Encryption_Decryption in C

Key Mismatch -

Matching Key -

Code -

...... Encryption Decryption in C (logic told in another post) ........

//___ Program for Encryption and Decryption in C ___

/* Program will read the message and an encryption key (which should be of only 3 digits) and based on that key

data will be encrypted and for decryption the program will again read a number and if it is same as that of the number being inputted the first time

original message can be obtained */

/* Encrypted message in not printed but you can edit the code to watch the encrypted message */


//____ Including Header Files ___


#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<stdlib.h> //__ Included for fflush(stdin) ___

char original_message[100];

int temp_variable = 0;

int encryption_message_key_scan();

int decryption_message_key_scan();

void message_encryption(char *original_message, int temp_key); //___ Function to encrypt the message ___

void message_decryption(char *original_message, int temp_key); //___ Function to decrypt the message ___

int main() //___ Main function from where the program execution starts ___
{
int temp = 0, counter = 0;



printf("\n\n\t\t__________ Encryption/Decryption in C _________\n\n");

printf("\n\n  1. Encryption will take place\n\n  2. Decryption will take place");

printf("\n\n\t Press Enter to Continue.....");

printf("\n\n________________________________________________________________________________");

while(getch() != 13)
{
}

fflush(stdin);

printf("\n\n  Encryption - ");

temp = encryption_message_key_scan();

message_encryption(original_message, temp++);

printf("\n\n________________________________________________________________________________");

printf("\n\n  Decryption - ");

temp = decryption_message_key_scan();

message_decryption(original_message, temp);

printf("\n\n  Your Message      -  ");

puts(original_message);

getch();

}

/* Function to scan the message and the encryption key based on which message will be encrypted */


int encryption_message_key_scan()
{

int encryption_key = 0;

printf("\n\n  Enter the Message -  ");

gets(original_message);

fflush(stdin);

printf("\n\n  Enter the Number  -  "); //___ Prompting the user to add the key ___

scanf("%d",&encryption_key); //__ Reading the three digit encryption key __

return encryption_key;

}

/* Function to scan the decryption key and the function return type is of integer i.e. it returns the decryption

key where the function is being called */

int decryption_message_key_scan()
{
int decryption_key = 0;

fflush(stdin);

printf("\n\n  Enter the Number  -  "); //___ Prompting the user to add the key ___

scanf("%d",&decryption_key); //__ Reading the three digit encryption key __

return decryption_key;

}

void message_encryption(char *original_message, int temp_key)
{
int encryption_key = 0, remainder = 0, first_digit = 0, last_digit = 0, string_length = 0, counter = 0;

char temp_character;

/* Counter in the while loop represents the place value

(0 place represents the ones/2 represents 100 place value) */

while(temp_key != 0)
{
remainder = temp_key % 10;

temp_key = temp_key / 10;


if(counter == 0 )
{
last_digit = remainder;
}
else if ( counter == 2)
{
first_digit = remainder;
}

counter++;
}

if (counter == 3) //___ if the number is of 3 digits then ___
{
string_length = 0; //___ String_length is used to count the number of characters in message ___

while(original_message[string_length] != '\0')

//___ Counting the number of characters in the message__

{
string_length++;
}



if (string_length%2 != 0) //__ According the algorithm if message length is odd, make it even ___
{
original_message[string_length] = 32;

original_message[string_length + 1] = '\0';

string_length++;
}

//___ Replacing the characters at the initial positions _____

temp_character = original_message[first_digit - 1];

original_message[first_digit - 1] = original_message[last_digit - 1];

original_message[last_digit - 1] = temp_character;

while((string_length >= first_digit * 2) && (string_length >= last_digit * 2))

/* The loop will continue till any of the condition is false i.e. if any of the digit is becomes greater

than message length loop will stop */
{
first_digit = first_digit * 2;

last_digit = last_digit * 2;

temp_character = original_message[first_digit - 1];

original_message[first_digit - 1] = original_message[last_digit - 1];

original_message[last_digit - 1] = temp_character;

}

counter = 0;

while(counter!= string_length) //__ Replacing the spaces will'@' __
{
if (original_message[counter] == ' ')
{
original_message[counter] = '@';
}
counter = counter + 1;
}
}
else
{
printf("\n\n\t\t __ 3 Digit Only __");
}
}

void message_decryption(char *original_message, int temp_key)
{
char temp_character;

int decryption_key = 0, string_length = 0, remainder = 0, counter = 0, previous_first = 0, previous_last = 0,last_digit = 0, first_digit = 0, original_first = 0, original_last = 0;

while(temp_key != 0)
{
remainder = temp_key % 10;

temp_key = temp_key / 10;

if (counter == 0 )
{
last_digit = remainder;
}
else if ( counter == 2)
{
first_digit = remainder;
}

counter++;
}

if (counter == 3)
{
string_length = 0;

while(original_message[string_length] != '\0')

//___ Counting the number of characters in the message__

{
string_length++;
}

original_first = first_digit;

original_last = last_digit;

counter = 0;

while(original_message[counter] != '\0') //__ Replacing '@' with space __
{
if (original_message[counter] == '@')
{
original_message[counter] = 32;
}
counter++;
}


while((first_digit <= string_length) && (last_digit <= string_length))
{
previous_first = first_digit;

previous_last = last_digit;

first_digit = first_digit * 2;

last_digit = last_digit * 2;
}

while((previous_first != original_first) && (previous_last != original_last))
{

temp_character = original_message[previous_first - 1];

original_message[previous_first - 1] = original_message[previous_last - 1];

original_message[previous_last - 1] = temp_character;

previous_first = previous_first/2;

previous_last = previous_last/2;

}

temp_character = original_message[previous_first - 1];

original_message[original_first - 1] = original_message[original_last - 1];

original_message[original_last - 1] = temp_character;

}
else
{
printf("\n\n\t\t __ 3 Digit only __");
}
}

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