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Encryption is the process of encoding data or a message so that it cannot be understood by anyone other than its intended recipient. In computer processing, encryption means that data can be stored and transmitted securely by the sending computer to the receiving computer. The data or message is encrypted using an encryption algorithm. The opposite of encryption is decryption.

An encryption key is a piece of information - usually random characters - used by the software algorithm to encrypt data or a message into a form which is unreadable (encryption) and allow the data or message to be made readable again (decryption).

Unencrypted messages are referred to as plaintext messages. Encrypted messages are known as ciphertext.

There are many uses of encryption. These include:

• Encrypting data stored on a laptop hard disk. This is important as a laptop might contain sensitive information and could be easily stolen. If the hard disk is encrypted, the information will be unreadable unless the thief also has the key. In this situation it is usually a username and password.
• When sending sensitive information, such as passwords or credit card details, over the internet. When a website uses the HTTPS protocol (see the networks study guide for further details) the information being transferred is encrypted. This means that if the connection is intercepted, the information will be unreadable.
• Encrypting a document, such as a spreadsheet, using software tools, before sending it to a colleague via the internet, for security purposes.
• Encrypting satellite TV transmissions to prevent users who do not subscribe from watching TV shows.