Also known as: perfect forward secrecy · PFS
Forward secrecy is a property of encryption protocols ensuring that if a long-term private key is later compromised, past recorded sessions still cannot be decrypted, because each session used ephemeral keys that were discarded afterwards.
Without forward secrecy, an adversary can record encrypted traffic today and decrypt all of it retroactively if they obtain the server's private key at any point in the future — a 'harvest now, decrypt later' strategy that is entirely practical for well-resourced actors.
Modern protocols including TLS 1.3 and the Signal protocol provide forward secrecy by default. Signal's double ratchet extends the idea further with post-compromise security, where the session recovers confidentiality even after a key compromise.
End-to-End Encryption
End-to-end encryption (E2EE) is a system in which messages are encrypted on the sender's device and decrypted only on the recipient's, so that no intermediary — including the service provider — can read the content in transit or at rest on its servers.
TLS
TLS (Transport Layer Security) is the cryptographic protocol that encrypts data in transit between clients and servers, providing confidentiality, integrity, and server authentication — most visibly as the S in HTTPS.
Post-Quantum Cryptography
Post-quantum cryptography refers to cryptographic algorithms designed to remain secure against attacks by quantum computers, which would break the public-key algorithms such as RSA and elliptic-curve cryptography that currently secure most internet traffic.
Encryption at Rest
Encryption at rest is the encryption of stored data — on disks, in databases, or in backups — so that physical access to the storage medium does not yield readable data.