encryption and decryption ,and its types

encryption and decryption ,and its types

1. ENCRYPTION AND DECRYPTION Presented By:- Anchal Bhardwaj (0581522008) And Ruchi Jain(0161522008)

2. OUTLINE Introduction Encryption Decryption Algorithms Symmetric Encryption DES Algorithm Asymmetric Encryption RSA Algorithm Comparison Summary References BACK NEXT

3. INTRODUCTION Cryptography is the science of information security. The word is derived from the Greek  kryptos , meaning hidden. Cryptography components:- Plain Text Cipher Text Encryption Decryption BACK HOME NEXT

4. Plaintext : It is original intelligible message , before being transformed .The data are not encrypted. Ciphertext : After the message is transformed . The data are encrypted. Alice : Alice is the person who needs to send secure data. Bob : Bob is the recipient of the data. Eve : Eve is the person who somehow disturbs the communication between Alice and Bob. BACK HOME NEXT

5. ENCRYPTION DECRYPTION PLAIN TEXT CIPHERTEXT PLAIN TEXT SENDER RECEIVER EVE DATA FLOW DIAGRAM BACK HOME NEXT

6. ENCRYPTION It is the process in which plaintext or data is converted into unintelligible form by means of a reversible translation, based on a translation table or algorithm . BACK HOME NEXT Encrypted Text Original Text + Key = Encryption

7. DECRYPTION It is the proces in which encrypted text or data (called ciphertext ) is translated back into the original text or data (called plaintext). Encrypted Text Original Text Key + = Decryption BACK HOME NEXT

8. ALGORITHMS Symmetric Encryption(Conventional Encryption) Asymmetric Encryption(Public-key Encryption) BACK HOME NEXT

9. Symmetric Encryption Same algorithm with same key(secret key) is used for encryption and decryption. Sender and receiver must share the algorithm and the key. Secret key BACK HOME NEXT Plaintext Encryption Decryption Plaintext Ciphertext

10. Secret-Key Problem? All keys need to be replaced, if one key is compromised. Not practical for the Internet environment. On the other hand, the encryption speed is fast. Suitable to encrypt your personal data. 10 BACK HOME NEXT

11. Symmetric encryption algorithms Algorithm Name Key Length (bits) Blowfish Up to 448 DES 56 IDEA 128 RC2 Up to 2048 RC4 Up to 2048 RC5 Up to 2048 Triple DES 192 BACK HOME NEXT

12. DES Algorithm The data encryption standard (DES) was developed in the 1970s by the NATIONAL BUREAU OF STANDARDS (NBS) with the help of the NATIONAL SECURITY AGENCY (NSA). Most widely used encryption algorithm until recently. Exhibits the classic Feistel Structure. Uses a 64-bit block and a 56-bit key. BACK HOME NEXT

13. Asymmetric encryption One algorithm is used for encryption and decryption with a pair of keys, one for encryption and one for decryption. Sender and receiver must each have one of the matched pair of keys(not the same one). BACK HOME NEXT Public key Plaintext Encryption Decryption Ciphertext Plaintext Private key

14. Public-Private Encryption First, create public and private key Public key Private key Private key Private key stored in your personal computer Public Key Directory Public Key Public key stored in the directory BACK HOME NEXT

15. Message Encryption ( User A sends message to User B ) Public Key Directory Text User A User B ’ s Public Key Encryption Encrypted Text BACK HOME NEXT

16. Decryption with your Private key Encrypted Text User B ’ s Private key Private key stored in your personal computer Decryption Original Text User B BACK HOME NEXT

17. Asymmetric algorithms Algorithm Name Key Length (bits) DSA Up to 448 El Gamal 56 RSA 128 Diffie-Hellman Up to 2048 BACK HOME NEXT

18. RSA Algorithm Published in the paper A Method for Obtaining Digital Signatures and Public-Key Cryptosystems   in 1977 by Ron Rivest , Adi Shamir and Len Adleman . Most widely accepted and implemented general- purpose approach to public-key encryption . B lock cipher scheme in which the plaintext and cipher text are integers between 0 and n-1 for some n(1024 bits). BACK HOME NEXT

