Network Security

1. DATA ENCRYPTION
STANDARD(DES)
NAME:A.JENIFER
CLASS:II-M.Sc.,(COMPUTER SCIENCE)
BATCH:2017-2019
INCHARGE STAFF:MS.M.FLORENCE DAYANA

2. The DESwas once a predominant symmetric key
algorithm for the encryption data. It was highly
influential in the advancement of modern
cryptography in the academic world.
Issued in 1977 by the National Bureau of
Standards as Federal Information Processing
Data Encryption Standard (DES)

3. Algorithm itself is referred to as the Data
Encryption Algorithm (DEA)
◦ There are two inputs to the encryption function. The
plaintext to be encrypted and thekey.
◦ Data are encrypted in 64-bit blocks using a 56-bit key
◦ The algorithm transforms 64-bit input in a seriesof
steps into a 64-bit output
◦ The same steps, with the same key, are used toreverse
the encryption
DES

5. DESblock cipher

6. DESEncryption Algorithm
1.The left hand side of the figure, the
plaintext proceeds in threephases.
2.First, 64 bit plaintext passes
through an initial permutation(IP) that
rearranges the bit produce the
permuted input.
3.The phase consisting of sixteen
rounds of the same function, which
involves both permutation and
substitution functions.
4.The output of the last round
consists of 64 bits that are afunction
of input plaintext and akey.
5.The left & right halves of the output
are swapped to produce the pre-
output.

7. Avalanche in DES

9. 1. The use of 56-bit keys:
In computing, 56-bit encryption refers to a key size of fifty-
six bits, or seven bytes, for symmetric encryption, with the key
length of 56 bits, there are
256 possible keys,which is approximately 7.2 *
106 keys.
On average, half of the key space has to be searched, a single
machine performing one DESencryption per micro second
would take more than a thousand years to break the cipher.
THE STRENGTH OF DES

10. The focus of concern has been on the eight substitution
tables, S-Boxes, that are used in eachiteration.
Because the design criteria for these boxes, and indeed
for the entire algorithm, were not made public, there is a
suspicion that the boxes were constructed in such a way
that cryptanalysis is possiblefor an opponent who
knows the weakness in theS-boxes.
2. The Nature of the DESalgorithm:

11. The timing attacks relate to public keyalgorithms.
The timing attack is one in which information about the
key or the plaintext is obtained by observing how long it
takes a given implementation to perform decryptions on
various cipher texts
The timing attack Exploits the fact that an encryption or
decryption algorithm often takes slightly different
amounts of time on different inputs
3. Timing attacks

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