Implement the RC4 stream cipher in C++. User should be able to enter any key tha
ID: 3914811 • Letter: I
Question
Implement the RC4 stream cipher in C++. User should be able to enter any key that is 5 bytes to 32 bytes long. Be sure to discard the first 3072 bytes of the pseudo random numbers. THE KEY OR THE INPUT TEXT MUST NOT BE HARD CODED IN THE PROGRAM.
Test your program with the following plain text:
You should write TWO separate programs: encryption and decryption. The encryption program should input the plaintext file and output a cipher text in hex. The decryption program should input the cipher text file in hex and output the plaintext.
Explanation / Answer
//program
#define SWAP(a, b) ((a) ^= (b), (b) ^= (a), (a) ^= (b))
class CRC4
{
public:
CRC4 ()
{
memset(sbox,0,256);
memset(key,0,256);
}
virtual ~CRC4 ()
{
memset(sbox,0,256);
memset(key,0,256);
}
char *Encrypt(char *pszText,const char *pszKey)
{
f=0, g=0,n = 0;
ilen = (int)strlen(pszKey);
for (m = 0; m < 256; m++)
{
*(key + m)= *(pszKey + (m % ilen));
*(sbox + m) = m;
}
for (m=0; m < 256; m++)
{
n = (n + *(sbox+m) + *(key + m)) &0xff;
SWAP(*(sbox + m),*(sbox + n));
}
ilen = (int)strlen(pszText);
for (m = 0; m < ilen; m++)
{
f = (f + 1) &0xff;
g = (g + *(sbox + f)) &0xff;
SWAP(*(sbox+f),*(sbox + g));
k = *(sbox + ((*(sbox + f) + *(sbox + g)) &0xff ));
if(k == *(pszText + m))
encoded text;
k = 0;
*(pszText + m) ^= k;
}
return pszText;
}
char *Decrypt(char *pszText,const char *pszKey)
{
return Encrypt(pszText,pszKey) ;
}
private:
unsigned char sbox[256];
unsigned char key[256],k;
int m, n, f, g, ilen;
};
class CBase32
{
public:
CBase32(){}
char *Encrypt(const char * srcp, int len, char * dstp)
{
register int f = 0;
char *dst = dstp;
for (f = 0; f < len - 2; f += 3)
{
*dstp++ = *(base32_map + ((*(srcp+f)>>2)&0x3f));
*dstp++ = *(base32_map + ((*(srcp+f)<< 4)&0x30 | (
*(srcp+f+1)>>4)&0x0f ));
*dstp++ = *(base32_map + ((*(srcp+f+1)<<2)&0x3C | (
*(srcp+f+2)>>6)&0x03));
*dstp++ = *(base32_map + (*(srcp+f+2)&0x3f));
}
srcp += f;
len -= f;
if(len & 0x02 )
{
*dstp++ = *(base32_map + ((*srcp>>2)&0x3f));
*dstp++ = *(base32_map + ((*srcp<< 4)&0x30 | (
*(srcp+1)>>4)&0x0f ));
*dstp++ = *(base32_map + ((*(srcp+1)<<2)&0x3C) );
*dstp++ = '=';
}
else if(len & 0x01 )
{
*dstp++ = *(base32_map + ((*srcp>>2)&0x3f));
*dstp++ = *(base32_map + ((*srcp<< 4)&0x30));
*dstp++ = '=';
*dstp++ = '=';
}
*dstp = '';
return dst;
}
void *Decrypt(const char * srcp, int len, char * dstp)
{
register int f = 0;
void *dst = dstp;
while(f < len)
{
*dstp++ = (B32_offset[*(srcp+f)] <<2 |
B32_offset[*(srcp+f+1)] >>4);
*dstp++ = (B32_offset[*(srcp+f+1)]<<4 |
B32_offset[*(srcp+f+2)]>>2);
*dstp++ = (B32_offset[*(srcp+f+2)]<<6 |
B32_offset[*(srcp+f+3)] );
f
+= 4;
}
srcp += f;
if(*(srcp-2) == '=')
{
*(dstp--) = '';
*(dstp--) = '';
}
else if(*(srcp-1) == '=')
*(dstp--) = '';
*dstp = '';
return dst;
};
size_t B32_length(size_t len)
{
size_t npad = len%3;
size_t size = (npad > 0)? (len +3-npad ) : len;
return (size*8)/6;
}
size_t Ascii_length(size_t len)
{
return (len*6)/8;
}
};
#include "Base32_RC4.h"
void main()
{
char str[32] = "This is a test for RC4 cypher";
CRC4 rc4;
printf("Demo for RC4 ");
printf("Plain text: %s ",str);
rc4.Encrypt(str,"Key");
printf("Encoded string: %s ",str);
rc4.Decrypt(str,"Key");
printf("Decoded string: %s ",str);
strcpy(str, "This is a test for Base32 cypher");
CBase32 base32;
char *dst;
dst = (char*)malloc( base32.B32_length(strlen(str))+1);
if(dst == NULL)
return;
printf(" Demo for Base32 ");
printf("Plain text: %s ",str);
base32.Encrypt(str,strlen(str),dst);
printf("Encoded string: %s ",dst);
memset(str,0,sizeof(str));
base32.Decrypt(dst,strlen(dst),str);
printf("Decoded string: %s ",str);
free(dst);
getchar();
}