Cryptography is a method used for securely storing and transmitting data, ensuring that only intended recipients can access it. The document explores the history, types (symmetric and asymmetric), and techniques of cryptography, including classical and modern methods, along with algorithms like DES and AES. It emphasizes the importance of cryptography in maintaining data confidentiality, integrity, and secure communication across various applications.

1. Cryptography
Subodh B. Pawar
Ruksar I. Shaikh

2. What is Cryptography?
 Cryptography is a method of
storing and transmitting data in a
particular form so that only those
for whom it is intended can read
and process it.
 Cryptography derived its name
from a Greek word called
“Kryptos” which means “Hidden
Secrets”.

3. History of Cryptography
 The earliest forms of cryptography were found in the
cradle of civilization, including the regions currently
encompassed by Greece and Rome.

4. Greece: Wrap a tape around a stick and write the
message on the wound tape.
Rome: Caesar Shift Cipher was used.
It utilized the idea of shifting letters by an agreed upon
number (three was a common historical choice), and thus
writing the message using the letter-shift.

5. Security goals
Secure
Confidentiality
Non-
Repudiatio
n
Authentication
Integrity

6. Encryption and Decryption
Decryption
key,
Decryption
algorithm
Encryption
key
Encryption
algorithm

7. Cryptography
Symmetric key Asymmetric key
cryptography cryptography
(Public key cryptography)
Classical Modern
cryptography cryptography
Transposition Substitution Stream Block
cipher cipher cipher cipher
7

8. Symmetric Key Encryption
•Common Key
•Sharing Prior exchange of info
•Key Needed to be Changed reguraly.
•Length(key) , Computing Power.

9. Challenges:
1.Key Establishment: Secure Key Establishment.
2.Trust Issue: Receiver Lost key to attacker & no
informed.
Solution:
Why did asymmetric key came into picture?
 People needs to exchange information with non-
familier & non-trusted parties.
 Regular Change Of keys->Complex & Cumbersome.
 Pre-sharing of Secret Keys

10. Asymmetric
Encryption Different Keys.
 But Mathematically Related.
 Computationally Not Feasible for attacker.
 Each User
 Pair of Key
 Public Key Encryption
Public key Repository & Private Key Guarded.

11.  Challenges:
 Public key used is really public key of person?
 Solution:
 PKI(public key Infrastructure )
Third Party manages & attest to authenticity of public key

12. Classical Cryptography
1. Transposition:
-In the transposition technique the positions
of in plaintext is changed with one another.
e.g Plain text: MEET ME AFTER PARTY
 Cipher text: TEMEEMEFAPTRYRAT
 KEY USED: 421635
1 2 3 4 5 6
M E E T M E
A F T E R P
A R T Y
4 2 1 6 3 5
T E M E E M
E F A P T R
Y R A T

13. 13
Every alphabet is shifted with fixed number.
Key: Shift number.
Problem: Only 26 keys to find out.

14. Modern Cryptography
1.Block Ciphers
-encryption of one block of text at a time
-e.g. : Plain text: four and five
Four and five
Key Key Key
wvfa ast wvfa :cipher text

15. 2.Steam Ciphers:
-plaintext is processed one bit at a time
- e.g. : Plain text: Pay 100
Binary of plain text: 010111101 (hypothetical)
Key: 100101011 ----- Perform XOR
____________________
Cipher text 110010110 ----- ZTU9^%D

16. Encryption and Decryption
algorithms
• Data Encryption Standard(DES)
• Advanced Encryption Standard(AES)

17. DES Encryption AES Encryption
DES uses only 56 bits key which provides a
combination of 2^56 = 256 combinations for
encryption.
AES can use 128, 192, 256 bits keys which
provides 2^128, 2^192, 2^256 combinations for
encryption.
DES is restricted to use a Block Size of only 64
bits
AES is restricted to use a Block Size of 128 bits
(double of what is used in DES)
With 64 bits block size, the amount of data that
can be transferred with a single encryption key
is just 32GB.
With AES, it is possible to transfer around 256
billion GB of data. It is probably safe to say that
you can use a single AES encryption key for
any application.
DES encryption is breakable through Brute
Force attack.
AES encryption on the other hand is still not
breakable, though there are some theoretical
discussions about breaking the AES.
DES is an old technique used for
encryption/decryption
AES is relatively new.
Time required to check all the possible keys at
50 billion keys per second – For a 56-bit key:
400 days.
Time required to check all the possible keys at
50 billion keys per second – For a 128-bit key:
5x1021 years (which makes it difficult for the
hackers to decrypt the data)

18. APPLICATIONS
 Defense services
 Secure data manipulation
 E –commerce
 Business transactions
 Internet payment systems
 User identification systems
 Access control
 Data security

19. CONCLUSION
 By using Cryptography techniques
confidentiality, authentication, integrity,
access control and availability of data is
maintained
 Secure Communication is obtained.

20. THANK YOU!