Presentation is loading. Please wait.

Presentation is loading. Please wait.

Cryptography Basics and Symmetric Cryptography

Published byEliza Bianca Igrejas Silva Modified over 6 years ago

Similar presentations

Presentation on theme: "Cryptography Basics and Symmetric Cryptography"— Presentation transcript:

1 Cryptography Basics and Symmetric Cryptography
Prof. Ravi Sandhu Executive Director and Endowed Chair Lecture 2 © Ravi Sandhu World-Leading Research with Real-World Impact!

2 Basic Concepts World-Leading Research with Real-World Impact!
© Ravi Sandhu World-Leading Research with Real-World Impact!

3 Cryptographic Technology
SYMMETRIC KEY Secret Key Single Key Conventional ASYMMETRIC KEY Public Key Public-Private Key © Ravi Sandhu World-Leading Research with Real-World Impact! 3

4 Cryptographic Technology
Symmetric-key encryption Symmetric-key message authentication codes (MACs) Public-key encryption Public-key digital signatures Public-key key agreement Message digests (hash functions) Public-key certificates Challenge-response authentication © Ravi Sandhu World-Leading Research with Real-World Impact! 4

5 ATMs run on symmetric-key technology
Cryptographic Technology Symmetric-key encryption Symmetric-key message authentication codes (MAC) Public-key encryption Public-key digital signatures Public-key key agreement Message digests (hash functions) Public-key certificates Challenge-response authentication SSL uses all of these ATMs run on symmetric-key technology © Ravi Sandhu World-Leading Research with Real-World Impact! 5

6 Traditional formulation
Cryptographic Services confidentiality traffic flow confidentiality integrity authentication non-repudiation Traditional formulation © Ravi Sandhu World-Leading Research with Real-World Impact! 6

7 Cryptographic Services
confidentiality crypto keys leak profusely via side channels integrity + authentication no point having one without the other non-repudiation requires asymmetric cryptography stronger form of integrity + authentication replay protection beyond integrity? Important insights © Ravi Sandhu World-Leading Research with Real-World Impact! 7

8 Safe Cryptography Symmetric-key cryptography Public-key cryptography
128 bit or higher Public-key cryptography 2048 bit or higher Message digests 256 bit or higher These numbers keep increasing © Ravi Sandhu World-Leading Research with Real-World Impact! 8

9 Symmetric Encryption World-Leading Research with Real-World Impact!
© Ravi Sandhu World-Leading Research with Real-World Impact!

10 Symmetric-Key Encryption
INSECURE CHANNEL Plain- text Plain- text Ciphertext Encryption Algorithm E Decryption Algorithm D A B Symmetric Key shared by A and B K K SECURE CHANNEL Confidentiality Integrity © Ravi Sandhu World-Leading Research with Real-World Impact! 10

11 Symmetric-Key Encryption
confidentiality depends only on secrecy of the key size of key is critical Symmetric key systems do not scale well with N parties we need to generate and distribute N*(N-1)/2 keys A and B can be people or computers © Ravi Sandhu World-Leading Research with Real-World Impact! 11

12 Master Keys and Session Keys
master keys, long lifetime prolonged use increases exposure session keys short-term keys communicated by means of master symmetric keys public key technology © Ravi Sandhu World-Leading Research with Real-World Impact! 12

13 Cryptanalysis ciphertext only known plaintext chosen plaintext
cryptanalyst only knows ciphertext known plaintext cryptanalyst knows some plaintext-ciphertext pairs chosen plaintext chosen ciphertext © Ravi Sandhu World-Leading Research with Real-World Impact! 13

14 Known-Plaintext Attack
40 bit key requires 239  5 * 1011 trials on average (exportable from USA, early 1990’s) trials/second time required ,000 years years days minutes seconds © Ravi Sandhu World-Leading Research with Real-World Impact! 14

15 Known-Plaintext Attack
56 bit key requires 255  3.6 * 10^16 trials on average (DES, 1977) trials/second time required years years years year hours © Ravi Sandhu World-Leading Research with Real-World Impact! 15

16 Known-Plaintext Attack
80 bit key requires 279  6 * 1023 trials on average (SKIPJACK, mid-1990s) trials/second time required years years years years years © Ravi Sandhu World-Leading Research with Real-World Impact! 16

17 Known-Plaintext Attack
128 bit key requires 2127  2 * 1038 trials on average (AES-128, 2001) trials/second time required years years years years years © Ravi Sandhu World-Leading Research with Real-World Impact! 17

