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| /*
* rc4.c - written for readability
*
* http://blog.markloiseau.com/2012/07/rc4-tutorial/
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
typedef unsigned char u_char;
// Output level, from 0 to 3
#define OUTPUT 2
// Function prototypes
void initialize(u_char *State);
void swap(u_char *a, u_char *b);
void ksa(u_char *State, u_char *key);
u_char * prng(u_char *State, int msglength);
void rc4(u_char *key, u_char *input, u_char *output);
int main(int argc, char *argv[]) {
u_char key[256]; // The encryption/decryption key
u_char input[256]; // The input data
u_char output[256]; // The output
strncpy((char *) key, "Secret", 256);
strncpy((char *) input, "Attack at dawn", 256);
// encrypt
rc4(key, input, output);
#if OUTPUT >= 1
int i = 0;
printf("\n\n--- Encryption ---");
printf("\nOutput:\n");
for(i=0; i<strlen((char *) input); i++) {
if(output[i]<16)
printf("0%x ", output[i]);
else
printf("%x ", output[i]);
}
printf("\n");
#endif
// decrypt
rc4(key, output, input);
#if OUTPUT >= 1
printf("\n\n--- Decryption ---");
printf("\nOutput:\n");
printf("%s\n", input);
#endif
exit(0);
}
/*
* RC4 functions
*/
/* Initialize State[256] to the identity permutation. */
void initialize(u_char *State) {
int i;
for(i=0; i<256; i++) {
State[i] = i;
}
#if OUTPUT == 3
printf("Initialized State[]:\n");
for(i=0; i<16; i++)
printf(" 0%x ", State[i]);
printf("\n");
for(i=1; i<16; i++) {
for(j=0; j<16; j++)
printf(" %x ", State[16*i+j]);
printf("\n");
}
#endif
return;
}
/* Swap array elements i=State[i] and b=State[j]. */
void swap(u_char *i, u_char *j) {
u_char temp;
temp = *i;
*i = *j;
*j = temp;
}
/* Key scheduling algorithm. Swap array elements based on the key. */
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]);
}
#if OUTPUT >= 2
printf("Key scheduled State[]:\n");
for(i=0; i<16; i++) {
for(j=0; j<16; j++) {
byte = State[16*i+j];
if(byte<16)
printf(" 0%x ", byte);
else
printf(" %x ", byte);
}
printf("\n");
}
#endif
return;
}
/* Pseudo-random number generator: Generate the keystream. */
u_char * prng(u_char *State, int msglength) {
int i=0, j=0, k;
u_char *keystream;
keystream = (u_char *)malloc(sizeof(u_char)*msglength);
for(k=0; k<msglength; k++) {
i = (i+1) % 256;
j = (j+State[i]) % 256;
swap(&State[i], &State[j]);
keystream[k] = State[(State[i]+State[j]) % 256];
}
return keystream;
}
/* Encrypt or Decrypt */
void rc4(u_char *key, u_char *input, u_char *output) {
int i;
u_char State[256];
u_char *keystream;
initialize(State);
ksa(State, key);
keystream = prng(State, strlen((char *) input));
for(i=0; i<strlen((char *) input); i++)
output[i] = input[i] ^ keystream[i];
#if OUTPUT >= 1
printf("\n--- Key Generation ---\nKey: %s\n", key);
printf("Keystream:\n");
for(i=0; i<strlen((char *) input); i++) {
if(keystream[i]<16)
printf("0%x ", keystream[i]);
else
printf("%x ", keystream[i]);
}
#endif
return 0;
} |
