Public Key Recap

Question 1

How do Public Keys perform en/decryption?

Answer 1

Through a key pair. One is used for encryption and the opposite is used for decryption.

Question 2

Which of the two keys is shared?

Answer 2

The Public Key

Question 3

What is the disadvantage of Public Key encryption?

Answer 3

Too slow for real-time communications.

Question 4

What are the two main applications of public key encryption?

Answer 4

Identity checking and key protection

Question 5

What does RSA leverage as a difficulty factor?

Answer 5

It produces large prime numbers.

Question 6

What does homomorphic encryption allow?

Answer 6

Performing mathematical operations on ciphered values.

Question 7

Why is RSA not well-suited for embedded systems?

Answer 7

Because of the heavy overhead on processors.

Question 8

What is and improved solution to RSA?

Answer 8

Elliptic Curve

Question 9

What is Elliptic Curve often used for?

Answer 9

Key exchange methods (i.e. Elliptic Curve Diffie Hellman (ECDH)) and digital signatures (i.e. Elliptic Curve Digital Signature Algorithm (ECDSA))

Question 10

What are the main advantages of Elliptic Curve methods?

Answer 10

Small keys (the prime number is typically 160-bits).
The creation of curves is difficult to crack.
Can factor values.

Question 11

What type of cryptography does Bitcoin use?

Answer 11

Elliptic Curve Cryptography

Question 12

What is El Gamal?

Answer 12

A public key method that is used for encryption and digital signatures. It uses discrete logarithms.

Question 13

What is Cramer-Shoup?

Answer 13

Public key encryption. An extension of El Gamal that adds one-way hashing to prevent adaptive chosen ciphertext attacks.

Question 14

What does Paillier Cryptosystem support?

Answer 14

Homomorphic encryption.

Question 15

What are the four steps to send a digitally signed message using public key cryptology?

Answer 15

Sender signs a message with sender’s private key.
Sender encrypts message with receiver’s public key.
Receiver decrypts message with receiver’s private key.
Revceiver verifies message with sender’s public key.

Question 16

What are the five steps to send a hashed message?

Answer 16

Sender produces a message hash and encrypts it using the sender’s private key.
Sender encrypts original message and encrypted hash with the receiver’s public key.
Receiver decrypts with receiver’s private key.
Receiver decrypts original hash with sender’s public key.
Reveiver computes hash of the original message and compares it to the original hash for authenticity.