Question

I am working on the DES (Data Encryption Standard) algorithm in my Cryptography class, as a part of which I have to write a C code which includes a function to check the parity of a DES key.

How can I do this?

Answer 1

I would just do a Google search, and pick one of the first results that comes up.

Taken from the above link:

bool AdjustDESKeyParity(UCHAR* pucKey, int nKeyLen)
{
   int cPar;
   for(int i = 0; i < nKeyLen; i++)
   {
      cPar = 0;
      for(int j = 0; j < DES::BLOCKSIZE; j++)
      {
         if(pucKey[i] & (0×01 << j))
            cPar = !cPar;
      }
      if(!cPar)
         pucKey[i] ^= 0×01;
   }
   return true;
}

This isn’t pure C, but it should be easy enough to translate.