Advanced Encryption Standard (AES)

TO KNOW:

• input\/output & req'd pptys of a secure block cipher

• 128- 192- 256-bit keys

• 128-bit blocks

• Not a Feistel Network: Galois Field Operations(GF(2^8)) to create PRP

  • addition = bitwise XOR, multiplication is another bitwise op
  • fast in software & hardware

Encryption\/Decryption

Galois Field Arithmetic

arithmetic operations of a var with a constant value creates a permutation

Addition

Multiplication

AES Round Function

AES Take Away Points

• For the purposes of this course it is less important that you understand the exact bits and bytes operations going on inside AES

• We’ll treat AES like a black box: you need to know inputs, outputs, and the required properties of a secure block cipher.

• It is more important that you understand how to use a block cipher in secure mode of operation.

• If you’re interested in more detail on how AES works, check out this great animation:

  http:\/\/www.formaestudio.com\/rijndaelinspector\/archivos\/Rijndael_Animation_v4_eng.swf

• If you want to understand more about its design and why it is the way it is, check out the FIPS specification:

  http:\/\/csrc.nist.gov\/publications\/fips\/fips197\/fips-197.pdf