Slide 1

AES Proposal: Rijndael
Joan Daemen

Vincent Rijmen

“Rijndael is expected, for all key and block
lengths defined, to behave as good as can
be expected from a block cipher with the
given block and key lengths.”

Presented by

Jianning TANG


Slide 2

Outline









Introduction
Applications of Rijndael
Design Criteria
Rijndael Encryption
Resistance Against Known Attacks
Security goal
Conclusion
Question


Slide 3

Introduction
AES:
Advanced Encryption Standard published by NIST
Block Cipher:
An encrypting method in which each block of plain text is
converted into a block of cipher text of the same length

Rijndael:
An iterated block cipher with a variable block length and a
variable key length. The block length and the key length can be
independently specified to 128, 192 or 256 bits.


Slide 4

Applications of Rijndael
Rijndael cipher is designed to be implemented efficiently on a wide range of
processors and in dedicated hardware. i.e. Smart Card, ATM, HDTV, B-ISDN,

Voice and Satellite (encryption).

Rijndael can also be used in MAC algorithm, iterated hash function,
synchronous stream cipher, pseudo-random number generator,
self-synchronizing stream cipher.


Slide 5

Design Criteria
• Resistance against all known attacks;
• Speed and code compactness on a wide range of platforms;
• Design simplicity.


Slide 6

Rijndael Encryption
Pseudo code of Rijndael encryption:
Rijndael(State,CipherKey)
{
KeyExpansion(CipherKey,ExpandedKey) ;
AddRoundKey(State,roundKey[0]);
For( i=1 ; iFinalRound(State,roundKey[Nr]);// return State;
}

Block Length(bits)

Nr
Key Length(bits) 1 28
1 92
2 56

Nr: number of rounds

1 28
10
12

1 92
12
12

2 56
14
14

14

14

14


Slide 7

Resistance Against Known
Attacks
Attack:
If the computational time of a cryptanalysis method(to find the key) is
less than the computational time of an exhausted key search, the method
is said to be an effective attack.

Plain Text--Cipher Text Pairs:
Known to cryptanalyst.

Keys:
NOT known to cryptanalyst


Slide 8

List of known cryptanalysis methods:
 Symmetry properties and weak keys of the DES type
 Differential cryptanalysis
 Linear cryptanalysis
 Truncated differentials

 The Square attack
 Interpolation attacks
 Related-key attacks

No attack has yet been found to be effective
against Rijndael.


Slide 9

Security Goal
1.
K-security:
All possible attack strategies for Rijndael have the same expected work
factor and storage requirements as for the majority of possible block
ciphers with the same dimensions.

2.
Hermetic:
It does not have weaknesses that are not present for the majority of
block ciphers with the same block and key length.
Or:
its internal structure cannot be exploited in any application.
Rijndael is expected to achieve its security goal


Slide 10

Conclusion
In security aspect:
“Rijndael is expected, for all key and block lengths defined,
to behave as good as can be expected from a block cipher

with the given block and key lengths.”


Slide 11

Question
If a block cipher is k-security, do you think it is secure enough?