1. Triple DES

2. Algorithm Uses a block of size 64 bits.
Triple DES comprises of three DES keys, K1, K2 and K3, each of 56 bits. The encryption algorithm follows a EDE sequence:
C = E(K3, D(K2, E(K1, P)))
i.e., DES encrypt with K1, DES decrypt with K2, then DES encrypt with K3.

3. Triple DES

4. Applications
The electronic payment industry uses Triple DES and continues to develop and promulgate standards based upon it .
Microsoft OneNote and Microsoft Outlook 2007 use Triple DES to password protect user content.

5. Benefits of using 3DES
With 168-bit key length, it overcomes the vulnerability to brute-force attack of DEA.
Since it is based on the DES algorithm, it is very easy to modify existing software to use Triple DES.

6. Drawbacks
It has three times as many rounds as DES, is correspondingly slower.
Uses 64-bit block size. For reasons of both efficiency and security, a larger block size is desirable.
The National Institute of Standards and Technology (NIST) issued a call for proposals to develop the Advanced Encryption Standard (AES) as a replacement for DES

7. Advanced Encryption Standard

8. Proposed by Dr. Joan Daemen and Dr. Vincet Rijmen.
About AES
Symmetric block cipher, published in 2001 with a block length of 128-bits and a key length that can be 128, 192, 256 bits.
NIST selected Rijndael as the proposed AES algorithm after imposing an evaluation criteria which included security, computational efficiency, memory requirements, hardware and software suitability , and flexibility.
Proposed by Dr. Joan Daemen and Dr. Vincet Rijmen.

9. The AES Cipher
The input is a single 128 bit block, depicted as a square matrix of bytes.
This is copied into the State array which is modified at each stage of encryption and decryption.
After the final stage, the State is copied to an output matrix.
Input
State array
Output
in0
in4
in8
in12
S00
S01
S02
S03 o0 o4 o8
o12
in1
in5
in9
in13
S10
S11
S12
S13 o1 o5 o9
o13
in2
in6
in10
in14
S20
S21
S22
S23 o2 o6
o10
o14
in3
in7
in11
in15
S30
S31
S32
S33 o3 o7
o11
o15

10. The AES Cipher Key received as input array of 4 rows and Nk columns
Nk = 4,6, or 8, parameter which depends key size
Input key is expanded into an array of 44/52/60 words of 32 bits (4 bytes) each.
4 different words serve as a key for each round k0 k4 k8
k12 …… k1 k5 k9
k13 w0 w1 w2
w42
w43 k2 k6
k10
k14 k3 k7
k11
k15

11. The AES Cipher
Number of rounds, Nr, depends on key size and each round is a repetition of functions that perform a transformation over State array.
Consists of 4 main functions: one permutation and three substitutions
Substitute bytes, Shift rows, Mix columns, Add round key
There are 11 rounds and the key is expanded into an array of forty-four 32-bit words w[i]. Four distinct words are used for each round.

12. The AES Cipher
AddRoundKey() – A simple bitwise XOR of the current block with a portion of the expanded key.
MixColumns() – A substitution that alters each byte in a column as a function of all of the bytes in the column.
ShiftRows() –A simple permutation that is performed row by row.
SubBytes() – uses a table referred to as an S-box to perform a byte-by-byte substitution of State.

13. The AES Cipher plaintext key Add round key Substitute bytes
W[0,3]
Substitute bytes
Substitute bytes
Substitute bytes
Shift rows
Shift rows
Shift rows
Round 1
Round 9
Mix columns
Mix columns
Add round key
Add Round key
Add round key
Cipher text
W[4,7]
W[36,39]
W[40,43]
key

14. The AES Cipher Only Add round key makes use of the key.
Other three functions are reversible without knowledge of the key, hence add no security.
We can view the cipher as an alternating operations of XOR encryption followed by scrambling of the block, followed by XOR and so on.
This scheme is both efficient and highly secure.

15. The AES Inverse Cipher ciphertext Add round key Inv. Shift rows
Inv. Sub bytes
Inv. Sub bytes
Inv. Sub bytes
Round 1
Round 9
Add round key
Add round key
Add round key
Inv. Mix Columns
Inv. Mix columns
plaintext
W[36,39]
W[4,7]
W[0,3]
key

16. The AES Inverse Cipher
Decryption algorithm uses the expanded key in reverse order.
All functions are easily reversible and their inverse form is used in decryption
Decryption algorithm is not identical to the encryption algorithm. This is a consequence of the particular structure of AES.
Again, final round consists of only three stages. It is required to make the cipher reversible.

17. Applications
Encrypting File System in Windows XP SP1 and later Windows versions.
Disk encryption, File encryption.
IEEE i, an amendment to the original IEEE standard specifying security mechanisms for wireless networks, uses AES-128.

18. Thank you…