blob: a3d70b9c96e3e4d2237ea7738a72558e51741e4c (
plain)
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
|
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This package implements functions that are often useful in cryptographic
// code but require careful thought to use correctly.
package subtle
// ConstantTimeCompare returns 1 iff the two equal length slices, x
// and y, have equal contents. The time taken is a function of the length of
// the slices and is independent of the contents.
func ConstantTimeCompare(x, y []byte) int {
var v byte
for i := 0; i < len(x); i++ {
v |= x[i] ^ y[i]
}
return ConstantTimeByteEq(v, 0)
}
// ConstantTimeSelect returns x if v is 1 and y if v is 0.
// Its behavior is undefined if v takes any other value.
func ConstantTimeSelect(v, x, y int) int { return ^(v-1)&x | (v-1)&y }
// ConstantTimeByteEq returns 1 if x == y and 0 otherwise.
func ConstantTimeByteEq(x, y uint8) int {
z := ^(x ^ y)
z &= z >> 4
z &= z >> 2
z &= z >> 1
return int(z)
}
// ConstantTimeEq returns 1 if x == y and 0 otherwise.
func ConstantTimeEq(x, y int32) int {
z := ^(x ^ y)
z &= z >> 16
z &= z >> 8
z &= z >> 4
z &= z >> 2
z &= z >> 1
return int(z & 1)
}
// ConstantTimeCopy copies the contents of y into x iff v == 1. If v == 0, x is left unchanged.
// Its behavior is undefined if v takes any other value.
func ConstantTimeCopy(v int, x, y []byte) {
xmask := byte(v - 1)
ymask := byte(^(v - 1))
for i := 0; i < len(x); i++ {
x[i] = x[i]&xmask | y[i]&ymask
}
return
}
|
