1 // Licensed to the .NET Foundation under one or more agreements.
2 // The .NET Foundation licenses this file to you under the MIT license.
3 // See the LICENSE file in the project root for more information.
4 
5 using System;
6 using System.Diagnostics;
7 using System.Security.Cryptography;
8 
9 namespace Internal.Cryptography
10 {
11     internal static class Helpers
12     {
CloneByteArray(this byte[] src)13         public static byte[] CloneByteArray(this byte[] src)
14         {
15             if (src == null)
16             {
17                 return null;
18             }
19 
20             return (byte[])(src.Clone());
21         }
22 
CloneKeySizesArray(this KeySizes[] src)23         public static KeySizes[] CloneKeySizesArray(this KeySizes[] src)
24         {
25             return (KeySizes[])(src.Clone());
26         }
27 
UsesIv(this CipherMode cipherMode)28         public static bool UsesIv(this CipherMode cipherMode)
29         {
30             return cipherMode != CipherMode.ECB;
31         }
32 
GetCipherIv(this CipherMode cipherMode, byte[] iv)33         public static byte[] GetCipherIv(this CipherMode cipherMode, byte[] iv)
34         {
35             if (cipherMode.UsesIv())
36             {
37                 if (iv == null)
38                 {
39                     throw new CryptographicException(SR.Cryptography_MissingIV);
40                 }
41 
42                 return iv;
43             }
44 
45             return null;
46         }
47 
IsLegalSize(this int size, KeySizes[] legalSizes)48         public static bool IsLegalSize(this int size, KeySizes[] legalSizes)
49         {
50             for (int i = 0; i < legalSizes.Length; i++)
51             {
52                 KeySizes currentSizes = legalSizes[i];
53 
54                 // If a cipher has only one valid key size, MinSize == MaxSize and SkipSize will be 0
55                 if (currentSizes.SkipSize == 0)
56                 {
57                     if (currentSizes.MinSize == size)
58                         return true;
59                 }
60                 else if (size >= currentSizes.MinSize && size <= currentSizes.MaxSize)
61                 {
62                     // If the number is in range, check to see if it's a legal increment above MinSize
63                     int delta = size - currentSizes.MinSize;
64 
65                     // While it would be unusual to see KeySizes { 10, 20, 5 } and { 11, 14, 1 }, it could happen.
66                     // So don't return false just because this one doesn't match.
67                     if (delta % currentSizes.SkipSize == 0)
68                     {
69                         return true;
70                     }
71                 }
72             }
73             return false;
74         }
75 
GenerateRandom(int count)76         public static byte[] GenerateRandom(int count)
77         {
78             byte[] buffer = new byte[count];
79             using (RandomNumberGenerator rng = RandomNumberGenerator.Create())
80             {
81                 rng.GetBytes(buffer);
82             }
83             return buffer;
84         }
85 
86         // encodes the integer i into a 4-byte array, in big endian.
WriteInt(uint i, byte[] arr, int offset)87         public static void WriteInt(uint i, byte[] arr, int offset)
88         {
89             unchecked
90             {
91                 Debug.Assert(arr != null);
92                 Debug.Assert(arr.Length >= offset + sizeof(uint));
93 
94                 arr[offset] = (byte)(i >> 24);
95                 arr[offset + 1] = (byte)(i >> 16);
96                 arr[offset + 2] = (byte)(i >> 8);
97                 arr[offset + 3] = (byte)i;
98             }
99         }
100 
FixupKeyParity(this byte[] key)101         public static byte[] FixupKeyParity(this byte[] key)
102         {
103             byte[] oddParityKey = new byte[key.Length];
104             for (int index = 0; index < key.Length; index++)
105             {
106                 // Get the bits we are interested in
107                 oddParityKey[index] = (byte)(key[index] & 0xfe);
108 
109                 // Get the parity of the sum of the previous bits
110                 byte tmp1 = (byte)((oddParityKey[index] & 0xF) ^ (oddParityKey[index] >> 4));
111                 byte tmp2 = (byte)((tmp1 & 0x3) ^ (tmp1 >> 2));
112                 byte sumBitsMod2 = (byte)((tmp2 & 0x1) ^ (tmp2 >> 1));
113 
114                 // We need to set the last bit in oddParityKey[index] to the negation
115                 // of the last bit in sumBitsMod2
116                 if (sumBitsMod2 == 0)
117                     oddParityKey[index] |= 1;
118             }
119             return oddParityKey;
120         }
121 
ConvertIntToByteArray(uint value, byte[] dest)122         internal static void ConvertIntToByteArray(uint value, byte[] dest)
123         {
124             Debug.Assert(dest != null);
125             Debug.Assert(dest.Length == 4);
126             dest[0] = (byte)((value & 0xFF000000) >> 24);
127             dest[1] = (byte)((value & 0xFF0000) >> 16);
128             dest[2] = (byte)((value & 0xFF00) >> 8);
129             dest[3] = (byte)(value & 0xFF);
130         }
131     }
132 }
133 
134