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A Stick Figure Guide to the Advanced Encryption Standard (AES)

Sep 22, 2009

(A play in 4 acts. Please feel free to exit along with the stage
character that best represents you. Take intermissions as you see
fit. Click on the stage if you have a hard time seeing it. If you get
bored, you can jump to the code. Most importantly, enjoy the show!)

Act 1: Once Upon a Time...

intro
sad
aes act 1 scene 03 cinderella
aes act 1 scene 04 started
aes act 1 scene 05 judge
aes act 1 scene 06 nbs decree
aes act 1 scene 07 lucifer
aes act 1 scene 08 anoint des
aes act 1 scene 09 des ruled
aes act 1 scene 10 des defeated
aes act 1 scene 11 triple des
aes act 1 scene 12 nist decree
aes act 1 scene 13 rallied
aes act 1 scene 14 rijndael
aes act 1 scene 15 vote
aes act 1 scene 16 won
aes act 1 scene 17 intel
aes act 1 scene 18 crypto question

Act 2: Crypto Basics

aes act 2 scene 01 three big ideas
aes act 2 scene 02 confusion
aes act 2 scene 03 diffusion
aes act 2 scene 04 key secrecy
aes act 2 scene 05 aes details question

Act 3: Details

aes act 3 scene 01 sign this
aes act 3 scene 02 agreement
aes act 3 scene 03 state matrix
aes act 3 scene 04 initial round
aes act 3 scene 05 xor tribute
aes act 3 scene 06 key expansion part 1
aes act 3 scene 07 key expansion part 2a
aes act 3 scene 08 key expansion part 2b
aes act 3 scene 09 key expansion part 3
aes act 3 scene 10 intermediate round start
aes act 3 scene 11 substitute bytes
aes act 3 scene 12 shift rows
aes act 3 scene 13 mix columns
aes act 3 scene 14 add round key
aes act 3 scene 15 final round
aes act 3 scene 16 more rounds the merrier
aes act 3 scene 17 tradeoffs
aes act 3 scene 18 security margin
aes act 3 scene 19 in pictures
aes act 3 scene 20 decrypting
aes act 3 scene 21 modes
aes act 3 scene 22 questions what really happens
aes act 3 scene 23 math

Act 4: Math!

aes act 4 scene 01 algebra class
aes act 4 scene 02 reviewing the basics
aes act 4 scene 03 algebra coefficients
aes act 4 scene 04 remember multiplication growth
aes act 4 scene 05 cant go bigger
aes act 4 scene 06 clock math
aes act 4 scene 07 clock math polynomials
aes act 4 scene 08 divide by mx
aes act 4 scene 09 logarithms
aes act 4 scene 10 using logarithms
aes act 4 scene 11 polynomial as byte
aes act 4 scene 12 byte operations
aes act 4 scene 13 byte inverses
aes act 4 scene 14 sbox math
aes act 4 scene 15 round constants
aes act 4 scene 16 mix columns math
aes act 4 scene 17 crib sheet
aes act 4 scene 18 got it now
aes act 4 scene 19 so much more
aes act 4 scene 20 gotta go
aes act 4 scene 21 the end

Epilogue

I created a heavily-commented AES/Rijndael implementation to go along
with this post and put it on GitHub. In keeping with the
Foot-Shooting Prevention Agreement, it shouldn't be used for
production code, but it should be helpful in seeing exactly where all
the numbers came from in this play. Several resources were useful in
creating this:

  * [DesignOfRi]The Design of Rijndael is the book on the subject,
    written by the Rijndael creators. It was helpful in understanding
    specifics, especially the math (although some parts were beyond
    me). It's also where I got the math notation and graphical
    representation in the left and right corners of the scenes
    describing the layers (SubBytes, ShiftRows, MixColumns, and
    AddRoundKey).
  * The FIPS-197 specification formally defines AES and provides a
    good overview.
  * The Puzzle Palace, especially chapter 9, was helpful while
    creating Act 1. For more on how the NSA modified DES, see this.
  * More on Intel's (and now AMD) inclusion of native AES
    instructions can be found here and in detail here. - Other
    helpful resources include Wikipedia, Sam Trenholme's AES math
    series, and this animation.

Please leave a comment if you notice something that can be better
explained.

Update #1: Several scenes were updated to fix some errors mentioned
in the comments.
Update #2: By request, I've created a slide show presentation of this
play in both PowerPoint and PDF formats. I've licensed them under the
Creative Commons Attribution License so that you can use them as you
see fit. If you're teaching a class, consider giving extra credit to
any student giving a worthy interpretive dance rendition in
accordance with the Foot-Shooting Prevention Agreement.

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