Need Help with base64

pycraze dennis.varghese at wipro.com
Mon Jul 23 14:29:01 CEST 2007


Hi ,

  I am currently trying to implement base64 encoding and decoding
scheme in C . Python has a module , base64 , that will  do the
encoding and decoding with ease . I am aware of OpenSSL having support
for base64 encoding and decoding , but i will have to now implement
both in C without using the openssl libraries .

    I was able to download a code w.r.t. base 64 encoding and
decoding . I am attaching the code below .


void encodeblock( unsigned char cin[3], unsigned char cout[4], int
nlen )
{

    cout[0] = cb64[ cin[0] >> 2 ];
    cout[1] = cb64[ ((cin[0] & 0x03) << 4) | ((cin[1] & 0xf0) >> 4) ];
    cout[2] = (unsigned char) (nlen > 1 ? cb64[ ((cin[1] & 0x0f) << 2)
| ((cin[2] & 0xc0) >> 6) ] : '=');
    cout[3] = (unsigned char) (nlen > 2 ? cb64[ cin[2] & 0x3f ] :
'=');
}


void decodeblock( unsigned char cin[4], unsigned char cout[3] )
{
    cout[ 0 ] = (unsigned char ) (cin[0] << 2 | cin[1] >> 4);
    cout[ 1 ] = (unsigned char ) (cin[1] << 4 | cin[2] >> 2);
    cout[ 2 ] = (unsigned char ) (((cin[2] << 6) & 0xc0) | cin[3]);
}


int base641_decodestring(char* pcstr,int size,char** ppcdest)
{
      unsigned char cin[4] = {""};
  unsigned char cout[3] = {""};
      unsigned char  cv = 0;
      int ni = 0;
  int nlen = 0;
      char* cptr = pcstr;
      *ppcdest = malloc(sizeof(char)*160);
      if (!*ppcdest)
        {
            return 1;
        }
      memset(*ppcdest,0,sizeof(char)*160);

  char* pcstring = malloc( sizeof(char) * SIZE);
    if (!pcstring)
      {
          aps_log("APS_log.txt","\nbae64.c:base64encode:malloc failed
\n");
          return 1;
      }
  memset(pcstring,'\0',SIZE);

        for( nlen = 0, ni = 0; ni < 4; ni++ )
  {
            cv = 0;
            while(  cv == 0 )
      {
                cv = (unsigned char) *cptr;
                cv = (unsigned char) ((cv < 43 || cv > 122) ? 0 :
cd64[ cv - 43 ]);
                if( cv )
    {
                    cv = (unsigned char) ((cv == '$') ? 0 : cv - 61);
                }
            }
            if( cptr++ )
      {
                nlen++;
                if( cv )
    {
                    cin[ ni ] = (unsigned char) (cv - 1);
                }
            }
            else
      {
                cin[ni] = 0;
            }
        }
        if( nlen )
  {
            decodeblock( cin, cout );

        }
  memcpy(*ppcdest,cout,160);
  return 0;
}/*end of base64_decode */

char* base64_encode(char* pcstr)
{
  unsigned char cin[3] = {""};
  unsigned char cout[4] = {""};
  int ni = 0;
  int nlen = 0;
  int flag = 1;
  char* cptr = pcstr;
  char* pcstring = malloc( sizeof(char) * SIZE);
    if (!pcstring)
      {
          aps_log("APS_log.txt","\nbae64.c:base64encode:malloc failed
\n");
          return (void*)0;
      }
  memset(pcstring,'\0',SIZE);
  while( flag )
  {
    for( ni = 0; ni < 3; ni++ )
    {
      cin[ni] = (unsigned char)*cptr;
      if( *++cptr != '\0' )
        nlen++;
      else
      {
        cin[ni] = 0;
              flag = 0;
        break;
      }
    }
    encodeblock(cin, cout,nlen);
    strcat(pcstring,cout);
  }

  return pcstring;

}/* end of base64_encode */


          But this code gives different hex values as compared to the
python base64.encodestring and base64.decodestring respectively .

         I need some help on this matter . I need some pointers on
where is the mistake for the above file .




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