Implementation of Vernam Cipher in C

vernam_cipher.c

/*
The MIT License (MIT)

Copyright (c) 2014 Tanay PrabhuDesai

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef char* STRING;
void vernam_encrypt_decrypt(STRING *text, STRING key)
{
	int txt_len = strlen(*text);
	int key_len = strlen(key);
	int txt_counter, key_counter;
	for (txt_counter = 0, key_counter = 0; txt_counter < txt_len ; ++txt_counter, key_counter=(key_counter+1)%key_len)
		(*text)[txt_counter] ^= key[key_counter];
}

void flush_stdin()
{
	while(fgetc(stdin) != '\n');
}

void print_binary_for_ascii(STRING text)
{
	int txt_length = strlen(text);
	int txt_counter, byte_counter;
	char temp_char;
	for(txt_counter = 0 ; txt_counter < txt_length ; ++txt_counter)
	{
		for (byte_counter = 0,  temp_char = text[txt_counter]; byte_counter < 8 ; ++byte_counter, temp_char<<=1)
			if(temp_char&128)
				printf("1");
			else
				printf("0");
		printf(" ");
	}
}

void print_binary_for_ascii_repeat(STRING text, int txt_max)
{
	int txt_length = strlen(text);
	int txt_counter, byte_counter, txt_index;
	char temp_char;
	for(txt_counter = 0, txt_index = 0 ; txt_counter < txt_max ; ++txt_counter, txt_index=(txt_index+1)%txt_length)
	{
		for (byte_counter = 0,  temp_char = text[txt_counter]; byte_counter < 8 ; ++byte_counter, temp_char<<=1)
			if(temp_char&128)
				printf("1");
			else
				printf("0");
		printf(" ");
	}
}

int main(int argv,char** argc)
{
	int key_length;
	int txt_length;
	char *key;
	char *str;

	printf("Enter the length of the key: ");
	scanf("%d",&key_length);

	printf("Enter the key to be used for encryption: ");
	key = (char*)malloc((key_length+1)*sizeof(char));
	flush_stdin();
	fgets(key,key_length+1,stdin);

	printf("Enter the length of the text: ");
	scanf("%d",&txt_length);

	printf("Input the string you want to encrypt: ");
	flush_stdin();
	str = (char*)malloc((txt_length+1)*sizeof(char));
	fgets(str,txt_length+1,stdin);

	printf("\nPlaintext:");
	printf("\nBinary: ");
	print_binary_for_ascii(str);
	printf("\n");

	printf("\nKey:");
	printf("\nBinary: ");
	print_binary_for_ascii_repeat(str,txt_length);
	printf("\n");

	vernam_encrypt_decrypt(&str,key); //encrypt
	printf("\nAfter Encryption:");
	printf("\nBinary: ");
	print_binary_for_ascii(str);

	vernam_encrypt_decrypt(&str,key); //decrypt
	printf("\nAfter decrypting:");
	printf("\nBinary: ");
	print_binary_for_ascii(str);
	printf("\n");

	free(str);
	free(key);
	return 0;
}

SAMPLE OUTPUT:

Enter the length of the key: 2
Enter the key to be used for encryption: nh
Enter the length of the text: 5
Input the string you want to encrypt: hello

Plaintext:
Binary: 01101000 01100101 01101100 01101100 01101111 

Key:
Binary: 01101000 01100101 01101100 01101100 01101111 

After Encryption:
Binary: 00000110 00001101 00000010 00000100 00000001 
After decrypting:
Binary: 01101000 01100101 01101100 01101100 01101111