In Partial Fulfillment in Professional Ethics:

Encryption:

Encryption refers to algorithmic schemes that encode plain text into non-readable form or cyphertext, providing privacy. The receiver of the encrypted text uses a "key" to decrypt the message, returning it to its original plain text form. The key is the trigger mechanism to the algorithm.

Until the advent of the Internet, encryption was rarely used by the public, but was largely a military tool. Today, with online marketing, banking, healthcare and other services, even the average householder is aware of encryption.

Web browsers will encrypt text automatically when connected to a secure server, evidenced by an address beginning with https. The server decrypts the text upon its arrival, but as the information travels between computers, interception of the transmission will not be fruitful to anyone "listening in." They would only see unreadable gibberish.

There are many types of encryption and not all of it is reliable. The same computer power that yeilds strong encryption can be used to break weak encryption schemes. Initially, 64-bit encryption was thought to be quite strong, but today 128-bit encryption is the standard, and this will undoubtedly change again in the future.

Encryption can also be applied to an entire volume or drive. To use the drive, it is "mounted" using a special decryption key. In this state the drive can be used and read normally. When finished, the drive is dismounted and returns to an encrypted state, unreadable by interlopers, Trojan horses, spyware or snoops. Some people choose to keep financial programs or other sensitive data on encrypted drives.

Encryption schemes are categorized as being symmetric or asymmetric. Symmetric key algorithms such as Blowfish, AES and DES, work with a single, prearranged key that is shared between sender and receiver. This key both encrypts and decrypts text. In asymmetric encryption schemes, such as RSA and Diffie-Hellman, the scheme creates a "key pair" for the user: a public key and a private key. The public key can be published online for senders to use to encrypt text that will be sent to the owner of the public key. Once encrypted, the cyphertext cannot be decrypted except by the one who holds the private key of that key pair. This algorithm is based around the two keys working in conjunction with each other. Asymmetric encryption is considered one step more secure than symmetric encryption, because the decryption key can be kept private.

Source: http://www.wisegeek.com/what-is-encryption.htm