Foundations

The concepts behind the field: the quantum threat, the algorithm families, and why public-key cryptography is being replaced.

12 entries

Code-based cryptographyCode-based cryptography builds encryption on the hardness of decoding random linear codes, from McEliece in 1978 to the NIST-selected HQC KEM.
Grover's algorithmGrover's algorithm gives quantum computers a quadratic speedup for unstructured search, weakening symmetric ciphers and hash functions but not breaking them.
Harvest now, decrypt laterHarvest now, decrypt later is an attack in which encrypted data is recorded today so it can be decrypted once quantum computers can break the encryption.
Hash-based signaturesHash-based signatures derive their security only from hash functions, spanning stateful XMSS and LMS and the stateless NIST standard SLH-DSA.
Isogeny-based cryptographyIsogeny-based cryptography builds on maps between supersingular elliptic curves; SIDH and SIKE were broken in 2022, leaving CSIDH and SQIsign.
Lattice-based cryptographyLattice-based cryptography builds encryption and signatures on hard lattice problems such as LWE and underpins the NIST standards ML-KEM and ML-DSA.
Multivariate cryptographyMultivariate cryptography builds signatures on the hardness of solving multivariate quadratic equations, from the broken Rainbow to the surviving UOV and MAYO.
Post-quantum cryptographyPost-quantum cryptography is the field of cryptographic algorithms designed to resist attacks by both classical computers and future quantum computers.
Q-DayQ-Day is the hypothetical future date when a cryptographically relevant quantum computer can break RSA and elliptic curve cryptography in practice.
Quantum computerA quantum computer processes information with qubits and quantum effects; current machines remain far from breaking deployed public key cryptography.
Quantum key distribution (QKD)Quantum key distribution (QKD) uses quantum physics to share encryption keys; the NSA and UK NCSC recommend post-quantum cryptography instead.
Shor's algorithmShor's algorithm factors integers and computes discrete logarithms in polynomial time on a quantum computer, breaking RSA, Diffie-Hellman, and ECDSA.