int fence_cipher(unsigned char* data, int data_length, int n)

{

unsigned char* ret;

int i, j, k = 0;

if (data_length

return 2;

}

if ( n = data_length ) {

return 1;

}

ret = (unsigned char*)calloc(1, data_length + 1);

if (ret == NULL) {

return 3;

}

for (i = 0; i

{

for (j = 0; j * (n + 1)

{

if (j * (n + 1) - i >= 0) {

ret[k++] = data[j * (n + 1) - i];

}

if (i != 0 && i != n - 1 && j * (n + 1) + i

ret[k++] = data[j * (n + 1) + i];

}

}

}

ret[k] = "\0";

strncpy((char *)data, (char *)ret, data_length);

free(ret);

return 0;

}