Encryption and Decryption

The first term is encryption. It means the changing of the syntax of a message, making it unintelligible to the causal observer; it appears as a bunch of gibberish. This altered data is often called cipher text. Decryption is the opposite of encryption. It means changing the cipher text back to the original intelligible format – back to clear text.

Encryption and decryption are performed with one of the two methods, and often a combination of them. The first method is known by three names: private, symmetrical or conventional. Whatever the name used this method uses the same key for encryption and decryption. This key is a secret key, and it is shared between the sender and receiver of the message; that is, it is called a shared secret key. The sender uses the key to encrypt the clear text into cipher text, and the receiver uses the same key to decrypt the cipher text into clear text.

The second method is known by two names: public or asymmetric. This method uses two different keys; one is used for encryption and the other is used for decryption. One key is called the public key and the other is called a private key, and we will have much to say about these keys later.

Another term we need to introduce is the digital signature. It describes an authentication procedure to verify that the party who supposedly sent a message to another party is indeed the legitimate party. The best way to think of this operation is that it is like someone’s signature; it verifies that someone’s authenticity.

The final introductory term is called the hash, hash code, message digest or a hash function. This operation performs a calculation on a message of any length to produce a fixed-length value. When protected with encryption, it used to authenticate a sender of a message.