You can use this tool to encrypt and decrypt ascii text.
Possible uses might include: keeping passwords, homework, MSN conversations, secret government files(:p) etc confidential.
I have included the source code in the swf. You can copy it to the clipboard from within the application. Feel free to use it and experiment with it.
It works as follows:
The encryption algorithm takes plaintext and keys as input. The keys are really just a list of all the possible characters, randomly mixed.
First the encryption function will generate 2 random numbers. The sum of these numbers is the amount by which the characters of your text are shifted over the range of random characters in the keys, modified by various other factors to break some obvious patterns. The 2 numbers are then added to the end of the result, and the one on the left is swapped with a random character in the string, whose position is determined by the random value of the other number. The result is a random looking string of characters, of which only the final character is known to contain a value which points to the position of the second character. However, both are also swapped with key characters, so there's no way to determine their numerical value without having the key. The same process is repeated for each iteration.
I'm not an expert on the subject of cryptography. In fact, I'm not at all educated on the subject, so I can't tell how secure the algorithm is. Use at your own risk.