The document discusses cryptography, detailing encryption and decryption processes, along with techniques like symmetric and asymmetric key algorithms. It highlights the DES algorithm and the role of public-key cryptography, explaining key generation and the concepts of public and private keys. Additionally, it explores the application of cryptography in Bitcoin, emphasizing its unique properties and the underlying technology, the blockchain.

1. CRYPTOGRAPHY
Submitted by: Smruti Ranjan Sahoo
Underguidance by: Prof.Puspanjali Mohapatra

3. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C

4. Data encryption and Decryption
Encryption – The process of converting plain text message
into unintelligible format in known as encryption .

5. Decryption : The process of converting
unreadable message i.e cipher text into
plain text is called data decryption.

6. There are two types of technique used for
encryption i.e
1.Substitution :
In this we substitute each character to any other character or
number or special character .
1.Transposition :
In this we substitute each character to any
other character and change the position of character .

7. Symmetric key Cryptography
In this we use only one key for both
encryption and decryption of data.
There are various algorithms such as DES,
Triple
DES,RC4,RC5,Blowfish,Twofish….etc.

8. DES Algorithm

9. How DES works ??
56-bit 56-bit
key key
Block 1 Block 2
64 bit plain
text
DES
64 bit cipher
text
64-bit plain
text
DES
64-bit cipher
text

10. Key generation of DES

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

11. Steps involved in DES algorithm

12. Initial Permutation(IP)
Division into 32-bit blocks:
58 50 42 34 28 18 10 2 60 52 44 36 28 20 12 4
62 54 46 38 30 22 14 6 64 56 48 40 32 24 16 8
57 49 41 33 25 17 9 1 59 51 43 35 27 19 11 3
61 53 45 37 29 21 13 5 63 55 47 39 31 23 15 1

13. Expansion Function:
The 32 bit block are expand into 48 bit block . The table is called “Expansion Table”.

14. S-box Substitution
48-bit input block
6-bit sub block 6-bit sub block
6-bit sub block
S-box 1 S-box 2 S-box 8
4-bit output 4-bit output 4-bit output
32-bit output block

16. P-box permutation:
Final Permutation:
16 7 20 21 29 12 28 17 1 15 23 26 5 18 31 10
2 8 24 14 32 27 3 9 19 13 30 6 22 11 4 25

17. Asymmetric Key Algorithm
Public-key cryptography, also known as asymmetric cryptography, is a class of
cryptographic algorithms which requires two separate keys, one of which is secret (or
private) and one of which is public. Although different, the two parts of this key pair are
mathematically linked.

18. Diagram of Asymmetric key
cryptography

19. 

20. Five Basic steps for calculation :
Large Prime Number Generation: Two large
prime numbers p and q need to be generated.
These numbers are very large: At least 512 digits,
but 1024 digits is considered safe.
Modulus: From the two large numbers, a
modulus n is generated by multiplying p and q.
Totient: The totient of n,ϕ(n) is calculated.

21.  Public Key: A prime number is calculated from
the range [3,ϕ(n)) that has a greatest common
divisor of 1 with ϕ(n).
 Private Key: Because the prime in step 4 has a
gcd of 1 with ϕ(n), we are able to determine it's
inverse with respect to mod ϕ(n).

22. There are various application of cryptography in our day to day life .
One of is “BitCoin”
 Bitcoin uses peer-to-peer technology to operate with no central
authority or banks; managing transactions and the issuing of
bitcoins is carried out collectively by the network.
 Bitcoin is open-source; its design is public, nobody owns or
controls Bitcoin and everyone can take part.
 Through many of its unique properties, Bitcoin allows exciting
uses that could not be covered by any previous payment system.
 Bitcoin is a form of digital currency, created and held
electronically. No one controls it. Bitcoins aren’t printed, like
dollars or euros – they’re produced by people, and increasingly
businesses, running computers all around the world, using
software that solves mathematical problems.

23. How does Bitcoin work?
 From a user perspective, Bitcoin is nothing more than a mobile app or
computer program that provides a personal Bitcoin wallet and enables a
user to send and receive bitcoins.
 Behind the scenes, the Bitcoin network is sharing a massive public ledger
called the "block chain". This ledger contains every transaction ever
processed which enables a user's computer to verify the validity of each
transaction. The authenticity of each transaction is protected by digital
signatures corresponding to the sending addresses therefore allowing all
users to have full control over sending bitcoins.
 Thus, there is no fraud, no chargebacks and no identifying information that
could be compromised resulting in identity theft. To learn more about
Bitcoin, you can consult the original Bitcoin whitepaper, read through the
extremely thorough Frequently Asked Questions, listen to a Bitcoin
podcast or read the latest Bitcoin news.

24. THANK YOU