Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Block Ciphers - Introduction to Cryptography - Lecture Slides, Slides of Network security

The major points in the database are given as: Block Ciphers, Twofish, Four Kinds of Importance, Protect Assets, Technology, Train People, Security, Enhance Security, Encrypting, Ciphertext Block

Typology: Slides

2012/2013

Uploaded on 04/22/2013

sathiamoorthy
sathiamoorthy 🇮🇳

4.4

(24)

106 documents

1 / 17

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
1
Block Ciphers
Docsity.com
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff

Partial preview of the text

Download Block Ciphers - Introduction to Cryptography - Lecture Slides and more Slides Network security in PDF only on Docsity!

1

Block Ciphers

2

Ciphers

  • Block cipher
  • DES
  • 3DES
  • AES
  • IDEA
  • Twofish

4

Block Cipher

  • Block cipher is an encryption function that works on fixed size blocks
  • Current block size is 128 bits
  • Encrypting a 128-bit plaintext block produces a 128-bit ciphertext block
  • The encryption key is also a series of bits, usually 128 or 256 bits
  • A secure block cipher is one that keeps the plaintext secret

5

Block Cipher

  • Trivial distinguisher involves creating all possible encryptions of 0 with all the keys in the range 1, 2, …, 2 32
  • A round is a collection of repetitions of a weak block cipher

7

DES

  • 64 bits are represented in 8 bytes. The rightmost bit in each byte is used as an odd parity bit. Since there are only 7 effective bits then, the encryption key strength is limited to 7 x 8 = 56 bits
  • Lucifer takes a 64-bit block and divides it into a left and right block of 32-bits each
  • Some operation is performed to permute the bits and then interchange the permuted 32-bit blocks. This is called round 1.

8

DES

  • Repeat this process for 16 rounds
  • Each round uses a 48-bit key chosen from the 56-bit key
  • Key for each round is different

10

DES

  • DES has complementation property
  • X’ denotes the complement of X where all the 0s of X are replaced by 1s and vice versa
  • E(K’,P’) = (E(K,P))’. Here E denotes encryption of plaintext P with key K. This is the complementation property.

11

DES

  • XOR has the property that if you XOR twice, then you get the original back: C = A xor B C xor B yields A back
  • E.g., Consider 10111010 xor 11001011 -------------- 01110001 xor 11001011 -------------- 10111010

13

Triple DES

  • 3DES was developed to address the key size problem
  • Modern computers have enough power to break the DES key in a short time (3 days or less)
  • With three keys, 3DES makes it very difficult to break the keys
  • NIST’s goal was to develop a strong encryption standard. NIST approved 3DES as an interim standard.

14

AES

  • Advanced Encryption Standard had two goals:
    • 128-bit or higher encryption
    • Usability with portable devices such as cell phones and PDAs
    • Developed through an international competition for proposals
    • Dutch scientists Joan Daemon and Vincent Rijmen developed the Rijndael (pronounced rain doll) cipher
    • Rijndael was adopted as the AES standard in 2001
    • AES provides 128, 192, or 256-bit encryption using blocks of size 128, 192, or 256-bits
    • All 9 combinations of key size and block size are valid

16

IDEA

  • International Data Encryption Algorithm is a 64-bit block cipher
  • Developed in 1991 by Lai and Massey in Switzerland
  • Uses 128-bit key
  • Has 8 and 1/2 rounds in the algorithm
  • Software is patented in U.S. but is free for non-commercial use

17

Twofish

  • Developed by Ferguson and Schneier
  • Twofish was a finalist for AES
  • Uses Feistel structure like DES
  • Provides 128-bit security
  • Uses 16 rounds
  • Twofish is more expensive to implement than Rijndael