When Is an Encryption Algorithm Symmetrical & When Is It Asymmetrical?

Asymmetric encryption algorithms are more secure than their symmetric counterparts.

An encryption algorithm is a mathematical formula used to encode data so that it cannot be viewed or modified by anyone other than the intended recipient. An encryption algorithm is symmetrical if it uses the same encryption key -- a value that must be fed into the algorithm to decode an encrypted message -- for both encryption and decryption. An encryption algorithm is asymmetrical if it uses different keys for encryption and decryption.

Symmetric Encryption

Symmetric encryption algorithms work by dividing data into units, or blocks, and applying a secret key -- a number, a word or a string of random letters -- to each block to change its content in some way. This process may involve shifting each letter by a number of places in the alphabet, switching letters around or changing them into numbers, but as long as the sender and recipient know the secret key they can encrypt or decrypt all messages that use it.

Asymmetric Encryption

Asymmetric encryption algorithms treat unencrypted text, known as plaintext, as if it were a huge number. They raise the number to the power of another huge number, divide it by a third huge number and convert the remainder back into text, known as ciphertext. Asymmetric encryption algorithms rely on two different, but related, encryption keys, known as public key and a private key. The public key is freely distributed to anyone who might want to send a message, while the private key is kept secret.

Security

One of the problems with symmetric encryption is the requirement to exchange, or share, a secret key over a large network or the Internet. The confidentiality of a message depends on the secrecy of the key, so anyone who knows it -- including intruders who may discover or intercept it -- can decrypt messages encrypted with it. Symmetric encryption algorithms are therefore inherently less secure than asymmetric encryption algorithms, in which the private key cannot be derived from the public key.

Performance

Asymmetric encryption algorithms are more complex and more secure than symmetric encryption algorithms, but they also require far more processing power to encrypt and decrypt messages. As a result, asymmetric encryption algorithms are correspondingly slower -- up to 1,000 times slower in some cases -- than their symmetric counterparts. Symmetric encryption algorithms are typically fast and are commonly used for conducting e-commerce, or business transactions over the Internet.

References

• PC World: How It Works: Encryption
• Microsoft: Description of Symmetric and Asymmetric Encryption
• The Privacy Commission: Symmetric and Asymmetric Cryptography