Everything within the circle of encryption requires your private key. You and only you have it, remember? You didn't give it to your partner for safekeeping, the nanny for emergencies, you kept it safe and stored it away where only you can access it. If you followed that simple, easy step, then welcome to the circle of encryption:

How does the text get encrypted? By taking the PLAIN TEXT, combining that with the private KEY, and creating what is called a BLOCK CIPHER. You now have an encrypted CIPHER TEXT:

And, of course, we apply the reverse to decrypt the encrypted text. We have to have the private key in order to do this. Remember, given the private key, anyone can decipher the data from encrypted data and vice versa. Now, if you are dealing with just plain strings, I'd be worried. But we are dealing with huge chunks of structured data, which makes it a nearly insurmountable task to crack your encryption.

There are two rules for a block cipher to be considered valid:

• We must be able to derive the plain text from the cipher key and vice versa given a key
• The function must be efficiently computable