1. Public Key Encryption and the RSA Algorithm
Computer Networking- A top-Down Approach Featuring the Internet
James F Kurose and Keith W Ross, Second Edition, Pearson Publication
Chapter 7- page 642 – 647

2. Goal
To understand what public key encryption is doing to achieve security.
To focus on the working principle of public key encryption using RSA algorithm

3. Objective
The student will be able to apply the technique followed in public key encryption method

4. Private-Key Cryptography
traditional private/secret/single key cryptography uses only one key .
Key is shared by both sender and receiver and needs to be known in advance.
if the key is disclosed communications are compromised.
This is also referred to as symmetric key approach.

5. Possibility of secret key in advance
In internet communicating parties never meet or converse except over the network.
Is it possible for communication to take place without having secret key in advance?
Answer is YES.

6. Public-Key Cryptography
uses two keys – a public key and a private key
asymmetric since sender do not know private key of receiver
uses clever application of number theory concepts to function
complements rather than replaces private key cryptography

7. Diagram to understand PKE

8. Public Key Encryption
public-key/two-key/asymmetric cryptography involves the use of two keys:
a public-key, which may be known by anybody, and can be used to encrypt messages
a private-key, known only to the recipient, used to decrypt messages
is asymmetric because
those who encrypt messages cannot decrypt messages

9. Bob communicating with Alice

10. Why PK Cryptography? developed to address two key issues:
key distribution – how to have secure communications in general without having to trust a KDC with your key
digital signatures – how to verify a message comes intact from the claimed sender
public key invention is due to Whitfield Diffie & Martin Hellman at Stanford U. in 1976

11. Applications can classify uses into 3 categories:
encryption/decryption (provide secrecy)
digital signatures (provide authentication)
key exchange (of session keys)

12. RSA Ron Rivest, Adi Shamir & Leonard Adleman of MIT in 1977.
best known & widely used public-key scheme

13. Two interrelated components of RSA
The choice of the public key and the private key
The encryption and decryption algorithm

14. Steps to generate public and private Keys
Choose two large prime numbers, p and q.
Compute n = pq and z = (p – 1)(q – 1).
3. Choose a number, e, less than n, that has no common factors (other than 1) with z.
4. Find a number, d, such that ed – 1 is exactly divisible (that is, with no remainder) by z. We choose d such that ed mod z = 1
5. The public key that Bob makes available to the world, KB+, is the pair of numbers (n, e); his private key, KB–, is the pair of numbers (n, d).

15. Encryption and Decryption steps

16. Pros and Cons of RSA
The security of RSA relies on the fact that there are no known algorithms for
quickly factoring a number, in this case the public value n, into the primes p and q.
It is not known whether or not there exist fast algorithms for factoring a number, hence the security of RSA is not guaranteed.
If one knew p and q, then given the public value e, one could easily compute the secret key, d.

17. Things to ponder The application of PKC
Limitation of Public key cryptography
KDC
Digital signature
Example to solve with integer numbers
Example to solve with text
Alert points

18. General Instruction for evaluation
Students will follow the team members formed for problem solving
Each team will be assigned a task on the spot in the classroom based on this ppt.

19. End of RSA FLIPPED CLASSROOM SESSION
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