CompTIA Exam Prep - ITF+, A+, Network+, Security+, CySA+

Forward secrecy means that compromising a long-term private key does not reveal past sessions. Each session's key is generated fresh and destroyed afterwards, so an attacker who obtains the server's key next year cannot decrypt the traffic they recorded this year. The problem it solves Older TLS used the server's RSA key directly for key transport: the client generated a session key, encrypted it with the server's public key, and sent it. Anyone holding the server's private key could decrypt that message and recover the session key. So an attacker recording traffic today and obtaining the private key later — through a breach, a subpoena, a departing administrator, or a flaw in the key's generation — could decrypt everything retroactively. One key compromise exposed years of sessions. Ephemeral key exchange removes that. The session key is derived through a fresh Diffie-Hellman exchange, the private values are discarded when the session ends, and the server...

PGP is a hybrid cryptosystem for encrypting and signing files and messages, and GPG is its widely used free implementation. Technically it has aged well; as an email encryption scheme it never achieved broad adoption, and the reasons are instructive about usability as a security property. How the hybrid scheme works PGP does not encrypt a message with the recipient's public key directly — asymmetric operations are far too slow for bulk data. Instead it generates a random symmetric session key, encrypts the message with that, then encrypts the session key with each recipient's public key and attaches the results. Each recipient uses their private key to recover the session key, and the session key to read the message. This is the same pattern TLS uses and the standard arrangement described under asymmetric encryption : asymmetric for key establishment, symmetric for the data. It is also why adding a recipient is cheap — one more encrypted copy of a small key rather than ...