Modern Cryptographic Attacks ECES Practice Questions (Page 8)

Questions 36–39

1. 36expert · hard

   A security team is investigating a breach where an attacker was able to decrypt traffic between a client and server. The server supports both RSA key exchange and ephemeral Diffie-Hellman (DHE). The attacker is suspected of having recorded all encrypted traffic and later obtained the server's private key. Which key exchange method is most likely to have been used, and why?

   • ADHE key exchange, because it uses the server's private key to sign the ephemeral key, which can be recovered
   • BBoth RSA and DHE are equally vulnerable to this attack
   • CDHE key exchange, because it uses ephemeral keys that are not protected by the server's private key
   • DRSA key exchange, because it does not provide forward secrecy, allowing the attacker to decrypt recorded traffic after obtaining the private key
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2. 37expert · hard

   A security researcher is analyzing a smart card that uses RSA decryption. The researcher notices that the time taken to decrypt a message varies depending on the private key bits. The researcher also has physical access to the card and can measure its power consumption. Which side-channel attack is the researcher most likely to succeed with, and what is the best mitigation?

   • ACache-timing attack, because it is the most common side-channel on smart cards
   • BPower analysis attack, because the researcher has physical access and can measure power consumption directly
   • CElectromagnetic attack, because it is the most powerful side-channel and does not require physical contact
   • DTiming attack, because it is easier to perform remotely and requires no physical access
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4. 38application · medium

   A developer is implementing password storage for a new application. The developer uses SHA-256 without a salt to hash passwords. A security reviewer flags this as a serious flaw. Which attack is the developer's approach most vulnerable to, and what is the recommended fix?

   • AKey-reuse attack; use a unique key for each password
   • BPadding oracle attack; use a proper padding scheme
   • CTiming side-channel; use constant-time comparison
   • DRainbow table attack; use a salted, slow key-derivation function like bcrypt or Argon2
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5. 39foundation · easy

   Which of the following is a common implementation flaw that weakens a cryptographic system?

   • AUsing a well-vetted cryptographic library with regular security updates.
   • BStoring private keys in a hardware security module (HSM) with strict access controls.
   • CGenerating encryption keys using a deterministic algorithm seeded with the current timestamp.
   • DUsing a cryptographic algorithm that is considered secure by current standards, such as AES-256.
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