Free Certified Blockchain Professional (CBCP) Cryptography and Hashing Questions and Answers — 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?
- The transaction data is encrypted using the sender's public key, and the resulting ciphertext is the digital signature.
- A hash of the transaction data is generated, and this hash is then encrypted with the sender's private key. (Correct answer)
- The entire block's data, including the transaction, is hashed, and the hash is encrypted with the network's master private key.
- The sender's public key is hashed and then encrypted using a symmetric key shared with the recipient.
Correct answer: A hash of the transaction data is generated, and this hash is then encrypted with the sender's private key.
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'?
- To encrypt the transaction data within a block for confidentiality.
- It is a counter for the number of transactions sent from a specific address, preventing replay attacks.
- A variable that miners repeatedly change in the block header to find a hash value below a specific target. (Correct answer)
- The public key of the miner who successfully solves the cryptographic puzzle.
Correct answer: A variable that miners repeatedly change in the block header to find a hash value below a specific target.
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?
- Preimage Resistance
- Second Preimage Resistance
- Collision Resistance (Correct answer)
- Deterministic Output
Correct answer: Collision Resistance
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?
- Hashing algorithms like SHA-256.
- Asymmetric cryptography using the public key of all network participants.
- Symmetric cryptography using a shared secret key. (Correct answer)
- Steganography to hide the data within other block components.
Correct answer: Symmetric cryptography using a shared secret key.
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?
- Collision Resistance
- Preimage Resistance
- Second Preimage Resistance (Correct answer)
- Avalanche Effect
Correct answer: Second Preimage Resistance
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.
Question 6: Which of the following best describes the 'avalanche effect' as it relates to cryptographic hash functions used in blockchain?
- The computational difficulty of finding a valid nonce increases exponentially over time.
- A small change in the input data (e.g., altering a single character in a transaction) results in a drastically different and unpredictable hash output. (Correct answer)
- Multiple transactions are bundled together and hashed, creating a cascade of linked data.
- The process of using the previous block's hash as an input for the current block's hash, creating a chain reaction.
Correct answer: A small change in the input data (e.g., altering a single character in a transaction) results in a drastically different and unpredictable hash output.
The avalanche effect is a desirable property of cryptographic hash functions where a minor change to the input (like flipping a single bit) produces a significantly different output hash. This ensures that it's impossible to predict how to change the input to achieve a desired output, which is fundamental to making the blockchain tamper-evident.
Free Certified Blockchain Professional (CBCP) Cryptography and Hashing Questions and Answers
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?