Diffie-Hellman Key Exchange Quiz

10 Questions

What is the key used in symmetric encryption called?

Secret key

What is the relationship between the sender and receiver in public-key cryptography?

They use different keys

Which of the following is not a common application of public-key cryptography?

Authentication

What is the main purpose of using public-key cryptography for digital signatures?

To provide authentication

Which of the following algorithms is an example of a public-key cryptography algorithm?

RSA

What is the primary difference between symmetric and asymmetric cryptography?

The parties involved in the communication

What is the purpose of using public-key cryptography for key exchange?

To establish a session key

Which of the following statements about symmetric and asymmetric cryptography is true?

Symmetric cryptography uses a single key for both encryption and decryption, while asymmetric cryptography uses a pair of keys

What is the primary advantage of using public-key cryptography over symmetric cryptography?

Easier key management

Which of the following statements about the DES and RSA algorithms is correct?

DES is a symmetric algorithm, while RSA is an asymmetric algorithm

Study Notes

Diffie-Hellman Key Exchange

Diffie-Hellman (DH) key exchange technique was first defined in 1976 by Diffie and Hellman.
DH key exchange is a method of exchanging public information to obtain a shared secret.
DH is not an encryption algorithm.
DH key exchange has three important properties:
- The resulting shared secret cannot be computed by either of the parties without the cooperation of the other.
- A third party observing all the messages transmitted during DH key exchange cannot deduce the resulting shared secret.
- The shared secret is symmetric, meaning both parties have the same key.

Diffie-Hellman Key Exchange Process

System parameters are public and include a large prime number p and a primitive root g.
Alice and Bob exchange public keys, each computed using their private random values and the system parameters.
Alice and Bob calculate the shared secret key using their private random values and the public keys exchanged.

Diffie-Hellman Mathematical Analysis

Alice and Bob agree on public parameters p and g.
Alice generates a private random value a and computes a public key ga mod p.
Bob generates a private random value b and computes a public key gb mod p.
Alice and Bob exchange public keys and compute the shared secret key.

Man-in-the-Middle Attack

An attacker, Fred, can intercept public keys and compute a fake public key.
Alice and Bob will compute a shared secret key with the attacker, but not with each other.

Public Key Cryptography

Public-key cryptography is a radical departure from symmetric cryptography.
Each user has a public key and a private key.
Public-key cryptography provides confidentiality, authentication, and key distribution.

Properties of Public Key Cryptography

The encryption key is not the same as the decryption key.
Public-key cryptography is asymmetric, using two separate keys.
Public-key cryptography provides a solution to key distribution and authentication problems.

History of Public Key Cryptography

1976: Diffie and Hellman published an article on public-key cryptography and introduced the concept of key exchange.
1977: Rivest, Shamir, and Adleman invented the RSA scheme.
Later: Many other public-key cryptography methods were developed, including El Gamal, DSS, and DH.

Symmetric vs Public-Key Cryptography

Symmetric cryptography uses the same algorithm with the same key for encryption and decryption.
Public-key cryptography uses a pair of keys, one for encryption and one for decryption.
Symmetric cryptography is also known as private-key cryptography, while public-key cryptography is asymmetric.

Applications of Public-Key Cryptosystems

Encryption/decryption: using the recipient's public key to encrypt a message.
Digital signature: using the sender's private key to sign a message.
Key exchange: exchanging a session key between two parties.