CODEWITHSUNDEEP
c#c++c#-4.0
bvg
bvg

Reputation: 156

How to convert C++ unsigned char* to C#?

I have a method in C++ created for AES 256 Encryption which works:

void AES_Encrypt(unsigned char* message, unsigned char* expandedKey)
{
      unsigned char numOfRounds = 13;
      unsigned char* state = new unsigned char[16];

      AddRoundKey(state, expandedKey);
      for (int i = 0; i < numOfRounds; i++)
      {
          //bla bla
          AddRoundKey(state, expandedKey + (16 * (i + 1)));
      }

      // bla bla
      AddRoundKey(state, expandedKey + 224);
}

and

void AddRoundKey(unsigned char *state, unsigned char* roundKey)
{
    for (int i = 0; i < 16; i++)
        state[i] = state[i] ^ roundKey[i];
}

but when I translate it into C#:

private void AddRoundKey(byte[] state, byte[] roundKey)
{
    for (int i = 0; i < 16; i++)
        state[i] = (byte)(state[i] ^ roundKey[i]);
}

I get errors on the exact translated function:

AddRoundKey(state, expandedKey + (16 * (i + 1)));
AddRoundKey(state, expandedKey + 224);

How could I translate void AddRoundKey(unsigned char *state, unsigned char* roundKey) correctly in this case?

Upvotes: 1

Views: 234

Answers (1)

Stefan W.
Stefan W.

Reputation: 352

Simplest way will be passing the offset:

void AddRoundKey(byte[] state, byte[] roundKey, int offset)
    {
        for (int i = 0; i < 16; i++)
            state[i] = (byte)(state[i] ^ roundKey[i + offset]);
    }

then you call it:

        AddRoundKey(state, expandedKey, (16 * (i + 1)));
        ...
        AddRoundKey(state, expandedKey, 244);

Other

You can use unsafe keyword (notice to enable unsafe in your project settings)

unsafe void AddRoundKey(byte* state, byte* roundKey)
    {
        for (int i = 0; i < 16; i++)
            state[i] = (byte)(state[i] ^ roundKey[i]);
    }

then use fixed when you call it:

fixed (byte* state_pointer = state, expandedKey_pointer = expandedKey)
        {
            AddRoundKey(state_pointer, expandedKey_pointer + 244);
        }

when state and expandedKey is byte[].

Upvotes: 1

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