SSCP 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.

• ✗

  Use static keying with manually configured security associations and AES-256.

  Why it's wrong here

  Static keys are long-term secrets; if one is compromised, all traffic encrypted under it is exposed, and there is no forward secrecy. Manual security associations also lack scalability and rekeying. AES-256 provides strong encryption but does not address key compromise retroactively. This approach completely fails the PFS requirement.

• ✓

  Use IKEv2 with a Diffie-Hellman group for the IKE SA and a separate Diffie-Hellman group for the CHILD_SA.

  Why this is correct

  Perfect forward secrecy is achieved when each session key is derived from a fresh Diffie-Hellman exchange rather than from a long-term key. In IKEv2, using a DH group for the IKE SA and a distinct DH group for the CHILD_SA ensures that compromise of the IKE SA key does not compromise the IPsec session keys. This provides the required PFS.

• ✗

  Use IKEv2 with RSA signatures for authentication and no additional Diffie-Hellman exchange after the initial IKE SA.

  Why it's wrong here

  RSA signatures authenticate the peers but do not by themselves provide PFS. If the CHILD_SA keys are derived solely from the initial IKE SA without a fresh DH exchange, then compromise of the IKE SA key could expose child keys. PFS requires an ephemeral DH exchange for each child SA, which this configuration lacks.

• ✗

  Use IKEv1 in main mode with pre-shared keys and no DH group for the quick mode.

  Why it's wrong here

  IKEv1 main mode with pre-shared keys can use DH for the phase 1 exchange, but omitting a DH group in quick mode means the IPsec session keys are derived from the phase 1 keying material. If the long-term pre-shared key or the phase 1 key is later compromised, past session keys may be derivable. This does not provide PFS for the IPsec SAs.