear_2) % 30, dec);
/// # Ok(())
/// # }
/// ```
pub fn checked_crt_scalar_sub_assign(
&self,
ct: &mut CrtCiphertext,
scalar: u64,
) -> Result<(), CheckError> {
if self.is_crt_scalar_sub_possible(ct, scalar) {
self.unchecked_crt_scalar_sub_assign(ct, scalar);
Ok(())
} else {
Err(CarryFull)
}
}
/// Computes homomorphically a subtraction of a ciphertext by a 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 = 7;
/// let basis = vec![2, 3, 5];
/// // Encrypt two messages
/// let mut ctxt_1 = cks.encrypt_crt(clear_1, basis.clone());
///
/// sks.smart_crt_scalar_sub_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_sub(&self, ct: &mut CrtCiphertext, scalar: u64) -> CrtCiphertext {
if !self.is_crt_scalar_sub_possible(ct, scalar) {
self.full_extract(ct);
}
self.unchecked_crt_scalar_sub(ct, scalar)
}
pub fn smart_crt_scalar_sub_assign(&self, ct: &mut CrtCiphertext, scalar: u64) {
if !self.is_crt_scalar_sub_possible(ct, scalar) {
self.full_extract(ct);
}
self.unchecked_crt_scalar_sub_assign(ct, scalar);
}
}