RC4

/*
	By Sirus Shahini
	~cyn
	[email protected]
*/

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

unsigned char                               s[256];
unsigned char                               t[256];


void swap(unsigned char *p1, unsigned char *p2){
	unsigned char t = *p1;
	*p1 = *p2;
	*p2 = t;
}

void rc4_init(unsigned char *key,int key_len){
	int	i,j=0;

	//Initial values of both vectors
	for (i=0;i<256;i++){
		s[i] = i;
		t[i] = key[i%key_len];
	}
	//Initial permutation
	for (i=0;i<256;i++){
		j = (j + s[i] + t[i])%256;
		swap(&s[i],&s[j]);
	}
}

void rc4(unsigned char  *key,int key_len,char *buff,int len){
	int i=0;
	unsigned long t1,t2;
	unsigned char val;
	unsigned char out;
	t1=0;t2=0;
	rc4_init(key,key_len);

	//process one byte at a time
	for (i=0;i<len;i++){
		t1 = (t1 + 1)%256;
		t2 = (t2 + s[t1])%256;
		swap(&s[t1],&s[t2]);
		val = (s[t1] + s[t2])%256;
		out = *buff ^ val;
		*buff=out;
		buff++;
	}
}

int main(int argc,char ** argv){
	char message[1000];
	int message_len ;
	int i;
	FILE *f_random = fopen("/dev/urandom","r");
	unsigned char key[11];

	if (!f_random){
		printf("Can't open urandom\n");
		return -1;
	}
	strcpy(message,"Find the treasure 3 meters away from that tall tree where the kid passes by!");
	message_len = strlen(message);
	fread(key,1,10,f_random);
	fclose(f_random);

	for (i=0;i<10;i++){
		key[i] = (char)((key[i]/256.0*(rand()%26))+65);
	}
	key[10]=0;
	printf("> Generated sample key: \033[96m%s\033[0m\n",key);
	printf("> Secret text: \033[1;94m%s\033[0m\n",message);
	printf("> Encryted message: \033[1;94m");
	rc4(key,10,message,message_len);
	//print HEX encoding of the encrypted message
	for (i=0;i<message_len;i++){
		printf("%02X",(unsigned char)message[i]);
	}
	printf("\n\033[0m> Decryted RC4 data with the same key: ");
	rc4(key,10,message,message_len);
	printf("\033[1;92m%s\033[0m\n",message);

	return 0;
}

 

'''
    ARC4 or ARCFOUR Algorithm Class with stream generator. 
    Author: C.d.B.
    License: MIT 
    git https://github.com/Holthuizen/RC4-Python 
'''

class RC4: 
    def __init__(self,key):  
        '''unit tests'''  
        if key == "":
            raise ValueError("key can not be empyt")
        if not isinstance(key, str):
            raise TypeError("key must be of type String")  

        #generator
        self.keygenerator =  self.PRGA_YIELD( self.KSA(list(key.encode())))

    #returns state array S
    def KSA(self,key):
        s = list(range(0,256))#internal state, array [0 - 255] 
        j = 0
        for i in range(256):
            j = (j+s[i]+key[i%len(key)])% 256
            s[i],s[j] = s[j],s[i] #list swap
        return s
    #returns keystream generator K
    def PRGA_YIELD(self,S):
        i,j = 0,0
        while True:
            i = (i + 1) % 256
            j = (j + S[i]) % 256
            S[i], S[j] = S[j], S[i]  # swap
            K = S[(S[i] + S[j]) % 256]
            yield K


# Test vectors  https://en.wikipedia.org/wiki/RC4 :

#example: 
keygenerator = RC4("Key").keygenerator
for c in range(10):
    print(next(keygenerator),end=' ') #bytes decimal, format to hex for comparison with test vectors.