- DES (Data Encryption Standard) is a symmetric block cipher algorithm that encrypts data in 64-bit blocks using a 56-bit key. It was the first encryption standard adopted by the U.S. government for protecting sensitive unclassified federal government information. - DES works by performing 16 rounds of complex substitutions and permutations on each data block, encrypting it using the key. It has various modes of operation like ECB, CBC, CFB, OFB, and CTR that specify how it operates on data. - In 1998, DES was broken using a brute force attack by the Electronic Frontier Foundation in just 3 days, showing the need for stronger algorithms like AES which replaced DES as the encryption standard

1. DATA ENCRYPTION
STANDARD (DES)
MUHAMMAD HARIS AHMED
M.HARIS@STU.SMIU.EDU.PK
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)
• There is no chaining involved in Counter Mode
(CTR) like other three types.
I. Cipher block Chaining.
II. Cipher Feedback.
III. 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