blob: 4dfef479f437c8b1c8fc00901dfbe6bc15742dc9 (
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
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
|
using System.Diagnostics;
namespace Hazel.Crypto
{
public static class Const
{
/// <summary>
/// Compare two bytes for equality.
///
/// This takes care to always use a constant amount of time to prevent
/// leaking information through side-channel attacks.
///
/// This is aceived by collapsing the xor bits down into a single bit.
///
/// Ported from:
/// https://github.com/mendsley/tiny/blob/master/include/tiny/crypto/constant.h
/// </summary>
/// <returns>
/// Returns `1` is the two bytes or equivalent. Otherwise, returns `0`
/// </returns>
public static byte ConstantCompareByte(byte a, byte b)
{
byte result = (byte)(~(a ^ b));
// collapse bits down to the LSB
result &= (byte)(result >> 4);
result &= (byte)(result >> 2);
result &= (byte)(result >> 1);
return result;
}
/// <summary>
/// Compare two equal length spans for equality.
///
/// This takes care to always use a constant amount of time to prevent
/// leaking information through side-channel attacks.
///
/// Ported from:
/// https://github.com/mendsley/tiny/blob/master/include/tiny/crypto/constant.h
/// </summary>
/// <returns>
/// Returns `1` if the spans are equivalent. Others, returns `0`.
/// </returns>
public static byte ConstantCompareSpans(ByteSpan a, ByteSpan b)
{
Debug.Assert(a.Length == b.Length);
byte value = 0;
for (int ii = 0, nn = a.Length; ii != nn; ++ii)
{
value |= (byte)(a[ii] ^ b[ii]);
}
return ConstantCompareByte(value, 0);
}
/// <summary>
/// Compare a span against an all zero span
///
/// This takes care to always use a constant amount of time to prevent
/// leaking information through side-channel attacks.
///
/// Ported from:
/// https://github.com/mendsley/tiny/blob/master/include/tiny/crypto/constant.h
/// </summary>
/// <returns>
/// Returns `1` if the spans is all zeros. Others, returns `0`.
/// </returns>
public static byte ConstantCompareZeroSpan(ByteSpan a)
{
byte value = 0;
for (int ii = 0, nn = a.Length; ii != nn; ++ii)
{
value |= (byte)(a[ii] ^ 0);
}
return ConstantCompareByte(value, 0);
}
}
}
|
