In cryptography, a key that is used within the context of a single session only is called what?

In cryptography, a key that is used within the context of a single session only is called what?

• A. ephemeral
• B. static
• C. master
• D. derived

Answer: (A)

Ephemeral keys are temporary, created for a single session and discarded afterward. This one-session use is what gives forward secrecy, since even if a server’s long-term keys are later compromised, past session data protected by ephemeral keys remains secure. In practice, protocols may use ephemeral key exchange such as Diffie-Hellman ephemeral (DHE) or Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) to achieve this behavior. Static keys are long-term and reused across sessions, so they don’t provide the single-session property. A master key is typically a long-term key from which other keys are derived for a session, not the session key itself. Derived keys are produced from some base material via a key derivation function, which can be reused across sessions depending on the setup. Ephemeral specifically denotes a key intended for one session only.

Ephemeral keys are temporary, created for a single session and discarded afterward. This one-session use is what gives forward secrecy, since even if a server’s long-term keys are later compromised, past session data protected by ephemeral keys remains secure. In practice, protocols may use ephemeral key exchange such as Diffie-Hellman ephemeral (DHE) or Elliptic Curve Diffie-Hellman Ephemeral (ECDHE) to achieve this behavior.

Static keys are long-term and reused across sessions, so they don’t provide the single-session property. A master key is typically a long-term key from which other keys are derived for a session, not the session key itself. Derived keys are produced from some base material via a key derivation function, which can be reused across sessions depending on the setup. Ephemeral specifically denotes a key intended for one session only.