How to use a set of numbers as the Key for RCA Encryption - string

Question

i would like to know how can i use a set of numbers as a KEY for the rc4 encryption.
According to the internet and wiki the KEY is actually a string of letters but the bytes are used . But in my program i need to use a 6 digit number as a KEY. Should i covert it to a string or how.
Key Sheudling Algorithm is indicated below.
void ksa(u_char *State, u_char *key) {
int byte, i, keylen, j=0;
keylen = (int) strlen((char *) key);
for(i=0; i<256; i++) {
j = (j + State[i] + key[i%keylen]) % 256;
swap(&State[i], &State[j]);
}
How can i modify the code or should i just convert the numbers to string.

Answer 1

Strings and numbers are both bytes. Here is a working RC4 code that accepts a key of unsigned chars:
#include<stdio.h>
#include<string.h>
#define SIZE 256
unsigned char SBox[SIZE];
int i;
int j;
void initRC4(unsigned char Key[]);
unsigned char getByte(void);
void initRC4(unsigned char Key[])
{
unsigned char tmp;
unsigned char KBox[SIZE];
for(i=0;i<SIZE;i++)
SBox[i]=i;
for(i=0;i<SIZE;i++)
KBox[i]=Key[i % strnlen(Key,SIZE)];
for(j=0,i=0;i<SIZE;i++)
{
j=(j+SBox[i]+KBox[i]) % SIZE;
tmp=SBox[i];
SBox[i]=SBox[j];
SBox[j]=tmp;
}
}
unsigned char getByte(void)
{
unsigned char tmp;
i=(i+1)%SIZE;
j=(j+SBox[i])%SIZE;
tmp=SBox[i];
SBox[i]=SBox[j];
SBox[j]=tmp;
return SBox[(SBox[i]+SBox[j])%SIZE];
}
First, you initialize the RC4 stream:
initRC4(key);
Then you do:
getByte()
...which always returns 1 byte from the RC4 stream you've set up.
One thing to remember though - a letter in string is not always equal to 1 byte. Same goes for the integers and number symbols in strings. Really, you must read an introduction to computer programming before you mess with ciphers.
Here is a demonstration of how bytes differ in strings in integers:
#include <string>
int main(int argc, char **argv) {
const int n=67898;
const std::string str = "67898";
const int arrayLength = sizeof(int);
const int stringArrayLength = str.size();
unsigned char *bytePtr=(unsigned char*)&n;
printf("Bytes for integer: ");
for(int i=0;i<arrayLength;i++)
{
printf("%X ", bytePtr[i]);
}
printf("\n");
printf("Bytes for string: ");
for(int i=0;i<stringArrayLength;i++)
{
printf("%X ", str.at(i));
}
printf("\n");
return 0;
}
Output:
Bytes for integer: 3A 9 1 0
Bytes for string: 36 37 38 39 38
There will usually be a terminating byte at the end of a string, so you could add +1 byte to string size.