DES - Data Encryption Standard | Data Encryption Standard In Cryptography | Simp

2. Today’s Agenda What Is DES? Origin of DES Feistel Ciphers How DES Works Future of DES Live Example

3. What Is DES?

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5. What Is DES? • Stands for Data Encryption Standard • Symmetric-Key algorithm using block-by-block encryption • Block size is 64 bits and key size is 48 bits • Follows the Feistel Cipher structure Block 1 Block 2 Block n Plaintext Broken down to 64-bit blocks

6. Origin of DES

7. Origin of DES

8. Feistel Ciphers

9. Feistel Ciphers

10. Feistel Ciphers

11. Feistel Ciphers • Block Cipher that is used as a structure for encryption algorithms • Uses substitution and permutation alternately • Based on Shannon Structure from 1945 • Developed by Horst Feistel • Reversing the process can decrypt ciphertext back to plaintext

12. Feistel Ciphers Plaintext (64-bit) Left Half(32-bit) Right Half(32-bit) + XOR Operation F Encryption Key used here New Left Half New Right Half

13. Round Function One Half (32-bit) Expansion Box + 48-bit Text Kn 48-bit Key 48-bit Output

14. Round Function 48-bit Output S-Box XOR’d with the other half of plaintext 32-bit Output

15. Structure Guidelines • Block size should be a compromise between size and speed

16. Structure Guidelines • Block size should be a compromise between size and speed • Key size is directly proportional to strength of encryption

17. Structure Guidelines • Block size should be a compromise between size and speed • Key size is directly proportional to strength of encryption • Higher the number of rounds, tougher it is to crack

18. Structure Guidelines • Block size should be a compromise between size and speed • Key size is directly proportional to strength of encryption • Higher the number of rounds, tougher it is to crack • Round function should be complex

19. Structure Guidelines • Block size should be a compromise between size and speed • Key size is directly proportional to strength of encryption • Higher the number of rounds, tougher it is to crack • Round function should be complex • Speed is essential to handle large amounts of data

20. How DES Works

21. How DES Works – Key Generation 64-bit Plaintext Initial Permutation K0 Round 1 48-bit key K1 56-bit Cipher Key Round 2 Round-key Generator 48-bit key K15 Round 16 48-bit key Final Permutation 64-bit Ciphertext

22. How DES Works - Decryption 64-bit Ciphertext Final Permutation K15 Round 16 48-bit key 56-bit Cipher Key K1 Round-key Generator Round 2 48-bit key K0 Round 1 48-bit key 64-bit Plaintext Initial Permutation

23. Modes of Operation Electronic Codebook Cipher Block Chaining DES Cipher Feedback Block Output Feedback Counter Method

24. Future of DES

25. Future of DES • Replaced by AES in 2002 as the world standard for encryption • 56-bit key size easily broken by new generation computers • Withdrawn support for official purposes in 2005 • Triple-DES still allowed for important data till 2030

26. Live Example