Title: Cryptography Instructor: Dr. Yanqing Zhang Presented by: Jiangling, Yin

1. Department of Computer Science Georgia State University Title: Cryptography Instructor: Dr. Yanqing Zhang Presented by: Jiangling,Yin CSC 8320 Advanced Operating Systems

2. Outline • Introduction & Motivation • What is cryptography and why it is necessary? • Modern cryptography • Private Key Cryptosystem • Public Key Cryptosystem • Comparison of Cryptographic Systems • Future work

3. A Simple Example • Suppose two lovers try to meet at a certain place. And the girl sends the information to the boy: meet me at ###

4. A Simple Example • Instead of sending the intelligible message to the boy, the girl plays a trick and change the information. meet me at ### phhw ph dw fv ghvduwphqw

5. A Simple Example • The boy receives the girl’s message and thinking…. phhw ph dw fv ghvduwphqw ???

6. A Simple Example • If the boy happens to know Cryptography, and he may do following things… phhw ph dw fv ghvduwphqw !!!!! meet me at CS department

7. A Simple Example • Finally…. Meet at CS department ???? VWXSLW What is VWXSLW ?

8. So, What Is Cryptography • To make thing hard to understand if you don’t know the behind principles… • To convertintelligible information intounintelligible. • To hidden information.

9. Application Model of Cryptography • B and A (lovers!) want to communicate “securely” • C (intruder) may intercept, delete, add messages A B data, control messages channel secure sender secure receiver data data C

10. Who Might B, A be? • Distributing OS authenticated principals • Web browser/server for electronic transactions (e.g., on-line purchases) • on-line banking client/server • DNS servers • routers exchanging routing table updates

11. A’s encryption key B’s decryption key encryption algorithm decryption algorithm ciphertext plaintext plaintext K K A B The Language of Cryptography m plaintext message KA(m) ciphertext, encrypted with key KA m = KB(KA(m))

12. Mapping Language Into The Example • Encryption (decryption) algorithm : substitute one letter for another • Plaintext: meet me at CS department • Ciphertext: phhw ph dw fv ghvduwphqw • Key: the mapping from the set of 26 letters to the set of 26 letters

13. A’s encryption key B’s decryption key encryption algorithm decryption algorithm ciphertext plaintext plaintext K K A B Private & Public Key Cryptosystems • Symmetric key cryptography: • && are identical. • The keys must be kept secret. • The encryption and decryption functions used can be the same or different. • Public key cryptography: • && are different (one public, the other private). K K A B K K A B

14. Symmetric Key Cryptography: Examples • Examples: • ROT13: Very simple rotation algorithm • Caesar cipher: Another (better) rotation algorithm • crypt: Original Unix encryption program • DES: Data Encryption Standard [NIST 1993] • AES: Advanced Encryption Standard • Skipjack: U.S. National Security Agency developed algorithm (classified) • DES: Data Encryption Standard • In 1997 DES was cracked in only 140 days by a team • In 1999 DES was cracked in little over 22 hours by a network of volunteers and special purpose computer.

15. K K A-B A-B encryption algorithm decryption algorithm ciphertext plaintext plaintext message, m K (m) A-B K (m) m = K ( ) A-B A-B Symmetric Key Cryptography: Key Issues • How do sender and receiver agree on key value? • How is the agreed upon key distributed to both sender and receiver in a secure fashion?

16. Public Key Encryption • Diffie-Hellman 1976: the first public key approach proposed. • Sender and receiver do notshare secret key • Public key is available to every one • Private key is known by only receiver

17. + K (m) B - + m = K (K (m)) B B Public key cryptography + B’s public key K B - B’s private key K B encryption algorithm decryption algorithm plaintext message plaintext message, m ciphertext

18. K (K (m)) = m B B - + 1 2 Public key encryption algorithms Requirements: need K ( ) and K ( ) such that . . + - B B + given public key K , it should be impossible to compute private key K B - B RSA:Rivest, Shamir, Adelson algorithm

19. + - K K B B RSA: Creating public/private key pair 1. Choose two large prime numbers p, q. (e.g., 1024 bits each) 2. Compute n = pq, z = (p-1)(q-1) 3. Choose e (with e<n) that has no common factors with z. (e, z are “relatively prime”). 4. Choose d such that ed-1 is exactly divisible by z. (in other words: ed mod z = 1 ). 5.Public key is (n,e).Private key is (n,d).

