Encryption is used to make sure that only authorized parties can access the information. As soon as information leaves a defined security domain, make sure the information is encoded in a cryptographic way. Encryption itself does not prevent interference but denies the information to be read by unauthorized people. Encryption helps protect sensitive data if physical security measures fail.
The plaintext information is encrypted using an encryption algorithm, which often uses a cipher to generate an encryption key used to encrypt the plaintext information. In principle it is possible to decrypt information which has been encrypted without possessing the encryption key, but for a well-designed encryption scheme, a tremendous amount of computational resources and expertise is required, where an authorized person can easily decrypt the information with the key provided by the originator.