Cryptography and Network Security Chapter 9

Questions and Answers

What is the primary characteristic of private-key cryptography?

It uses a pair of keys for encryption and decryption.

It guarantees authenticity through digital signatures.

It requires a public key known by everyone for encryption.

It employs a single shared key between sender and receiver. (correct)

What major problem does public-key cryptography address?

The requirement for symmetric keys in communication.

The challenge of key distribution without a trusted KDC. (correct)

The limited number of keys that can be generated.

The need for fast encryption and decryption processes.

In public-key cryptography, what is true of the private key?

It is the same as the public key.

It can be derived from the public key easily.

It must be shared between all parties.

It is known only to the recipient. (correct)

Which of the following describes one of the requirements for public-key algorithms?

It must be computationally infeasible to find the decryption key from the encryption key. Signup and view all the answers

What is one of the common applications of public-key cryptography?

Both encryption and digital signatures. Signup and view all the answers

What makes public-key cryptography asymmetric?

The keys used for encrypting and decrypting are different. Signup and view all the answers

Who are credited with the public invention of public-key cryptography?

Whitfield Diffie and Martin Hellman. Signup and view all the answers

What is a key requirement of a trapdoor one-way function in public-key cryptography?

It makes it difficult to determine the input from the output. Signup and view all the answers

Study Notes

Private-Key Cryptography

Traditional cryptography utilizes a single key shared between sender and receiver, known as private or secret key cryptography.
If this shared key is disclosed, the security of the communication is compromised.
This method is symmetric, meaning both parties hold equal status, but does not protect the sender from forgery claims by the receiver.

Public-Key Cryptography

Considered a monumental advancement in the 3000-year evolution of cryptography.
Utilizes two distinct keys: a public key available to anyone and a private key known only to the recipient.
This approach is asymmetric; parties do not hold equal power in the process.
It employs number theoretic concepts, complementing rather than replacing symmetric key cryptography.

Reasons for Public-Key Cryptography

Developed to resolve issues related to key distribution, avoiding reliance on a Key Distribution Center (KDC) for secure communication.
Facilitates digital signatures, which authenticate that a message originates from the claimed sender.
Public invention credited to Whitfield Diffie and Martin Hellman in 1976, although earlier known in classified circles.

Key Components of Public-Key Cryptography

The public key can encrypt messages and verify digital signatures, while the private key is used to decrypt messages and create signatures.
It is computationally infeasible to derive the private key from the public key, ensuring security.
Asymmetric nature means those who encrypt or verify cannot simultaneously decrypt or sign.

Public-Key Applications

Public-Key systems can be categorized into three primary applications:
- Encryption/Decryption for ensuring message secrecy.
- Digital Signatures for guaranteeing message authenticity.
- Key Exchange for secure session keys.
Some algorithms serve multiple uses, while others are specialized for a single function.

Public-Key Requirements

Effective Public-Key algorithms depend on two critical requirements:
- It must be computationally infeasible to discover the decryption key with only knowledge of the algorithm and encryption key.
- It should be computationally straightforward to encrypt or decrypt messages when the corresponding key is available.
In some algorithms, either key may serve for encryption, the other must decrypt.
Necessitates a trapdoor one-way function to ensure secure operations.

Description

Explore the principles of private-key and public-key cryptography in Chapter 9 of Cryptography and Network Security. Understand how symmetric key systems work, their vulnerabilities, and the groundbreaking advancements introduced by asymmetric cryptography. Test your knowledge on these fundamental concepts and their applications in secure communications.