Khayam Sarhadi CS University Of swat

1. Data
Encryption
By khayam Sarhadi
Roll No: 130221
BS-CS 7th
UOS

2.  Encryption Definition:
 The action of hiding information so that it can be
recovered easily by the persons who have the
key, but is highly resistant to recovery by
persons who do not have the key.

3.  A message is clear text (plaintext) is encrypted
(disguised) through the use of an encryption key
to create a Cipher text.

4.  In symmetric (Single key):
 The encryption and decryption keys are the
same.
 In asymmetric (two keys):
 The encryption and decryption keys are
different.

6.  Encryption Methods:
 Encryption is skilled by scrambling( ) the bits,
characters, words, or phrases in the original
message. Scrambling involves two activities:
 Transposition ()
 Substitution ()

7.  Transposition:
 In which the order of the bits patterns,
characters, words or phrases is rearranged.
 Substitution:
 In which new bit patterns, characters, words, or
phrases are substituted for the originals without
changing their order.

8.  Data Encryption Standard (DES):
 Most widely used algorithm
 Founded by IBM
 It is symmetric cryptosystem
 Developed to protect sensitive, unclassified, US
government, Computer data.
 Used to provide authentication of electronic
funds transfer messages.

9.  The basic process in
enciphering a

64-bit data block

56-bit key using the DES
consists of:
• An initial permutation (IP)
• 16 rounds of a complex key
dependent calculation f
• A final permutation, being
the inverse of IP

10.  DES Algorithm:
 The algorithm accepts plaintext, P, and performs
an initial permutation, IP, on P producing P0, The
block is then broken into left and right halves, the
Left (L0) being the first 32 bits of P0 and the right
(R0) being the last 32 bits of P0.
 With L0 and R0, 16 rounds are performed until L16 and
R16 are generated.
 The inverse permutation, IP-1
, is applied to L16R16 to
produce ciphertext C.

11.  Public Key Cryptosystem
 It is an asymmetric cryptosystem.
 First announced in 1976.
 Offer a radically different approach to
encryption.
 The idea depends on the use of a pair of keys
that differ in a complementary way.
 Several algorithms are proposed
 RSA algorithm is considered to be highly secure.
Tayyab Arif 00923445064252, Allama Iqbal Open University

12.  Public key encryption can achieved:
 Privacy
 Authentication