A Java web service uses RSA-OAEP for encrypting sensitive payloads. When decryption fails, the service returns an HTTP 400 with a message that distinguishes 'Invalid ciphertext' from 'Invalid padding'. An attacker exploits this to recover the plaintext. What is the primary defensive coding fix?

Return a generic 400 error for all decryption failures and log the specific cause server-side.

Return the stack trace to help the client understand the failure.

Add a delay before returning the error to slow down the attacker.

Use a different padding scheme like PKCS#1 v1.5 to avoid the oracle.

A security team is reviewing a Java codebase for cryptographic weaknesses. They want to identify hardcoded keys, weak algorithms, and improper random number generation. Which testing approach would be most effective for this task?

Review the code manually without any automated tools.

Run a static analysis tool with rules for cryptographic API misuse and secret detection.

Use a network packet analyzer to capture encrypted traffic and analyze the cipher suites.

Perform only dynamic black-box penetration testing against the running application.

A Java application accepts a hex-encoded IV from the client and uses it to decrypt data with AES-CBC. An attacker modifies the IV to alter the first block of plaintext. The application does not validate the IV length or format. Which defensive coding change is most effective?

Validate that the IV is exactly the block size (16 bytes) and use a MAC to authenticate the ciphertext and IV.

Allow any IV length and rely on the decryption to fail if it is wrong.

Use the client-supplied IV as the encryption key.

Ignore the IV and use a hard-coded IV.

A security team is testing a Java application that uses AES-CBC with PKCS#5 padding for encryption. They notice that the application returns different HTTP status codes for 'padding error' versus 'MAC mismatch'. They want to confirm whether the application is vulnerable to a padding oracle attack. Which testing approach would most conclusively demonstrate the vulnerability?

Send a series of modified ciphertexts and observe whether the response consistently distinguishes padding errors from other failures.

Run a static analysis tool to check for the use of AES-CBC.

Review the source code to see if the padding is implemented correctly.

Check the server logs for decryption errors.

Which of the following is a secure way to generate a cryptographic key in Java?

Use `System.currentTimeMillis()` as the key

Use `new SecureRandom()` and `nextBytes()` to generate key material

Use `Math.random()` to generate key bytes

Use `Random` class with a fixed seed

EC-CouncilCertified Application Security Engineer (Java)

Domain 5Objective 3

Cryptographic Attacks and Defensive Coding CASEJAVA Practice Questions (Page 3)

Part of the Secure Coding: Cryptography domain, which makes up ~13% of our current practice bank. EC-Council does not publish an official question count, but from its 120-minute exam (~50–80 total, ~7–10 in this domain), expect 2–3 from this objective — we provide 43 practice questions to prepare you well beyond it. (estimate)

43questions here

9free pages

7concepts

Questions 11–15

11application · medium
A Java web service uses RSA-OAEP for encrypting sensitive payloads. When decryption fails, the service returns an HTTP 400 with a message that distinguishes 'Invalid ciphertext' from 'Invalid padding'. An attacker exploits this to recover the plaintext. What is the primary defensive coding fix?
Select an answer first
12application · medium
A security team is reviewing a Java codebase for cryptographic weaknesses. They want to identify hardcoded keys, weak algorithms, and improper random number generation. Which testing approach would be most effective for this task?
Select an answer first
13expert · hard
A Java application accepts a hex-encoded IV from the client and uses it to decrypt data with AES-CBC. An attacker modifies the IV to alter the first block of plaintext. The application does not validate the IV length or format. Which defensive coding change is most effective?
Select an answer first
14expert · hard
A security team is testing a Java application that uses AES-CBC with PKCS#5 padding for encryption. They notice that the application returns different HTTP status codes for 'padding error' versus 'MAC mismatch'. They want to confirm whether the application is vulnerable to a padding oracle attack. Which testing approach would most conclusively demonstrate the vulnerability?
Select an answer first
15foundation · easy
Which of the following is a secure way to generate a cryptographic key in Java?
Select an answer first

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