GSEC Cryptography Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  PSK authentication cannot be used with IKEv2; it requires IKEv1.

  Why it's wrong here

  IKEv2 fully supports pre-shared key authentication. This option is factually incorrect; both IKEv1 and IKEv2 can use PSKs. The concern is not protocol support but the security weaknesses of PSKs. Therefore, this option is not a valid primary security concern.

• ✗

  PSK authentication does not encrypt the IKEv2 handshake, exposing the PSK in plaintext.

  Why it's wrong here

  The IKEv2 handshake is encrypted after the initial exchange, and the PSK itself is never sent in plaintext. Instead, it is used to generate authentication payloads. So the PSK is not exposed directly. The actual risk is offline dictionary attacks, not plaintext exposure. This option misrepresents how PSK authentication works.

• ✓

  PSK authentication is vulnerable to offline dictionary attacks if an attacker captures the handshake.

  Why this is correct

  In IKEv2 with PSK, the authentication exchange involves a hash of the PSK and other values. An attacker who captures the handshake can perform an offline dictionary attack to recover the PSK if it is weak. This is a serious concern because PSKs are often human-chosen and may be susceptible to guessing. Unlike certificate-based authentication, there is no public key infrastructure to provide strong authentication.

• ✗

  PSK authentication does not provide perfect forward secrecy (PFS).

  Why it's wrong here

  Perfect forward secrecy is a property of key exchange, not authentication. IKEv2 with PSK can still use Diffie-Hellman for key exchange to achieve PFS. The primary concern with PSK is not the lack of PFS but the fact that the same secret is shared among multiple parties, increasing the risk of compromise. So this option misidentifies the main issue.