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Презентация на тему Cryptography and Network Security. Chapter 5. Fifth Edition by William Stallings

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2. Chapter 5 –Advanced Encryption Standard "It seems
3. AES Originsclear a replacement for DES was
4. The AES Cipher - Rijndael designed by
5. AES Encryption Process
6. AES Structuredata block of 4 columns of
7. AES Structure
8. Some Comments on AESan iterative rather than
9. Substitute Bytesa simple substitution of each byteuses
10. Substitute Bytes
11. Substitute Bytes Example
12. Shift Rowsa circular byte shift in each
13. Shift Rows
14. Mix Columnseach column is processed separatelyeach byte
15. Mix Columns
16. Mix Columns Example
17. AES Arithmeticuses arithmetic in the finite field
18. Mix Columnscan express each col as 4
19. Add Round KeyXOR state with 128-bits of
20. Add Round Key
21. AES Round
22. AES Key Expansiontakes 128-bit (16-byte) key and
23. AES Key Expansion
24. Key Expansion Rationaledesigned to resist known attacksdesign
25. AES Example Key Expansion
26. AES Example Encryption
27. AES Example Avalanche
28. AES DecryptionAES decryption is not identical to
29. AES Decryption
30. Implementation Aspectscan efficiently implement on 8-bit CPUbyte
31. Implementation Aspectscan efficiently implement on 32-bit CPUredefine
32. Скачать презентацию
33. Похожие презентации

Chapter 5 –Advanced Encryption Standard "It seems very simple.""It is very simple. But if you don't know what the key is it's virtually indecipherable."—Talking to Strange Men, Ruth Rendell

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Cryptography and Network Security. Chapter 5. Fifth Edition by William Stallings

Cryptography and Network Security Chapter 5Fifth Editionby William Stallings Lecture slides by Lawrie Brown

AES Originsclear a replacement for DES was neededhave theoretical attacks that can

The AES Cipher - Rijndael designed by Rijmen-Daemen in Belgium has 128/192/256

AES Structuredata block of 4 columns of 4 bytes is statekey is

Some Comments on AESan iterative rather than Feistel cipherkey expanded into array

Substitute Bytesa simple substitution of each byteuses one table of 16x16 bytes

Shift Rowsa circular byte shift in each each1st row is unchanged2nd row

Mix Columnseach column is processed separatelyeach byte is replaced by a value

AES Arithmeticuses arithmetic in the finite field GF(28)with irreducible polynomialm(x) = x8

Mix Columnscan express each col as 4 equationsto derive each new byte

Add Round KeyXOR state with 128-bits of the round keyagain processed by

AES Key Expansiontakes 128-bit (16-byte) key and expands into array of 44/52/60

Key Expansion Rationaledesigned to resist known attacksdesign criteria includedknowing part key insufficient

AES DecryptionAES decryption is not identical to encryption since steps done in

Implementation Aspectscan efficiently implement on 8-bit CPUbyte substitution works on bytes using

Implementation Aspectscan efficiently implement on 32-bit CPUredefine steps to use 32-bit wordscan

Summaryhave considered:the AES selection processthe details of Rijndael – the AES cipherlooked

Слайды презентации

Слайд 2 Chapter 5 –Advanced Encryption Standard
"It seems very simple."
"It

is very simple. But if you don't know what

the key is it's virtually indecipherable."
—Talking to Strange Men, Ruth Rendell

Слайд 3 AES Origins
clear a replacement for DES was needed
have

AES Originsclear a replacement for DES was neededhave theoretical attacks that

theoretical attacks that can break it
have demonstrated exhaustive key

search attacks
can use Triple-DES – but slow, has small blocks
US NIST issued call for ciphers in 1997
15 candidates accepted in Jun 98
5 were shortlisted in Aug-99
Rijndael was selected as the AES in Oct-2000
issued as FIPS PUB 197 standard in Nov-2001

Слайд 4 The AES Cipher - Rijndael
designed by Rijmen-Daemen

The AES Cipher - Rijndael designed by Rijmen-Daemen in Belgium has

in Belgium
has 128/192/256 bit keys, 128 bit data

an iterative rather than Feistel cipher
processes data as block of 4 columns of 4 bytes
operates on entire data block in every round
designed to have:
resistance against known attacks
speed and code compactness on many CPUs
design simplicity

Слайд 5 AES Encryption Process

Слайд 6 AES Structure
data block of 4 columns of 4

AES Structuredata block of 4 columns of 4 bytes is statekey

bytes is state
key is expanded to array of words
has

9/11/13 rounds in which state undergoes:
byte substitution (1 S-box used on every byte)
shift rows (permute bytes between groups/columns)
mix columns (subs using matrix multiply of groups)
add round key (XOR state with key material)
view as alternating XOR key & scramble data bytes
initial XOR key material & incomplete last round
with fast XOR & table lookup implementation

