Hybrid cryptography
Combining a classical algorithm with a post-quantum one so the result stays secure as long as either component holds. It hedges against both a future quantum attack and an undiscovered flaw in the newer post-quantum scheme.
In practice
X25519MLKEM768 in TLS 1.3 combines classical X25519 with ML-KEM-768, and is widely deployed.
Related terms
The NIST-standardised post-quantum key encapsulation mechanism, used to establish a shared secret over an untrusted network. It is the replacement for RSA key transport and elliptic-curve Diffie-Hellman.
The ability to change cryptographic algorithms, parameters or libraries without redesigning the systems that depend on them. Agility is what turns the next migration from a rewrite into a configuration change.
The protocol securing most internet traffic. TLS is the furthest-advanced post-quantum migration in practice: hybrid key exchange combining X25519 with ML-KEM-768 is already enabled by default across major browsers and CDNs.