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 much more aware of it.
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 them are reliable. The same computer power that yields strong encryption can be used to break weak schemes. Initially, 64-bit encryption was thought to be quite strong, but today 128-bit is the standard, and this will undoubtedly change again in the future.
Though browsers automatically encrypt information when connected to a secure website, many people choose to use encryption in their email correspondence as well. This can easily be accomplished with programs that feature plug-ins or interfaces for popular email clients. The most longstanding of these is called PGP (Pretty Good Privacy), a humble name for very strong military-grade encryption program. PGP allows one to not only encrypt email messages, but personal files and folders as well.
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.
Strong encryption makes data private, but not necessarily secure. To be secure, the recipient of the data — often a server — must be positively identified as being the approved party. This is usually accomplished online using digital signatures or certificates.
As more people realize the open nature of the Internet, email and instant messaging, encryption will undoubtedly become more popular. Without it, information passed on the Internet is not only available for virtually anyone to snag and read, but is often stored for years on servers that can change hands or become compromised in any number of ways. For all of these reasons, it is a goal worth pursuing.