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.
5.
6. Encryption Methods:
Encryption is skilled by scrambling( الٹ
پلٹ
کرنا )
the bits, characters, words, or phrases in the
original message. Scrambling involves two
activities:
Transposition ( جگہ
کی
تبدیلی )
Substitution ( قائم
مقام )
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
