1. The Advanced Encryption Standard Part 1: Overview
CSCI 5857: Encoding and Encryption

2. Outline AES goals and history AES data structures
Overall AES round structure

3. AES History 1997: NIST calls for proposals for DES replacement
56-bit DES key not computationally secure
Triple DES very slow
DES S-Boxes poorly understood
1999: Several algorithms chosen as finalists
Rijndael (selected)
Twofish, Serpent, etc. (still used by some systems)
2001: Rijndael published by NIST as Advanced Encryption Standard

4. Goals of AES Security Cost
Minimum key size: 128 bits (computationally secure now)
Expandable to 192 or 256 bits (will still be computationally secure in future)
Block size: 128 bits (more possible mappings)
Designed for resistance to differential and linear cryptanalysis
Cost
Structure optimized for efficiency

5. AES Bytes and Words
Blocks represented as arrays of smaller groups of bits
Byte: 8 bits
Word: 32 bits (4 bytes in word)

6. AES States Each word (each 4 bytes) corresponds to column in state
Used to add confustion

7. Hexadecimal AES States
Example: 17 17
Note that a byte can be represented by a 2-digit hexadecimal (base 16) number

8. AES Structure

9. AES Round Structure SubBytes: Each byte transformed by an S-Box
ShiftRows: Permutation to swap bytes around
MixColumns: Matrix multiplication to permute bits within bytes
AddRoundKey: XOR result with current round key
Notes:
Extra AddRoundKey before first round
No MixColumns in last round

10. What’s Next Let me know if you have any questions
Continue on to the next lecture on AES: Mathematical Backgorund