Cryptocurrency Core Cryptographic Principles 3

Question 1

What is 'perfect forward secrecy' (PFS) in cryptographic key exchange?

Accepted Answer

Each session uses a new key so past sessions remain secure even if a long-term key is compromised

Answer

PFS ensures that compromise of a long-term private key does not expose past session keys, protecting historical communications.

Question 2

Which of the following best describes the Diffie-Hellman key exchange?

Accepted Answer

Two parties derive a shared secret over a public channel without transmitting it directly

Answer

Diffie-Hellman allows two parties to establish a shared secret over an insecure channel without ever transmitting the secret itself.

Question 3

What does 'salting' a password hash accomplish?

Accepted Answer

It prevents two identical passwords from producing the same hash and defeats precomputed rainbow tables

Answer

A salt is random data added to a password before hashing, ensuring identical passwords produce different hashes and defeating rainbow table attacks.

Question 4

Which attack exploits the reuse of a one-time pad or stream cipher keystream?

Accepted Answer

Crib-dragging attack

Answer

Crib-dragging exploits keystream reuse in stream ciphers or OTPs by XORing two ciphertexts and guessing known plaintext segments.

Question 5

In asymmetric cryptography, what is the relationship between key length and security level?

Accepted Answer

RSA keys must be much longer than symmetric keys to achieve equivalent security

Answer

RSA requires ~3072-bit keys to match the security of 128-bit AES because factoring is easier than brute-forcing a symmetric key of the same length.

Cryptocurrency Practice Test