20. 1. To encrypt message m (<n), compute d e c = m mod n m = c mod n d e m = (m mod n) mod n RSA: Encryption, decryption 0. Given (n,e) and (n,d) as computed above 2. To decrypt received bit pattern, c, compute Magic happens! c

21. d e m = c mod n c = m mod n d c RSA example: Bob chooses p=5, q=7. Then n=35, z=24. e=5 (so e, z relatively prime). d=29 (so ed-1 exactly divisible by z). Encrypting 8-bit messages. e m m bit pattern encrypt: 00001100 17 24832 12 c decrypt: 17 12 481968572106750915091411825223071697

22. Why does RSA work? • Must show that cd mod n = m where c = me mod n • Fact: for any x and y: xy mod n = x(y mod z) mod n • where n= pq and z = (p-1)(q-1) • Thus, cd mod n = (me mod n)d mod n = med mod n = m(ed mod z) mod n = m1 mod n = m

23. Comparison of Cryptographic Systems • With suitable keys and algorithms, both methods can be secure enough for most purposes. • To use symmetric cryptography, both parties must know the secret key, which can be quite inconvenient. • To use public key cryptography, one only needs to find the public key to communicate with someone else, which can be a lot more convenient. • Encrypting and decrypting a lot of information with public key cryptography can be painfully slow in comparison to symmetric cryptography.

24. Ongoing / Future Work ---key security KEY security is very important. Cryptography based on Image or watermarking Application in wireless environment.

25. Quantum Cryptography • Apply the phenomena of quantum physics • Relies on • The Heisenberg Uncertainty principle • The principle of photon polarization Mehrdad S. Sharbaf,” Quantum Cryptography: A New Generation of Information Technology Sec urity System”, 2009 IEEE[2]. Mehrdad S. Sharbaf,” Quantum Cryptography: A New Generation of Information Technology Sec urity System”, 2009 IEEE

26. Quantum Cryptography (contd.) • Why Quantum Cryptography is secure? • when measuring the polarization of a photon, the choice of what direction to measure affects all subsequences measurements. • photons can be easily polarized (by photon polarization principle) • intruder can not copy unknown qubits (no-cloning theorem). • presence of the intruder can be determined • Harvard, and Boston University built the DARPA quantum network, the world’s first network that delivers end-to-end network security via highspeed quantum key distribution, and tested that network against sophisticated eavesdropping attacks.

27. Cryptography Based on Watermarking • International Journal of Computer Science and Security (IJCSS), Volume (1) : Issue (3), 2011 SonalChugh & Mr. Rajesh Malik, Quality Improvement of Grey Scale and Color Images Using Cryptography and Robust Watermarking, International Journal of Computer Science and Security (IJCSS), Volume (1) : Issue (3), 2011

28. Application in wireless environment • User authentication is a crucial service in wireless sensor networks (WSNs) wireless sensor nodes are typically deployed in an unattended environment, leaving them open to possible hostile network attack. • However, wireless sensor nodes are limited in computing power, data storage and communication capabilities, any user authentication protocol must be designed to operate efficiently in a resource constrained environment. Yeh, H.-L.; Chen, T.-H.; Liu, P.-C.; Kim, T.-H.; Wei, H.-W. A Secured Authentication Protocol for Wireless Sensor Networks Using Elliptic Curves Cryptography. Sensors2011, 11, 4767-4779.

29. Cryptography toolkit • http://nsfsecurity.pr.erau.edu/crypto/generichash.html • http://ats.oka.nu/titaniumcore/js/crypto/Cipher.sample.html • http://www.privacycrypt.com/ • https://www.dlitz.net/software/pycrypto/ TRY…