19. Key Generation Choose two distinct prime numbers  p  and  q . For security purposes, the prime integers p  and  q  should be chosen uniformly at random and should be of similar bit-length. Compute  n  =  pq . n  is used as the modulus for both the public and private keys. Compute  φ ( pq ) = ( p  − 1)( q  − 1). ( φ   is Euler's totient function). BACK HOME NEXT

20. Choose a small integer e, such that 1<e< φ (n). e is coprime to φ (n) i.e GCD(e, φ (n)). Determine d which satisfies the congruence relation:- de=1(mod φ (n)), Where d< φ (n). P ublish their public encryption key: PU={ e,n }. Keep secret private decryption key: PR={ d,n }. CONTINUED… BACK HOME NEXT

21. Encryption M Plaintext, M<n C Ciphertext C=M e mod N De cryption M= C d mod N BACK HOME NEXT

22. RSA Example Select primes: p=7 and q=19. Compute n = p * q = 7 * 19 = 133. Compute ø( n )=( p– 1)( q- 1)=6 × 18=108. Select e such that GCD(e,108)=1 for e =2, GCD(2,108)=2 (no) for e =3, GCD(3,108)=3 (no) for e =4, GCD(4,108)=4 (no) for e =5, GCD(5,108)=1 (yes!) Thus, choosing e=5 . BACK HOME NEXT

23. CONTINUED… Determine d: de mod φ (n)=1 and d < φ (n). this is equivalent to de=1+k φ (n). where k is any integer. for k=0, d=1/5 (no) for k=1, d=109/5 (no) for k=2, d=217/5 (no) for k=3, d=325/5 =65 (yes!) Resulting keys: Public Key Private Key PU={ e,n }={5,133}. PR={ e,n }={65,133}. BACK HOME NEXT

24. Given Message, M=88. Encryption:- Decryption:- CONTINUED… C=M e mod N = 88 5 mod 133 =5277319168 mod 133 =65. M= C d mod N =65 65 mod 133 BACK HOME NEXT

25. =65* (65) 64 mod 133 =65* (65 2 ) 3 2 mod 133 = 65* (4225) 3 2 mod 133 =65* (4225 mod 133) 3 2 mod 133 = 65* (102) 3 2 mod 133 = 65* (102 2 ) 16 mod 133 = 65* (10404 mod 133) 16 mod 133 = 65* (30) 16 mod 133 = 65* (900 mod 133) 8 mod 133 =65* (102) 8 mod 133 CONTINUED… BACK HOME NEXT

26. = 65* (102 2 ) 4 mod 133 = 65* (10404 mod 133) 4 mod 133 = 65* (30) 4 mod 133 = 65* (900 mod 133) 2 mod 133 = 65* (102) 2 mod 133 = 65* 10404 mod 133 =676260 mod 133 =88 (Original Message) CONTINUED… BACK HOME NEXT

27. RSA Security Three approaches to attacking RSA: brute force key search (infeasible given size of numbers) mathematical attacks (based on difficulty of computing ø(N), by factoring modulus N) timing attacks (on running of decryption)

28. Advantages Increased security and convenience. Provide digital signatures that cannot be repudiated. Best used in multi-user environment. Dis dvantages About 1000 times slower than DES. Computational cost is high.

29. SYMMETRIC ENCRYPTION ASYMMETRIC ENCRYPTION Same algorithm with the same key is used for encryption and decryption. One algorithm is used for encryption and decryption with a pair of keys, one for encryption and other for decryption. Sender and receiver must share the algorithm and the key. Sender and receiver must each have one of the matched pair of keys(not the same one). Key must be kept secret. One of the two keys must be kept secret. Faster as compared to asymmetric encryption. About 1000 times slower than symmetric encryption. Generally more secure and less computationally less expensive . Less secure and computational cost is relatively high. Best used f or digital signatures and for protecting DES keys. Best used for Bulk data encryption . BACK HOME NEXT Comparison

30. Summary Cryptography Encryption Decryption Algorithms Symmetric encryption DES Asymmetric encryption RSA Comparison BACK HOME NEXT

31. References “Cryptography and Network Security” by William Stallings. “Computer Networks” by Andrew S. Tanenbaum . Google.com. Wikipedia.com BACK HOME NEXT

32. END SHOW