Cryptographic Principles BDC Practice Questions (Page 3)

Questions 11–15

1. 11application · medium

   A government agency requires that all outgoing official documents be verifiable by any citizen without prior registration. The agency also needs to ensure that the documents have not been altered. What should the agency implement?

   • AEncrypt each document with the agency's public key and publish the private key.
   • BPublish a hash of each document on the agency's website.
   • CUse a symmetric key to encrypt each document and share the key only with registered citizens.
   • DDigitally sign each document with the agency's private key and publish the public key.
   Reveal Solution Discussion Select an answer first
2. 12application · medium

   A mobile app needs to encrypt user data locally on the device. The app does not have access to a server for key exchange. Which key management approach is most appropriate?

   • AGenerate a symmetric key on the device and protect it with a key derived from the user's passphrase.
   • BUse a hard-coded symmetric key embedded in the app binary.
   • CUse the device's public key to encrypt the data and store the private key in the app's shared preferences.
   • DUse a symmetric key generated once and stored in a plain text file on the device.
   Reveal Solution Discussion Select an answer first
4. 13expert · hard

   A company is designing a key management system for a large number of IoT devices. Each device needs to encrypt data before sending it to the cloud. The devices have limited computational power and storage. Which key management approach is most appropriate?

   • AUse a single symmetric key shared across all devices.
   • BUse a symmetric key pre-provisioned on each device and rotate it periodically via a secure channel.
   • CUse a public key infrastructure (PKI) with certificates for each device.
   • DUse asymmetric encryption with a unique key pair per device, stored in the device's secure element.
   Reveal Solution Discussion Select an answer first
5. 14application · medium

   A blockchain network uses a digital signature scheme for transaction authorization. An attacker has been observed measuring the power consumption of a validator's hardware during signing operations. Which type of attack is this, and what is the most effective mitigation?

   • ABrute-force attack; use a stronger hash function.
   • BSide-channel attack; use constant-time signing algorithms and hardware shields.
   • CReplay attack; add a nonce to the signing process.
   • DMan-in-the-middle attack; use a longer key length.
   Reveal Solution Discussion Select an answer first
6. 15expert · hard

   A security architect is designing a password storage system for a high-security application. The system must resist both brute-force attacks on fast hardware and precomputation (rainbow table) attacks. Which approach best meets both requirements?

   • AUse a symmetric encryption algorithm to store passwords and keep the key in the application code.
   • BUse a fast hash function with a long random salt per user.
   • CUse SHA-256 with a global static salt.
   • DUse a slow, memory-hard hash function (e.g., Argon2) with a unique salt per user.
   Reveal Solution Discussion Select an answer first