Advanced Cryptographic Mechanisms in Blockchain Security BBLC Practice Questions (Page 7)

Questions 31–35

1. 31expert · hard

   A blockchain network currently uses ECC-256 for signatures. A quantum threat assessment indicates that within 5 years, quantum computers could break ECC. The network must migrate to post-quantum signatures, but the migration must not disrupt existing users or require them to change their private keys immediately. Which migration strategy best balances security and usability?

   • AAdopt a hybrid signature scheme that combines ECC and a post-quantum algorithm, allowing gradual transition.
   • BIncrease ECC key size to 512 bits and continue using ECC.
   • CImmediately require all users to generate new post-quantum key pairs and abandon ECC.
   • DSwitch to RSA-4096 as an interim measure.
   Reveal Solution Discussion Select an answer first
2. 32application · medium

   A privacy-focused blockchain wants to allow users to prove they are over 18 without revealing their exact birth date or any other personal data. Which cryptographic technique enables this?

   • AHash of the birth date
   • BSymmetric encryption of the birth date
   • CDigital signature over the birth date
   • DZero-knowledge proof
   Reveal Solution Discussion Select an answer first
4. 33expert · hard

   A blockchain platform needs to allow users to prove that a set of transactions are included in a block without revealing the other transactions. They also need to minimize the amount of data transferred to the user. Which mechanism should they use?

   • AUse a digital signature over the block hash.
   • BSend the entire block to the user.
   • CUse homomorphic encryption to hide other transactions.
   • DMerkle proofs for each transaction, using the block's Merkle root.
   Reveal Solution Discussion Select an answer first
5. 34expert · hard

   A regulatory body requires a blockchain to prove that all transactions comply with a rule (e.g., no transaction exceeds $1,000) without revealing transaction amounts. The blockchain must also allow auditors to verify compliance for any transaction. Which approach should be used?

   • AUse zero-knowledge range proofs to show each transaction amount is within the allowed range without revealing the exact amount.
   • BUse digital signatures from a trusted third party to attest compliance.
   • CEncrypt all transaction amounts with homomorphic encryption and allow auditors to decrypt them.
   • DPublish a hash of each transaction amount.
   Reveal Solution Discussion Select an answer first
6. 35expert · hard

   A blockchain platform is evaluating ECC vs. RSA for digital signatures. They need to minimize the size of signatures stored on-chain while maintaining a security level equivalent to AES-128. Which algorithm and key size should they choose?

   • ARSA with a 2048-bit key, producing signatures of 2048 bits.
   • BRSA with a 3072-bit key, producing signatures of 3072 bits.
   • CECC with a 512-bit key, producing signatures of 1024 bits.
   • DECC with a 256-bit key, producing signatures of about 512 bits.
   Reveal Solution Discussion Select an answer first