18 AES Advanced encryption standard, 2001 3 key sizes: 128, 192, 256
DES, 1977: designed by IBM. Blessed by NSA. SKIPJACK, early 1990s: designed by NSA, declassified 1998 AES, 2001: designed by open international competition, winner was a European team 3 key sizes: 128, 192, 256 Block size: 128 Previously most (e.g. DES) used 64 bit block size 128 bit block size is safer due to birthday attack © Ravi Sandhu World-Leading Research with Real-World Impact! 18

19 Symmetric-Key Encryption
INSECURE CHANNEL Plain- text Plain- text Ciphertext Encryption Algorithm E Decryption Algorithm D A B Symmetric Key shared by A and B K K SECURE CHANNEL Confidentiality Integrity © Ravi Sandhu World-Leading Research with Real-World Impact! 19

20 A B Password Derived Keys INSECURE CHANNEL Plain- text Plain- text
Ciphertext Encryption Algorithm E Decryption Algorithm D A B K K Symmetric Key shared by A and B Key Derivation Function Key Derivation Function Password (salted) Password (salted) © Ravi Sandhu World-Leading Research with Real-World Impact! 20

21 A B Password Derived Keys Dictionary attack INSECURE CHANNEL Plain-
text Plain- text Ciphertext Encryption Algorithm E Decryption Algorithm D A B K K Symmetric Key shared by A and B Key Derivation Function Key Derivation Function Dictionary attack Password (salted) Password (salted) © Ravi Sandhu World-Leading Research with Real-World Impact! 21

22 Perfect Secrecy Vernam one-time pad Plain- text Ciphertext Plain- text
+ + Mi Mi A B AB Symmetric Key Ki Ki Vernam one-time pad SECURE CHANNEL © Ravi Sandhu World-Leading Research with Real-World Impact! 22

23 Double DES Intermediate Ciphertext Plain- text Cipher- text E E X Not covered in lecture K1 K2 effective key size is only 57 bits due to meet-in-the-middle attack © Ravi Sandhu World-Leading Research with Real-World Impact! 23

24 Triple DES Cipher- text Plain- text E D E X Not covered in lecture K1 K2 K1 effective key size is 112 bits due to meet-in-the-middle attack © Ravi Sandhu World-Leading Research with Real-World Impact! 24

25 Electronic Code Book (ECB) Mode
128 bit Data block 128 bit key 128 bit key D E 128 bit encrypted Data block 128 bit Data block OK for small messages identical data blocks will be identically encrypted © Ravi Sandhu World-Leading Research with Real-World Impact! 25

26 Cipher Block Chaining (CBC) Mode
128 bit Data block + 128 bit previous ciphertext block 128 bit key 128 bit key D E  is the exclusive OR operation 128 bit previous ciphertext block + 128 bit Data block © Ravi Sandhu World-Leading Research with Real-World Impact! 26

27 Message Authentication Code (MAC)
Symmetric-Key Message Authentication Code (MAC) © Ravi Sandhu World-Leading Research with Real-World Impact!

28 Message Authentication Code
INSECURE CHANNEL Plaintext + MAC Plain- text Yes/No MAC Algorithm M Verification Algorithm V A B K K © Ravi Sandhu World-Leading Research with Real-World Impact! 28

29 Does not provide non-repudiation
Message Authentication Code INSECURE CHANNEL Plaintext + MAC Plain- text Yes/No MAC Algorithm M Verification Algorithm V A B K K Does not provide non-repudiation © Ravi Sandhu World-Leading Research with Real-World Impact! 29

30 Message Authentication Code
Symmetric Encryption Based Message-Digest Based © Ravi Sandhu World-Leading Research with Real-World Impact! 30

31 Will revisit after discussing message digests
Message Authentication Code Symmetric Encryption Based Message-Digest Based Will revisit after discussing message digests © Ravi Sandhu World-Leading Research with Real-World Impact! 31

Download ppt "Cryptography Basics and Symmetric Cryptography"

Similar presentations

Symmetric Message Authentication Codes Prof. Ravi Sandhu.

Symmetric Message Authentication Codes Prof. Ravi Sandhu.
Symmetric Encryption Prof. Ravi Sandhu.

Symmetric Encryption Prof. Ravi Sandhu.
Asymmetric Encryption Prof. Ravi Sandhu. 2 © Ravi Sandhu PUBLIC KEY ENCRYPTION Encryption Algorithm E Decryption Algorithm D Plain- text Plain- text Ciphertext.

