Thread: Help with my encryption program

Hey can someone help out here so it can encrypt and decrypt, i've been trying to figure it for a while and I can encrypt but I can decrypt, help would be appreciated. Thanks

CODE::

cout<<"Enter something you want to encrypt: "<<endl;
cin.get(user, 256);
cin.ignore(80, '\n');
string_length=strlen(user);

do
{
user[x];
l++; x++;
}

while(x!=string_length);

cout<<endl;
cout<<"Encrypted: "<<endl;
cout<<endl;
cout<<user<<endl;
cout<<endl;
cout<<"Press any key to continue"<<endl;
int wait= getch();

clrscr();

cout<<"Would you like to decrypt it? 1 = yes / 0 = no"<<endl;
cin >>user_choice;

if (user_choice==1)
{
x=0; l=33;
cout<<"Test"<<endl;
do
{
user[x]=l;
l--; x++;
}

while(x!=string_length);

do
{
user[x];
l++; x++;
}

I don't get it. How does that encrypt anything?

Code:

do { 
   user[x]; 
   l++; x++; 
}  while(x!=string_length);

This doesn't do anything to user[x] - sure it reads it, but that's all.

A most trivial encryption would be

Code:

do { 
   user[x]++; 
   x++; 
}  while(x!=string_length);

The decode for this would be

Code:

do { 
   user[x]--; 
   x++; 
}  while(x!=string_length);

THanks, that worked

Have two strings: a user plaintext string and a key string:

Code:

char user [31];   // 30 chars.
char key [31];

int userLength;
int keyLength;
int currentKeyByte = 0;

cout << "Enter string: ";
cin >> user;

cout << "Enter key: ";
cin >> key;

userLength = strlen (user);
keyLength = strlen (key);

for (i = 0; i < userLength; i++)
{
   user [i] ^= key [currentKeyByte];
   currentKeyByte++;

   currentKeyByte %= keyLength;
}

or something.

Salem:

do {
user[x]++;
x++;
} while(x!=string_length);


This works but how can I make it so it doesnt just increase the decimal of the ASCII by 1, I want to make it, for example, double and then divide or something to make it a complicated encryption.

Thanks

well
you can do

user[x] += 2 to add 2 but that is no very strong encryption, I suggest you use a key and 'mix up' the bits (^=) like samGwilliam already said.

is the %= operator equal to a=a%b

> This works but how can I make it so it doesnt just increase the decimal of the ASCII by 1

In general, you have
&nbsp;&nbsp;&nbsp;&nbsp;user[x] = encrypt(user[x]);

You can make encrypt anything you want, the only restriction is that it is a reversible process (the reverse is decrypt).

So adding 1 has an obvious inverse which is subtract 1

The rest is down to your imagination, and creating a pair of functions called encrypt() and decrypt() which mirror one another

I made a file encryption program. The encrypt and decrypt functions are referenced by a pointer. The address of this is decided before the loop so as to avoid an if statement every iteration, just one outside it.