Encryption

Encryption

Introduction

This standard specifies the Rijndael algorithm, a symmetric block cipher that can process data blocks of 128 bits, using cipher keys with lengths of 128, 192, and 256 bits. Rijndael was designed to handle additional block sizes and key lengths, however they are not adopted in this standard.

Throughout the remainder of this standard, the algorithm specified herein will be referred to as “the AES algorithm.” The algorithm may be used with the three different key lengths indicated above, and therefore these different “flavors” may be referred to as “AES-128”, “AES-192”, and “AES-256”.

Background

What is Encryption?

Encryption is the process of transforming information from an unsecured form (”clear” or “plaintext”) into coded information (”ciphertext”), which cannot be easily read by outside parties. The transformation process is controlled by an algorithm and a key. The process must be reversible so that the intended recipient can return the information to its original, readable form, but reversing the process without the appropriate encryption information should be impossible. This means that details of the key must also be kept secret.
Encryption is generally regarded as the safest method of guarding against accidental or purposeful security breaches. The strength of the encryption method is often measured in terms of work factor - the amount of force that is required to ‘break’ the encryption. A strong system will take longer to break, although this can be reduced by applying greater force (the more effort that is put into the attack, the less time required to break the code).