Core Cryptographic Principles Flashcards

Which property ensures that a hash function output cannot be used to determine the original input?

Answer: Pre-image resistance

Pre-image resistance means it is computationally infeasible to reverse a hash and find the original input.

What is the purpose of a nonce in cryptographic protocols?

Answer: To ensure a value is used only once, preventing replay attacks

A nonce (number used once) prevents replay attacks by ensuring each transaction or message is unique.

In elliptic curve cryptography (ECC), what operation is considered the 'hard problem' that provides security?

Answer: Elliptic curve discrete logarithm problem

ECC security relies on the difficulty of the elliptic curve discrete logarithm problem — deriving the scalar from a point multiplication.

What distinguishes a MAC (Message Authentication Code) from a digital signature?

Answer: MACs require a shared secret key; signatures use a public/private key pair

MACs authenticate messages using a shared secret, while digital signatures use asymmetric key pairs and provide non-repudiation.

Which block cipher mode of operation converts a block cipher into a stream cipher?

Answer: CTR (Counter Mode)

CTR mode generates a keystream by encrypting successive counter values, effectively turning a block cipher into a stream cipher.

What is the 'birthday paradox' relevant to in cryptographic hash functions?

Answer: It helps estimate the probability of finding two inputs with the same hash

The birthday paradox shows that collisions in a hash function can be found much faster than expected — roughly after 2^(n/2) attempts for an n-bit hash.

In the context of Bitcoin, what cryptographic curve is used to generate key pairs?

Answer: secp256k1

Bitcoin uses the secp256k1 elliptic curve, chosen by Satoshi Nakamoto for its specific mathematical properties.