Data Encryption Standard (DES)

Data Encryption Standard (DES)

1. Data Encryption Standard (DES) Muhammad Haris Ahmed [email protected] 12cs45

2. Symmetric Systems Several types of symmetric algorithms are used today. They have different methods of providing encryption and decryption functionality The one thing they all have in common is that they are symmetric algorithms, meaning the sender and receiver are using two instances of the same key

3. Symmetric Algorithms Data Encryption Standard (DES) 3DES (Triple DES) Blowfish Twofish IDEA (International Data Encryption Algorithm) RC4, RC5, RC6 AES (Advanced Encryption Standard) SAFER (Secure and Fast Encryption Routine

4. DES First Break! In 1998, the Electronic Frontier Foundation built a computer system for $250,000 that broke DES in three days by using a brute force attack against the keyspace

5. DES First Break! It contained 1,536 microprocessors running at 40MHz, which performed 60 million test decryptions per second per chip

6. What is DES? DES Use Symmetric system means both sender and receiver side we used same key for encryption and decryption.

7. What is DES? DES used 64 bits of block for encryption and decryption. Sixteen rounds of transposition and substitution are performed in order to achieve DES.

8. DES Advancement Cycle

9. How Does DES Work ? DES is a symmetric block encryption algorithm. When 64-bit blocks of plaintext go in, 64-bit blocks of cipher text come out. It is also a symmetric algorithm, meaning the same key is used for encryption and decryption . It uses a 64-bit key: 56 bits make up the true key, and 8 bits are used for parity .

10. How Does DES Work ? …. When the DES algorithm is applied to data, it divides the message into blocks and operates on them one at a time. The blocks are put through 16 rounds of transposition and substitution functions . The result is 64-bit blocks of ciphertext .

11. DES Modes Block ciphers have several modes of operation. Each mode specifies how a block cipher will operate.

12. DES Modes Electronic Code Book (ECB) Cipher Block Chaining (CBC) Cipher Feedback (CFB) Output Feedback (OFB) Counter Mode (CTR)

13. It Inherit core functionality from their parent block which is Symmetric System. Like 64 bits of block use for encryption and decryption. Use Same key for encryption and decryption of all blocks of data. Electronic Code Book Mode

14. Electronic Code Book Mode

15. User for the Small amount of text not for large amount of data. Reason Same block of plain text and key generate same cypher text each time Easy to find Pattern with large amount of data Electronic Code Book Mode

16. Electronic Code Book Mode ECB mode operates like a code book. A 64-bit data block is entered into the algorithm with a key, and a block of ciphertext is produced For a given block of plaintext and a given key, the same block of ciphertext is always produced ECB is the easiest and fastest mode to use, but as we will see, it has its dangers

17. Electronic Code Book Mode… So, two bad things can happen here: An attacker could uncover the key and thus have the key to decrypt all the blocks of data, or An attacker could gather the ciphertext and plaintext of each block and build the code book that was used, without needing the key.

18. Cipher Block Chaining Mode Cipher Block Chaining (CBC) does not reveal a pattern, because each block of text, the key, and the value based on the previous blocks. This results in more random ciphertext This provides dependence between the blocks, in a sense chaining them together

19. Cipher Block Chaining Mode

20. Cipher Block Chaining Mode This chaining effect means that a particular ciphertext block is dependent upon all blocks before it, not just the previous block. When we encrypt our very first block using CBC, we do not have a previous block of ciphertext If we do not add a piece of randomness when encrypting this first block to save from hackers.

21. So, The solution is to use Initialization Vector that generate randomness in first block. Cipher Block Chaining Mode

22. Cipher Feedback Mode (CFB) The CBC mode is great to use when you need to send large chunks of data at a time but when the need of send small amount of data at a time we use CFB. Cipher Feedback is the combination of block cipher and stream cipher.

23. Cipher Feedback Mode (CFB) Keep One copy of Cipher text.

24. Difference Between CFB & CBC Major Difference between both of them is CBC works with 64 bits of data only but CFB also work with 8 bits or so on.

25. Difference Between CFB & CBC

26. Output Feedback Mode It Cover the weakness of Cipher feedback mode. Almost Same process of encryption and decryption.

27. Output Feedback Mode It’s similar to the Cipher Block Chaining Mode but there is one minor changing in it.

28. Difference in OFB & CFB

29. Counter Mode (CTR) T here is no chaining involved in Counter Mode (CTR) like other three types. Cipher block Chaining. Cipher Feedback. Output Feeback .

30. Counter Mode (CTR) Each block is individually decrypted without depending on other blocks. the encryption of the individual blocks can happen in parallel, which increases the performance.

31. Counter Mode (CTR) No use of initialization Vector instead it use counter.

32. Thank you