A developer is implementing a smart contract that requires a random number for a lottery. The contract must be fair and unpredictable, and the developer wants to avoid a single point of failure. Which approach is most robust?

Use the block hash of the current block

Use a centralized oracle service

Use a timestamp of the transaction

Use a commit-reveal scheme where multiple parties commit to secrets and the final random value is derived from all revealed secrets

A developer is designing a blockchain-based supply chain where each product has a unique identifier. The system must allow any participant to verify the authenticity of a product without revealing the entire supply chain history. Which mechanism is most suitable?

Zero-knowledge proofs that a product's identifier is in the set of valid products

Using a digital signature from the manufacturer on each product

Encrypting the product identifier with a shared key

Storing the full supply chain history in plaintext on-chain

A financial consortium needs to share encrypted transaction data among members, but they also want to allow a regulator to compute the total value of transactions over a period without decrypting each transaction. Which cryptographic mechanism should be used?

A digital signature over each transaction, with the regulator verifying the signatures.

A zero-knowledge proof of the total value, generated by each member.

A hash of each transaction, with the regulator comparing hashes.

Fully homomorphic encryption (FHE) on the transaction amounts.

A blockchain-based notary service needs to prove that a document existed at a certain time without revealing the document's contents. The service plans to store a hash on-chain. Which additional mechanism should be used to provide a tamper-evident timestamp?

Use a zero-knowledge proof to prove the document's existence without revealing it.

Use a digital signature from a trusted third party over the hash and current time.

Include the hash in a transaction that is included in a block, relying on the block's timestamp.

Encrypt the document and store the ciphertext on-chain.

A developer is building a blockchain-based notary service. Users submit documents, and the service stores a hash of each document on-chain. Later, a user claims that a document was submitted on a specific date. What should the service provide to the user to prove this claim?

The encrypted document and the decryption key

The private key used to sign the transaction

The original document and the on-chain hash with its timestamp

EC-CouncilBlockchain Developer Certification

Domain 2Objective 5

Advanced Cryptographic Mechanisms BDC Practice Questions (Page 6)

Part of the Cryptography and Security Foundations domain, which makes up ~10% of our current practice bank.

31questions here

7free pages

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Questions 26–30

26expert · hard
A developer is implementing a smart contract that requires a random number for a lottery. The contract must be fair and unpredictable, and the developer wants to avoid a single point of failure. Which approach is most robust?
Select an answer first
27application · hard
A developer is designing a blockchain-based supply chain where each product has a unique identifier. The system must allow any participant to verify the authenticity of a product without revealing the entire supply chain history. Which mechanism is most suitable?
Select an answer first
28application · medium
A financial consortium needs to share encrypted transaction data among members, but they also want to allow a regulator to compute the total value of transactions over a period without decrypting each transaction. Which cryptographic mechanism should be used?
Select an answer first
29application · medium
A blockchain-based notary service needs to prove that a document existed at a certain time without revealing the document's contents. The service plans to store a hash on-chain. Which additional mechanism should be used to provide a tamper-evident timestamp?
Select an answer first
30application · medium
A developer is building a blockchain-based notary service. Users submit documents, and the service stores a hash of each document on-chain. Later, a user claims that a document was submitted on a specific date. What should the service provide to the user to prove this claim?
Select an answer first

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