11. Drawback of ECB
• Identical blocks of ciphertext.
• An eavesdropper notices that blocks 23 and
95 of the ciphertext are equal.
• If, in addition, he knows (or can guess) the
value of block 23 of plaintext, he can then
deduce the content of block 95 of the
plaintext
18. Counter Mode
• A b-bit counter is initialized to a random value.
This value is encrypted with the secret key.
• Encrypted value is XORed with the first block of
plaintext
• The counter is then incremented.
• the incremented value is encrypted and XORed
with the next block of plaintext to create the
ciphertext and so on.
21. DES
• Data Encryption Standard/Algorithm
• Adopted in 1977 by National Institute of
Standards and Technology (NIST)
• Plaintext 64 bit/Block
• Key 56 bit
36. Introduction
• Regular DES is not very secure and triple
DES is slow. The block size in both is 64 bits
• A more secure secret key algorithm with a
larger block size is desirable
• In 2001, Rijndael was selected by NIST from
among 5 finalists as the new standard
37. AES features
• Block size = 128 bits
• Key size = 128/192/256 bits
• No of rounds = 10, 12 or 14
• Does not have a Fiestal structure
38. AES Encryption
• Each round includes
– Byte substitution
– Row shift
– Column mixing
– Subkey Addition
49. Symmetric Key Cipher
• Single Shared Key is used for Encryption and
Decryption.
• Fast and Effective
• DES , AES , Salsa20
• Limitation
o Key Exchange
o Repetition of Key