# Appendix A. Encryption Standards

## A.1. Synchronous Encryption

### A.1.1. Advanced Encryption Standard - AES

In cryptography, the Advanced Encryption Standard (AES) is an encryption standard adopted by the U.S. Government. The standard comprises three block ciphers, AES-128, AES-192 and AES-256, adopted from a larger collection originally published as Rijndael. Each AES cipher has a 128-bit block size, with key sizes of 128, 192 and 256 bits, respectively. The AES ciphers have been analyzed extensively and are now used worldwide, as was the case with its predecessor, the Data Encryption Standard (DES).

^{[5]}#### A.1.1.1. AES History

AES was announced by National Institute of Standards and Technology (NIST) as U.S. FIPS PUB 197 (FIPS 197) on November 26, 2001 after a 5-year standardization process. Fifteen competing designs were presented and evaluated before Rijndael was selected as the most suitable. It became effective as a standard May 26, 2002. It is available in many different encryption packages. AES is the first publicly accessible and open cipher approved by the NSA for top secret information.

### A.1.2. Data Encryption Standard - DES

The Data Encryption Standard (DES) is a block cipher (a form of shared secret encryption) that was selected by the National Bureau of Standards as an official Federal Information Processing Standard (FIPS) for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is based on a symmetric-key algorithm that uses a 56-bit key. The algorithm was initially controversial with classified design elements, a relatively short key length, and suspicions about a National Security Agency (NSA) backdoor. DES consequently came under intense academic scrutiny which motivated the modern understanding of block ciphers and their cryptanalysis.

^{[7]}#### A.1.2.1. DES History

DES is now considered to be insecure for many applications. This is chiefly due to the 56-bit key size being too small; in January, 1999, distributed.net and the Electronic Frontier Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes. There are also some analytical results which demonstrate theoretical weaknesses in the cipher, although they are unfeasible to mount in practice. The algorithm is believed to be practically secure in the form of Triple DES, although there are theoretical attacks. In recent years, the cipher has been superseded by the Advanced Encryption Standard (AES).

^{[8]}^{[5] }"Advanced Encryption Standard."

*Wikipedia.*14 November 2009 http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

^{[6] }"Advanced Encryption Standard."

*Wikipedia.*14 November 2009 http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

^{[7] }"Data Encryption Standard."

*Wikipedia.*14 November 2009 http://en.wikipedia.org/wiki/Data_Encryption_Standard

^{[8] }"Data Encryption Standard."

*Wikipedia.*14 November 2009 http://en.wikipedia.org/wiki/Data_Encryption_Standard

^{[9] }"Data Encryption Standard."

*Wikipedia.*14 November 2009 http://en.wikipedia.org/wiki/Data_Encryption_Standard