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
|
module subtle
// constant_time_byte_eq returns 1 when x == y.
pub fn constant_time_byte_eq(x byte, y byte) int {
return int((u32(x ^ y) - 1) >> 31)
}
// constant_time_eq returns 1 when x == y.
pub fn constant_time_eq(x int, y int) int {
return int((u64(u32(x ^ y)) - 1) >> 63)
}
// constant_time_select returns x when v == 1, and y when v == 0.
// it is undefined when v is any other value
pub fn constant_time_select(v int, x int, y int) int {
return (~(v - 1) & x) | ((v - 1) & y)
}
// constant_time_compare returns 1 when x and y have equal contents.
// The runtime of this function is proportional of the length of x and y.
// It is *NOT* dependent on their content.
pub fn constant_time_compare(x []byte, y []byte) int {
if x.len != y.len {
return 0
}
mut v := byte(0)
for i in 0 .. x.len {
v |= x[i] ^ y[i]
}
return constant_time_byte_eq(v, 0)
}
// constant_time_copy copies the contents of y into x, when v == 1.
// When v == 0, x is left unchanged. this function is undefined, when
// v takes any other value
pub fn constant_time_copy(v int, mut x []byte, y []byte) {
if x.len != y.len {
panic('subtle: arrays have different lengths')
}
xmask := byte(v - 1)
ymask := byte(~(v - 1))
for i := 0; i < x.len; i++ {
x[i] = x[i] & xmask | y[i] & ymask
}
}
// constant_time_less_or_eq returns 1 if x <= y, and 0 otherwise.
// it is undefined when x or y are negative, or > (2^32 - 1)
pub fn constant_time_less_or_eq(x int, y int) int {
x32 := int(x)
y32 := int(y)
return int(((x32 - y32 - 1) >> 31) & 1)
}
|
