Free Certified Blockchain Professional (CBCP) Cryptography and Hashing Questions and Answers

Question 1

A blockchain network relies on asymmetric cryptography for securing transactions. Which of the following accurately describes the process of creating a valid digital signature for a new transaction?

Accepted Answer

A hash of the transaction data is generated, and this hash is then encrypted with the sender's private key.

Answer

A digital signature in a blockchain context is created by first hashing the transaction data to create a unique, fixed-size digest. This digest is then encrypted using the sender's private key. This process ensures authenticity, integrity, and non-repudiation, as only the holder of the private key could have created the signature, and any alteration to the transaction data would result in a different hash.

Question 2

In a Proof-of-Work (PoW) blockchain like Bitcoin, what is the primary function of a 'nonce'?

Accepted Answer

A variable that miners repeatedly change in the block header to find a hash value below a specific target.

Answer

The nonce (number used once) is a critical component of the mining process in PoW blockchains. Miners iterate through different nonce values, hashing the block header each time, until they find a hash that meets the network's difficulty target (e.g., starts with a certain number of zeros). This trial-and-error process is the 'work' in Proof-of-Work.

Question 3

Which cryptographic property of a hash function ensures that it is computationally infeasible to find two different inputs that produce the exact same hash output?

Accepted Answer

Collision Resistance

Answer

Collision resistance is the property that makes it computationally infeasible to find any two distinct inputs, x and y, such that H(x) = H(y). This is crucial for blockchain integrity, as it prevents an attacker from creating a fraudulent transaction that has the same hash as a legitimate one.

Question 4

A financial institution is designing a private blockchain. They need to encrypt large volumes of transactional data for storage within the blocks. While asymmetric cryptography is used for signing transactions, which cryptographic method would be most efficient for encrypting the bulk data itself?

Accepted Answer

Symmetric cryptography using a shared secret key.

Answer

Symmetric cryptography uses a single key for both encryption and decryption, making it significantly faster and more computationally efficient than asymmetric cryptography, especially for large amounts of data. While asymmetric cryptography is ideal for key exchange and digital signatures, symmetric encryption is better suited for bulk data encryption.

Question 5

If a malicious actor manages to find a second, different transaction that produces the same hash as a victim's original, signed transaction, which specific cryptographic security property has been broken?

Accepted Answer

Second Preimage Resistance

Answer

Second preimage resistance (or weak collision resistance) is the property where, given a specific input 'x', it is computationally infeasible to find a different input 'x'' such that H(x) = H(x'). Breaking this would allow an attacker to forge a digital signature by creating a malicious document that hashes to the same value as a legitimate one the user has already signed.

CBCP - Certified Blockchain Professional Practice Test

CBCP - Certified Blockchain Professional Practice Test

Free Certified Blockchain Professional (CBCP) Cryptography and Hashing Questions and Answers