Once a message has been encrypted, it can be stored on nonsecure media or transmitted over a nonsecure network and still remain secret. Later, the message can be decrypted into its original form. This process is shown in the following illustration.
Data encryption and decryption is a simple process. When a message is encrypted, an encryption key is used. This is comparable to a key that is used to lock a padlock. To decrypt the message, a decryption key must be used. The encryption and decryption keys are often, but not always, the same key.
It is very important to keep the keys safe and transmit them securely to other users. This is discussed further in Encrypting and Decrypting Data. However, the challenge is to properly restrict access to the decryption key, because anyone who possesses it will be able to decrypt all messages that were encrypted with the corresponding encryption key.