Assignment

1. CRYPTOGRAPHY AND NETWORK
SECURITY
2.2 → Identify and describe the working principle of
simple Data Encryption standard and Triple DES
algorithm in detail.
By,
SURYA SK,
THULASIVASAN V,
VIGNESHEARAN D,
YUVAPRIYA P.

2. DATA ENCRYPTION STANDARD (DES)
 Data encryption standard (DES) has been found
vulnerable to very powerful attacks and therefore, the
popularity of DES has been found slightly on the decline.
 DES is a block cipher and encrypts data in blocks of size
of 64 bits each, which means 64 bits of plain text go as
the input to DES, which produces 64 bits of cipher text.
 The same algorithm and key are used for encryption and
decryption, with minor differences. The key length is 56
bits.

3. CONT…
 We have mentioned that DES uses a 56-bit key. Actually, the initial
key consists of 64 bits. However, before the DES process even starts,
every 8th bit of the key is discarded to produce a 56-bit key. That is bit
positions 8, 16, 24, 32, 40, 48, 56, and 64 are discarded.
 Thus, the discarding of every 8th bit of the key produces a 56-bit
key from the original 64-bit key. DES is based on the two
fundamental attributes of cryptography: substitution and transposition.
 DES consists of 16 steps, each of which is called a round. Each round
performs the steps of substitution and transposition. Let us now
discuss the broad-level steps in DES

4. WORKING…
 In the first step, the 64-bit plain text block is handed over to
an initial Permutation (IP) function. The initial permutation
is performed on plain text.
 Next, the initial permutation (IP) produces two halves of the
permuted block; saying Left Plain Text (LPT) and Right
Plain Text (RPT).
 Now each LPT and RPT go through 16 rounds of the
encryption process. In the end, LPT and RPT are rejoined
and a Final Permutation (FP) is performed on the combined
block.
 The result of this process produces 64-bit cipher text.
 Step 1 : Initial Permutation (IP)
 Step 2 : Initial Permutation (IP) Table

5. TRIPLE DES ALGORITHM
 Triple DES is an encryption technique that uses
three instances of DES on the same plain text.
 It uses there different types of key-choosing
techniques in the first all used keys are different in
the second two keys are the same and one is
different and in the third, all Its eyes are the same.

6. CONT…
 Triple DES is also vulnerable to meet-in-the
middle attack because of which it give total
security level of 2^112 instead of using 168 bit
of key.
 The block collision attack can also be done
because of short block size and using same key
to encrypt large size of text. It is also vulnerable
to sweet32 attack.

7. ENCRYPTION AND DECRYPTION PROCESS
 The encryption-decryption process is as follows ;
 Encrypt the plaintext blocks using single DES with key K1.
 Now decrypt the output of step 1 using single DES with
key K2.
 Finally, encrypt the output of step 2 using single DES with
key K3.
 The output of step 3 is the cipher text. Decryption of a
cipher text is a reverse process. User first decrypt using
K3, then encrypt with K2, and finally decrypt with K1.

8. THANK YOU