Слайд 7 AES Structure

Слайд 8 Some Comments on AES
an iterative rather than Feistel

Some Comments on AESan iterative rather than Feistel cipherkey expanded into

cipher
key expanded into array of 32-bit words
four words form

round key in each round
4 different stages are used as shown
has a simple structure
only AddRoundKey uses key
AddRoundKey a form of Vernam cipher
each stage is easily reversible
decryption uses keys in reverse order
decryption does recover plaintext
final round has only 3 stages

Слайд 9 Substitute Bytes
a simple substitution of each byte
uses one

Substitute Bytesa simple substitution of each byteuses one table of 16x16

table of 16x16 bytes containing a permutation of all

256 8-bit values
each byte of state is replaced by byte indexed by row (left 4-bits) & column (right 4-bits)
eg. byte {95} is replaced by byte in row 9 column 5
which has value {2A}
S-box constructed using defined transformation of values in GF(28)
designed to be resistant to all known attacks

Слайд 10 Substitute Bytes

Слайд 11 Substitute Bytes Example

Слайд 12 Shift Rows
a circular byte shift in each each
1st

Shift Rowsa circular byte shift in each each1st row is unchanged2nd

row is unchanged
2nd row does 1 byte circular shift

to left
3rd row does 2 byte circular shift to left
4th row does 3 byte circular shift to left
decrypt inverts using shifts to right
since state is processed by columns, this step permutes bytes between the columns

Слайд 13 Shift Rows

Слайд 14 Mix Columns
each column is processed separately
each byte is

Mix Columnseach column is processed separatelyeach byte is replaced by a

replaced by a value dependent on all 4 bytes

in the column
effectively a matrix multiplication in GF(28) using prime poly m(x) =x8+x4+x3+x+1

Слайд 15 Mix Columns

Слайд 16 Mix Columns Example

Слайд 17 AES Arithmetic
uses arithmetic in the finite field GF(28)
with

AES Arithmeticuses arithmetic in the finite field GF(28)with irreducible polynomialm(x) =

irreducible polynomial
m(x) = x8 + x4 + x3 +

x + 1
which is (100011011) or {11b}
e.g.
{02} • {87} mod {11b} = (1 0000 1110) mod {11b}
= (1 0000 1110) xor (1 0001 1011) = (0001 0101)

Слайд 18 Mix Columns
can express each col as 4 equations
to

Mix Columnscan express each col as 4 equationsto derive each new

derive each new byte in col
decryption requires use of

inverse matrix
with larger coefficients, hence a little harder
have an alternate characterisation
each column a 4-term polynomial
with coefficients in GF(28)
and polynomials multiplied modulo (x4+1)
coefficients based on linear code with maximal distance between codewords

Слайд 19 Add Round Key
XOR state with 128-bits of the

Add Round KeyXOR state with 128-bits of the round keyagain processed

round key
again processed by column (though effectively a series

of byte operations)
inverse for decryption identical
since XOR own inverse, with reversed keys
designed to be as simple as possible
a form of Vernam cipher on expanded key
requires other stages for complexity / security

Слайд 20 Add Round Key

Слайд 21 AES Round

Слайд 22 AES Key Expansion
takes 128-bit (16-byte) key and expands

AES Key Expansiontakes 128-bit (16-byte) key and expands into array of

into array of 44/52/60 32-bit words
start by copying key

into first 4 words
then loop creating words that depend on values in previous & 4 places back
in 3 of 4 cases just XOR these together
1st word in 4 has rotate + S-box + XOR round constant on previous, before XOR 4th back

Слайд 23 AES Key Expansion

Слайд 24 Key Expansion Rationale
designed to resist known attacks
design criteria

Key Expansion Rationaledesigned to resist known attacksdesign criteria includedknowing part key

included
knowing part key insufficient to find many more
invertible transformation
fast

on wide range of CPU’s
use round constants to break symmetry
diffuse key bits into round keys
enough non-linearity to hinder analysis
simplicity of description

Слайд 25 AES Example Key Expansion

Слайд 26 AES Example Encryption

Слайд 27 AES Example Avalanche

Слайд 28 AES Decryption
AES decryption is not identical to encryption

AES DecryptionAES decryption is not identical to encryption since steps done

since steps done in reverse
but can define an equivalent

inverse cipher with steps as for encryption
but using inverses of each step
with a different key schedule
works since result is unchanged when
swap byte substitution & shift rows
swap mix columns & add (tweaked) round key

Слайд 29 AES Decryption

Слайд 30 Implementation Aspects
can efficiently implement on 8-bit CPU
byte substitution

Implementation Aspectscan efficiently implement on 8-bit CPUbyte substitution works on bytes

works on bytes using a table of 256 entries
shift

rows is simple byte shift
add round key works on byte XOR’s
mix columns requires matrix multiply in GF(28) which works on byte values, can be simplified to use table lookups & byte XOR’s

Слайд 31 Implementation Aspects
can efficiently implement on 32-bit CPU
redefine steps

Implementation Aspectscan efficiently implement on 32-bit CPUredefine steps to use 32-bit

to use 32-bit words
can precompute 4 tables of 256-words
then

each column in each round can be computed using 4 table lookups + 4 XORs
at a cost of 4Kb to store tables
designers believe this very efficient implementation was a key factor in its selection as the AES cipher