Symmetric Key Encryption

What is it?

Symmetric key encryption uses one private key in order to encrypt and decrypt information.

This means that both the encryptor and the decryptor need to have the key, but this key can’t be made publicly available. In other words, the recipient of the encrypted information must already have a copy of the correct key to decrypt it.

Despite being an older technique that asymmetric encryption, symmetric encryption is still widely used, as it is:

• faster to perform (requires fewer CPU cycles in order to complete)
• smaller network utilisation as less data is produced (no need to include key blocks with transmissions)

Where is it used?

Generally, anywhere where large amounts of data need encryption. Some examples include:

• Encrypting the contents of a database – this means that should a database fall into the wrong hands, or the contents of the database get leaked, the information is not viewable. It may be that the database management system itself looks after the key, or it may be that the application using that data holds the key. Either way, no exchanging of keys is required for this to work.
• Encrypting computer drives – again, as with the example above, this aims to ensure that if the hard drive is removed from a computer or laptop, its contents will be unreadable by third parties. The computer itself stores the key securely, and is therefore the only device able to decrypt and access the drive’s contents.