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Fix AES-CMAC for incomplete blocks

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This commit is contained in:
Alex Barney 2018-12-20 17:09:30 -06:00
parent d29f7b27a7
commit 10e62b5ee1
2 changed files with 72 additions and 14 deletions
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27
src/LibHac/Crypto.cs
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@ -344,11 +344,12 @@ namespace LibHac
return t; return t;
} }
// https://stackoverflow.com/questions/29163493/aes-cmac-calculation-c-sharp
public static void CalculateAesCmac(byte[] key, byte[] src, int srcIndex, byte[] dest, int destIndex, int length) public static void CalculateAesCmac(byte[] key, byte[] src, int srcIndex, byte[] dest, int destIndex, int length)
{ {
var l = new byte[16]; var l = new byte[16];
EncryptCbc(key, new byte[16], new byte[16], l, 0x10); EncryptCbc(key, new byte[16], new byte[16], l, 0x10);
byte[] paddedMessage = src;
int paddedLength = length;
byte[] firstSubkey = Rol(l); byte[] firstSubkey = Rol(l);
if ((l[0] & 0x80) == 0x80) if ((l[0] & 0x80) == 0x80)
@ -358,28 +359,26 @@ namespace LibHac
if ((firstSubkey[0] & 0x80) == 0x80) if ((firstSubkey[0] & 0x80) == 0x80)
secondSubkey[15] ^= 0x87; secondSubkey[15] ^= 0x87;
int paddingBytes = 16 - length % 16; if (length != 0 && length % 16 == 0)
var srcPadded = new byte[length + paddingBytes];
Array.Copy(src, srcIndex, srcPadded, 0, length);
if (paddingBytes > 0)
{ {
srcPadded[length] = 0x80;
for (int j = 0; j < firstSubkey.Length; j++) for (int j = 0; j < firstSubkey.Length; j++)
srcPadded[length - 16 + j] ^= firstSubkey[j]; src[length - 16 + j] ^= firstSubkey[j];
} }
else else
{ {
paddedLength += 16 - length % 16;
paddedMessage = new byte[paddedLength];
paddedMessage[length] = 0x80;
Array.Copy(src, srcIndex, paddedMessage, 0, length);
for (int j = 0; j < secondSubkey.Length; j++) for (int j = 0; j < secondSubkey.Length; j++)
srcPadded[length - 16 + j] ^= secondSubkey[j]; paddedMessage[paddedLength - 16 + j] ^= secondSubkey[j];
} }
var encResult = new byte[length]; var encResult = new byte[paddedMessage.Length];
EncryptCbc(key, new byte[16], srcPadded, encResult, length); EncryptCbc(key, new byte[16], paddedMessage, encResult, paddedLength);
Array.Copy(encResult, length - 0x10, dest, destIndex, 0x10); Array.Copy(encResult, paddedLength - 0x10, dest, destIndex, 0x10);
} }
private static byte[] Rol(byte[] b) private static byte[] Rol(byte[] b)

59
tests/LibHac.Tests/AesCmac.cs Normal file
View file

@ -0,0 +1,59 @@
using Xunit;
namespace LibHac.Tests
{
public class AesCmac
{
private static readonly byte[] CmacKey = "2b7e151628aed2a6abf7158809cf4f3c".ToBytes();
private static readonly TestData[] TestVectors =
{
new TestData
{
Key = CmacKey,
Message = "".ToBytes(),
Expected = "bb1d6929e95937287fa37d129b756746".ToBytes()
},
new TestData
{
Key = CmacKey,
Message = "6bc1bee22e409f96e93d7e117393172a".ToBytes(),
Expected = "070a16b46b4d4144f79bdd9dd04a287c".ToBytes()
},
new TestData
{
Key = CmacKey,
Message = "6bc1bee22e409f96e93d7e117393172aae2d8a571e03ac9c9eb76fac45af8e5130c81c46a35ce411".ToBytes(),
Expected = "dfa66747de9ae63030ca32611497c827".ToBytes()
},
new TestData
{
Key = CmacKey,
Message = "6bc1bee22e409f96e93d7e117393172aae2d8a571e03ac9c9eb76fac45af8e5130c81c46a35ce411e5fbc1191a0a52eff69f2445df4f9b17ad2b417be66c3710".ToBytes(),
Expected = "51f0bebf7e3b9d92fc49741779363cfe".ToBytes()
}
};
[Theory]
[InlineData(0)]
[InlineData(1)]
[InlineData(2)]
[InlineData(3)]
public static void Encrypt(int index)
{
TestData data = TestVectors[index];
var actual = new byte[0x10];
Crypto.CalculateAesCmac(data.Key, data.Message, 0, actual, 0, data.Message.Length);
Assert.Equal(data.Expected, actual);
}
private struct TestData
{
public byte[] Key;
public byte[] Message;
public byte[] Expected;
}
}
}