AES (ADVANCED ENCRYPTION STANDARD)－好人勿用™

AES aka Rijndael加密法!!!
而... Rijndael的發音近於"Rhine doll" (萊茵河娃娃)~~~

AES經過五年的甄選: (AES vs Serpent vs Twofish vs MARS vc RC6)

由NIST(美國國家標準與技術研究院)於2001年11月26日發佈!
@ FIPS PUB 197(聯邦資料處理標準),並在2002年5月26日成為有效的標準!!!

AES Crib Sheet

(

這張手繪圖堪稱AES的精隨~ 可以幫助記憶與理解...)

Cipher detail
Designers	Vincent Rijmen, Joan Daemen
First published	1998
Derived from	Square
Successors	Anubis, Grand Cru
Certification	AES winner, CRYPTREC, NESSIE, NSA
Key sizes	128, 192 or 256 bits
Block sizes	128 bits
Structure	Substitution-permutation network
Rounds	10, 12 or 14 (depending on key size)

雖然... Symmetric Encryption概念簡單到爆!!!
而... AES就是基於Symmetric Encryption概念所設計來的演算法!!!

始終使用同一把金鑰來加解密

Let's Practice with Secret Key Encryption

然而... AES其實作一點都不簡單!!!
@ 取代(substitution)/置換(transposition)/相乘(Product)通通都得運用上!

Recap~ 密碼學上的幾個重要Idea:

Big Idea #1: Confusion(混亂性) (把你拷糊塗... 讓你猜不透...)

Big Idea #2: Diffusion(擴張性) (牽一髮而動全身的概念)

Big Idea #3: Secrecy Only in the Key!!!

就是因為Big Idea #3
Combo™必須借用谷歌大神 + Wiki百科來理解AES的運作原理~

How Does AES Work?

蹲馬步 @ AES演算法四大基本步驟:

1.) AddRoundKey: 基本上就是互斥或運算 (⊕)

AES ❤ XOR

2.) SubBytes: S-Box查表

► S-Box (Substitution-Box)

(左) S-Box Lookup Table (右) Inv S-Box Lookup Table

3.) ShiftRows: 乾坤大挪移

AES_ShiftRowTab[] = { 0,5,10,15,4, 9,14,3,8,13,2,7,12,1,6,11 };

4.) MixColumns: 合而為一

▩ a'(x)=a(x)⊗c(x)
a'_0,c= ({02}•a_0,c) ⊕ ({03}•a_1,c) ⊕ a_2,c⊕ a_3,c
a'_1,c = a_0,c ⊕ ({02}•a_1,c) ⊕ ({03}•a_2,c) ⊕ a _3,c
a'_2,c = a_0,c ⊕ a_1,c⊕ ({02}•a_2,c) ⊕ ({03}•a_3,c)
a'_3,c= ({03}•a_0,c) ⊕ a_1,c⊕ a_2,c⊕ ({02}•a_3,c)

(

其中ShiftRows&MixColumns兩步驟為AES密碼系統提供了Diffusion(擴散性)!!!)

The Laws of Cryptography: AES Key Expansion

http://www.cs.utsa.edu/~wagner/laws/AESkeys.html

AES Key Expansion = Rijndael Key Schedule

Flash Video Describing the AES key schedule:
http://www.formaestudio.com/rijndaelinspector/archivos/Rijndael_Animation_v4_eng.swf

(A) Encryption Process @ Page 4
(B) Key Schedule @ Page 14

@ Youtube

@ AES Encryption 1: Intro and Outline

Encryption Process:

Flash Video Describing the AES key schedule @ Page 4

Key Expansion:

Flash Video Describing the AES key schedule @ Page 14

11, 13, 15 rounds for 128, 192, 256 bits keys
- First Round
- Main Regular Rounds (9, 11, 13)
- Final Round (10^th, 12^th, 14^th)

AES-128 = Expansion of the given Cipher key into 11 partial keys
                                        (Initial round + 9 main rounds + final round)
AES-192 = Expansion of the given Cipher key into 13 partial keys
                                        (Initial round + 11 main rounds + final round)
AES-256 = Expansion of the given Cipher key into 15 partial keys
                                        (Initial round + 13 main rounds + final round)

(⊕) xor with "Round Constant":

RCON[i]=[Rcon[i],00,00,00]

C

O

N [i] = [R c o n [i], 00, 00, 00]

; xi−1

x^{i - 1}

(for i from 0 to 255)

i

0

255

RCON [0] = 0x8d is not used in AES algorithm.
RCON [1] = 0x01, RCON [2] = 0x02, RCON [3] = 0x04, RCON [4] = 0x08, RCON [5] = 0x10,
RCON [6] = 0x20, RCON [7] = 0x40, RCON [8] = 0x80, RCON [9] = 0x1B, RCON [10] = 0x36,
RCON [11] = 0x6C, RCON [12] = 0xD8, RCON [13] = 0xAB, RCON [14] = 0x4D.

AES是一種標準1 AES是一種標準!! AES是一種標準!!!
因為是Standard! 所以Intel Inside就把"AES Inside" since Westmere

Intel® AES NI:

Intel® 進階加密標準新增指令 (Intel® AES NI) 是一組新的加密指令集，
改善了進階加密標準 (AES) 演算法，可加速 Intel® Xeon® 處理器產品與
Intel® Core™ 處理器產品中的資料加密。
1. 好的演算法，亦即「進階加密標準」(AES) @ Intel® AES NI
2. 好的金鑰，亦即優質的隨機數字 @ Intel® Digital Random Number Generator，Intel® DRNG)

Intel® Advanced Encryption Standard (Intel® AES) Instructions Set

AES Encryption & Decryption Flow:

AES Encryption Flow:

(0). KeyExpansion()
(1). Round #1
    1. AddRoundKey()
(2). Regular Rounds (9, 11, 13) depend on Keys used
    1. SubBytes()
    2. ShiftRows()
    3. MixColumns()
    4. AddRoundKey()
(3). Last Round
    1. SubBytes()
    2. ShiftRows()
    3. AddRoundKey()

AES Decryption Flow:

(0). KeyExpansion()
(1). Round #1
    1. AddRoundKey()
(2). Regular Rounds (9, 11, 13) depend on Keys used
    1. InvShiftRows()
    2. InvSubBytes()
    3. AddRoundKey()
    4. InvMixColumns()
(3). Last Round
    1. InvShiftRows()
    2. InvSubBytes()
    3. AddRoundKey()

1. Each round = 4 steps of SubBytes, ShiftRows, MixColumns, and AddRoundKey.
2. Last round has only 3 steps. No MixColumns.
3. Decryption is not the same as encryption (as in DES).
4. Decryption consists of inverse steps.

ComboStyle™AES網誌的最後...

比利時不只是有美味高檔的GADIVA巧克力...
還有迷人奧秘的Rhine doll @ AES (Advanced Encryption Standard)!!!