This document provides an overview of data encryption. It defines encryption as disguising information so that only those with the key can recover it. Encryption involves encrypting cleartext into ciphertext using an encryption key. Symmetric encryption uses the same key for encryption and decryption, while asymmetric encryption uses different keys. Encryption methods include transposition, which rearranges bits or characters, and substitution, which replaces them. The document discusses the Data Encryption Standard (DES) and RSA public key cryptosystem algorithms. It concludes that public key encryption can provide both privacy and authentication.

1. Data
Encryption
Arvind Rana
Lecturer Computer Science
SVSD PG College Bhatoli, Distt Una, H.P.

5. 
Encryption Definition:
 The
action of disguising 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.
Arvind Rana, Lecturer Computer Science

6. A
message is cleartext (plaintext) is encrypted
(disguised) through the use of an encryption key
to create a Ciphertext.
Arvind Rana, Lecturer Computer Science

7.  The
encryption key may be changed from time to
time to make an intruder’s task more difficult.
 Restoration of a ciphertext to cleartext is
achieved by the action of decryption using a
decryption key.
Arvind Rana, Lecturer Computer Science

8. 
In symmetric (Single key):
 The
encryption and decryption keys are the
same.

In asymmetric (two keys):
 The
encryption and decryption keys are
different.
Arvind Rana, Lecturer Computer Science

9. 
Encryption Methods:
 Encryption
is accomplished by scrambling the
bits, characters, words, or phrases in the original
message. Scrambling involves two activities:


Transposition
Substitution
Arvind Rana, Lecturer Computer Science

10. 
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.
Arvind Rana, Lecturer Computer Science

11. 
Data Encryption Standard (DES):
 Most
widely used algorithm
 Pioneered by IBM
 It is symmetric cryptosystem
 Developed to protect sensitive, unclassified, US
government, Computer data.
 Used to provide authentication of electronic
funds transfer messages.
Arvind Rana, Lecturer Computer Science

12. 
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 (L 0) 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.
Arvind Rana, Lecturer Computer Science

13. 
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.
Arvind Rana, Lecturer Computer Science

14. 
Public key encryption can achieved:
 Privacy
 Authentication

15. Arvind Rana
Lecturer Computer Science
SVSD PG College Bhatoli,
Distt. Una, H.P.