Q6 /20 Which is the cryptographic algorithm of forward secrecy (FS)?

Forward Secrecy (FS) is a cryptographic property that ensures session keys derived from short-term parameters remain secure even if long-term keys are compromised. Option B correctly defines this core principle: past encrypted data remains protected because it was encrypted with ephemeral session keys, not the compromised long-term key. Options A, C, and D describe key management risks, computational strength, and technological advancement respectively—none capture the essence of forward secrecy's isolation mechanism.

Step-by-step Derivation:
Forward Secrecy works by generating unique session keys for each communication session using ephemeral (temporary) key material. Even if an attacker obtains the long-term private key later, they cannot retroactively decrypt past sessions because those sessions used different, one-time session keys that are no longer available. This is the fundamental guarantee of FS: temporal isolation of session keys from long-term keys. Option B is the only choice that articulates this protective mechanism.