XOR Encryption in C

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
//#include <conio.h> Need in Windows

char* encryption(char* str, char* key)
{
    int i = 0, j = 0;
    char* crypted = (char*) malloc(sizeof(str));
    if(strlen(key) > strlen(str))
    {
        printf("\nThe key cannot be larger than the string itself.");
        return NULL;
    }
    else
    {
        while(str[i] != '\0')
        {
            for(j = 0; j < strlen(key); j++)
            {
                if(j == (strlen(str)))
                    continue;
                else
                {
                    crypted[i] = str[i] ^ key[j];
                    i++;
                }
            }
        }
    }
    return crypted;
}


int main()
{
    char str[50], key[50];
    int i = 0;
    char* strptr;
    //clrscr(); Need this in Windows
    printf("Enter the string to be encrypted -: ");
    gets(str);
    printf("\nEnter the key to be used -: ");
    gets(key);
    printf("\nString in hex -: ");
    for(i = 0; str[i] != '\0'; i++)
        printf("%x", str[i]);
    strptr = encryption(str, key);
    if(strptr == NULL)
    {
        printf("\nEncryption failed.\n");
        //getch(); Need this in Windows
        exit(1);
    }
    printf("\nThe encrypted string in hexadecimal is -: ");
    for(i = 0; strptr[i] != '\0'; i++)
        printf("%x", strptr[i]);
    strptr = encryption(strptr, key);
    printf("\nDecrypting -: ");
    for(i = 0; strptr[i] != '\0'; i++)
        printf("%c", strptr[i]);
    printf("\n");
    //getch(); Need this in Windows
    return 0;
}