Asymmetric Encryption Prof. Ravi Sandhu. 2 © Ravi Sandhu PUBLIC KEY ENCRYPTION Encryption Algorithm E Decryption Algorithm D Plain- text Plain- text Ciphertext.
PKI Introduction Ravi Sandhu 2 © Ravi Sandhu 2002 CRYPTOGRAPHIC TECHNOLOGY PROS AND CONS SECRET KEY SYMMETRIC KEY Faster Not scalable No digital signatures.

PKI Introduction Ravi Sandhu 2 © Ravi Sandhu 2002 CRYPTOGRAPHIC TECHNOLOGY PROS AND CONS SECRET KEY SYMMETRIC KEY Faster Not scalable No digital signatures.
MAC Raushan. DES simple fiestel network 3131 PlainText Blocks 2*4=8bits 31 f f =0011 xor 0011=0000 = 0 f(r,k)=(2*r+k^2)%8 f(1,5)=(2*1+5^2)%8=3 xor 3 3.

MAC Raushan. DES simple fiestel network 3131 PlainText Blocks 2*4=8bits 31 f f =0011 xor 0011=0000 = 0 f(r,k)=(2*r+k^2)%8 f(1,5)=(2*1+5^2)%8=3 xor 3 3.
Computer Science CSC 474By Dr. Peng Ning1 CSC 474 Information Systems Security Topic 2.1 Introduction to Cryptography.

Computer Science CSC 474By Dr. Peng Ning1 CSC 474 Information Systems Security Topic 2.1 Introduction to Cryptography.
CS 6262 Spring 02 - Lecture #7 (Tuesday, 1/29/2002) Introduction to Cryptography.

CS 6262 Spring 02 - Lecture #7 (Tuesday, 1/29/2002) Introduction to Cryptography.
Chapter 5 Cryptography Protecting principals communication in systems.

Chapter 5 Cryptography Protecting principals communication in systems.
BY MUKTADIUR RAHMAN MAY 06, 2010 INTERODUCTION TO CRYPTOGRAPHY.

BY MUKTADIUR RAHMAN MAY 06, 2010 INTERODUCTION TO CRYPTOGRAPHY.
Fall 2010/Lecture 311 CS 426 (Fall 2010) Public Key Encryption and Digital Signatures.

Fall 2010/Lecture 311 CS 426 (Fall 2010) Public Key Encryption and Digital Signatures.
Chapter 8.  Cryptography is the science of keeping information secure in terms of confidentiality and integrity.  Cryptography is also referred to as.

Chapter 8.  Cryptography is the science of keeping information secure in terms of confidentiality and integrity.  Cryptography is also referred to as.
Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Network Security (A Very Brief Introduction)

Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Network Security (A Very Brief Introduction)
Key Management Workshop November 1-2, 2001. 3. Cryptographic Algorithms, Keys, and other Keying Material  Approved cryptographic algorithms  Security.

Key Management Workshop November 1-2, Cryptographic Algorithms, Keys, and other Keying Material  Approved cryptographic algorithms  Security.
CS526: Information Security Prof. Sam Wagstaff September 16, 2003 Cryptography Basics.

CS526: Information Security Prof. Sam Wagstaff September 16, 2003 Cryptography Basics.
Dr. Reuven Aviv, Nov 2008 Conventional Encryption 1 Conventional Encryption & Message Confidentiality Acknowledgements for slides Henric Johnson Blekinge.

Dr. Reuven Aviv, Nov 2008 Conventional Encryption 1 Conventional Encryption & Message Confidentiality Acknowledgements for slides Henric Johnson Blekinge.
McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Security.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2004 Security.
Lecture 2: Introduction to Cryptography

Lecture 2: Introduction to Cryptography
CRYPTOGRAPHY Cryptography is art or science of transforming intelligible message to unintelligible and again transforming that message back to the original.

CRYPTOGRAPHY Cryptography is art or science of transforming intelligible message to unintelligible and again transforming that message back to the original.
CS/ECE 578 Cyber-Security Dr. Attila Altay Yavuz

CS/ECE 578 Cyber-Security Dr. Attila Altay Yavuz
Reviews Rocky K. C. Chang 20 April 2007.

Reviews Rocky K. C. Chang 20 April 2007.

Similar presentations

Ads by Google