A startup is building a messaging app that requires end-to-end encryption. They need to support group chats with up to 100 participants and allow new members to join without exposing previous messages. Which cryptographic approach best meets these requirements?

Use a public key for each group and have the server hold the private key.

Use a group key that is re-encrypted and distributed to all current members whenever membership changes.

Use a separate symmetric key for each pair of users and relay messages through the server.

Use a single long-lived group key that is shared with all members at the time of group creation.

A software vendor distributes updates to clients. They want clients to verify that the update came from the vendor and was not tampered with during download. Which process should the vendor use?

Encrypt the update with a symmetric key shared with all clients.

Hash the update and publish the hash on the vendor's website.

Sign the update with the vendor's private key and provide the public key to clients for verification.

Encrypt the update with the vendor's public key and provide the private key to clients.

A multinational company uses a hardware security module (HSM) to protect the master key for a database encryption system. The compliance team requires that the master key be rotated every 30 days, but the database contains years of archived data that cannot be re-encrypted quickly. The HSM supports key versioning. What is the most practical approach?

Re-encrypt the entire database with the new key within the 30-day window.

Export the old master key to a software key store and use the new key for all operations.

Keep the same master key but change the key label in the HSM.

Use key versioning: create a new key version for new data, but retain old versions to decrypt archived data.

A company's compliance policy requires that all encryption keys be backed up and recoverable in case of data loss. However, the security team is concerned that a backup of the private key could be stolen. Which backup strategy provides both recoverability and security?

Store a plain-text copy of the key in a safety deposit box.

Encrypt the key with a password and store the encrypted key in the same backup server.

Split the key into multiple shares using secret sharing and store each share in a different secure location.

Store the key in a public cloud storage with a shared access link.

Which of the following is a characteristic of symmetric cryptography?

Provides non-repudiation by default

Requires a key exchange protocol like Diffie-Hellman

Uses a public key for encryption and a private key for decryption

Uses the same key for encryption and decryption

EC-CouncilBlockchain Developer Certification

Domain 2Objective 1

Cryptographic Principles BDC Practice Questions (Page 7)

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

37questions here

8free pages

6concepts

Questions 31–35

31expert · hard
A startup is building a messaging app that requires end-to-end encryption. They need to support group chats with up to 100 participants and allow new members to join without exposing previous messages. Which cryptographic approach best meets these requirements?
Select an answer first
32application · medium
A software vendor distributes updates to clients. They want clients to verify that the update came from the vendor and was not tampered with during download. Which process should the vendor use?
Select an answer first
33expert · hard
A multinational company uses a hardware security module (HSM) to protect the master key for a database encryption system. The compliance team requires that the master key be rotated every 30 days, but the database contains years of archived data that cannot be re-encrypted quickly. The HSM supports key versioning. What is the most practical approach?
Select an answer first
34expert · hard
A company's compliance policy requires that all encryption keys be backed up and recoverable in case of data loss. However, the security team is concerned that a backup of the private key could be stolen. Which backup strategy provides both recoverability and security?
Select an answer first
35foundation · easy
Which of the following is a characteristic of symmetric cryptography?
Select an answer first

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