I ran this source code in VS 15 but there was no output shown. Need help with th
ID: 3915257 • Letter: I
Question
I ran this source code in VS 15 but there was no output shown. Need help with the output.
I'm trying to encrypt and decrpyt this text file.
Source code:
#include<iostream>
#include <stdio.h>
#include <stdint.h>
#include <assert.h>
typedef uint8_t byte;
typedef struct
{
byte i, j;
byte S[256];
} Rc4State;
void swap(byte *a, byte *b)
{
byte temp = *a;
*a = *b;
*b = temp;
}
/*Initialization & initial permutation
also initialize i&j counters in state for stream generation*/
void initState(const byte K[256], int keylen, Rc4State *state)
{
byte T[256];
assert(keylen >= 1 && keylen <= 256);
int i;
for (i = 0; i < 256; i++) {
state->S[i] = i;
T[i] = K[i % keylen];
}
//Initial permutation of S
byte *S = state->S;
int j = 0;
for (i = 0; i < 256; i++) {
j = (j + S[i] + T[i]) % 256;
swap(&S[i], &S[j]);
}
//Initialize counters in state
state->i = state->j = 0;
}
/*Encrypt/Decrypt text by XORing with next byte of keystream*/
byte crypt(byte text, Rc4State *state)
{
byte t, k;
byte *i = &(state->i), *j = &(state->j);
byte *S = state->S;
*i = (*i + 1) % 256;
*j = (*j + S[*i]) % 256;
swap(&S[*i], &S[*j]);
t = (S[*i] + S[*j]) % 256;
k = S[t];
return text ^ k;
}
static byte rc4CryptByte(Rc4State *state, byte plainText)
{
byte *S = state->S;
byte i = ++(state->i);
byte j = (state->j += S[i]);
swap(&S[i], &S[j]);
byte t = S[i] + S[j];
byte k = S[t];
return plainText ^ k;
}
void rc4Crypt(Rc4State *state, byte text[], size_t len)
{
for (size_t i = 0; i < len; i++)
{
text[i] = rc4CryptByte(state, text[i]);
}
system("pause");
}
int main() {
}
Explanation / Answer
The reason you are not getting any output is because your main() is empty [main method is the entry point of compliation].
Since you have never called your methods inside main(), none of them were called to perform the encryption/decryption and hence you never got any output.
To get the desired output, you would need to call your methods, namley, initState(), crypt(), rc4Crypt() inside main() method. After this, you will get the desired output if your code implementation is correct.