Cryptography, once the almost exclusive preserve of governments, is increasingly seen as an enabling technology for the information society. These allow it to be used for the protection of privacy, the conduct of electronic commerce and the security of intellectual property on the information highway. Encryption is the transformation of data into a form unreadable by anyone without a secret decryption key. Its purpose is to ensure privacy by keeping the information hidden from anyone for whom it is not intended, even those who can see the encrypted data. For example, one may wish to encrypt files on a hard disk to prevent an intruder from reading them.
Encryption also allows secure communication over an otherwise insecure channel like the Internet.
This method is known as secret-key cryptography. The main problem is getting the sender and receiver to agree on the secret key without anyone else finding out. If they are in separate physical locations, they must trust a courier, or a phone system, or some other transmission system to not disclose the secret key being communicated. Anyone who overhears or intercepts the key in transit can later read all messages encrypted using that key. Secret-key cryptography often has difficulty providing secure key management.