Cryptocurrency Core Cryptographic Principles 5

Question 1

What is a 'padding oracle attack' and which cipher mode is most vulnerable to it?

Accepted Answer

An attack that exploits error messages about invalid padding in CBC mode to decrypt ciphertext

Answer

In a padding oracle attack, an attacker queries a system that reveals whether decrypted padding is valid, allowing CBC-mode ciphertext to be decrypted block-by-block.

Question 2

In the context of digital signatures, what does 'non-repudiation' mean?

Accepted Answer

The signer cannot later deny having signed the message because only they hold the private key

Answer

Non-repudiation means the signer cannot plausibly deny signing a message, since only the holder of the private key could have produced the valid signature.

Question 3

Which of the following is a post-quantum cryptographic algorithm standardized by NIST in 2024?

Accepted Answer

CRYSTALS-Kyber (ML-KEM)

Answer

CRYSTALS-Kyber, standardized as ML-KEM by NIST in 2024, is a lattice-based key encapsulation mechanism designed to resist quantum computer attacks.

Question 4

What is 'key stretching' and which algorithms are commonly used for it?

Accepted Answer

Deliberately slowing down hash computation to make brute-force attacks more expensive; used in bcrypt, scrypt, and Argon2

Answer

Key stretching algorithms like bcrypt, scrypt, and Argon2 apply thousands of hash iterations and memory requirements to make password cracking computationally expensive.

Question 5

What is the primary cryptographic purpose of a Merkle tree in Bitcoin?

Accepted Answer

To efficiently verify that a specific transaction is included in a block without downloading all transactions

Answer

Merkle trees allow Simplified Payment Verification (SPV) clients to verify transaction inclusion by checking a logarithmic-length proof path rather than all transactions.

Cryptocurrency Practice Test

Cryptocurrency Practice Test

Cryptocurrency Core Cryptographic Principles 5