Glossary¶
The terms used across PQBlocks, each in a sentence or two.
ACVP¶
ACVP (Automated Cryptographic Validation Protocol) is NIST's protocol and test-vector format for checking that an algorithm implementation produces the right results.
CNSA 2.0¶
CNSA 2.0 is the NSA's Commercial National Security Algorithm Suite 2.0: ML-KEM-1024, ML-DSA-87, LMS and XMSS, AES-256 and SHA-384/512, with transition deadlines from 2025 to 2033 depending on the system type.
Composite signature¶
A composite signature pairs a post-quantum and a classical signature (for example ML-DSA-65 with Ed25519) under one key and one verification decision; both must verify.
Crypto agility¶
Crypto agility is the ability to change cryptographic algorithms through configuration or a small, contained code change, without redesigning a system. It makes this and future migrations cheaper.
Cryptographically relevant quantum computer (CRQC)¶
A cryptographically relevant quantum computer is a quantum computer large and reliable enough to run Shor's algorithm against real RSA and elliptic-curve keys. None is known to exist; migration deadlines are set so systems move before one does.
Cryptography Bill of Materials (CBOM)¶
A Cryptography Bill of Materials is a machine-readable inventory of the algorithms, keys, protocols and certificates a system uses, typically in CycloneDX format. It is the basis for migration planning and audit.
CycloneDX¶
CycloneDX is an OWASP standard for bills of materials. Version 1.6 includes cryptographic assets, which is how CBOMs are written.
FIPS 140-3 and CMVP¶
FIPS 140-3 is the US standard for cryptographic modules, and the Cryptographic Module Validation Program (CMVP) is how accredited laboratories validate modules against it. No PQBlocks package is CMVP validated.
FN-DSA¶
FN-DSA is the forthcoming NIST signature standard (FIPS 206) based on Falcon, with smaller signatures than ML-DSA and a more delicate implementation.
Grover's algorithm¶
Grover's algorithm is a quantum search algorithm with a quadratic speed-up. It roughly halves the effective strength of symmetric keys, which is why CNSA 2.0 requires AES-256 rather than AES-128.
Harvest now, decrypt later¶
Harvest now, decrypt later is the attack of recording encrypted data today in order to decrypt it once a cryptographically relevant quantum computer exists. It makes post-quantum key establishment urgent for data that must stay confidential for years.
HQC¶
HQC is a code-based key-encapsulation mechanism that NIST selected in 2025 for standardisation as a backup to ML-KEM, built on different mathematics.
Hybrid key exchange¶
Hybrid key exchange combines a post-quantum KEM and a classical key agreement, such as ML-KEM-768 with X25519, and derives one secret from both, so the result stays secure if either component is broken.
Ising model¶
An Ising model assigns spins of +1 or −1 to variables and minimises an energy with pairwise couplings and local fields. It is equivalent to a QUBO up to a change of variables.
Key-encapsulation mechanism (KEM)¶
A key-encapsulation mechanism is a public-key scheme in which a sender uses the recipient's public key to produce a ciphertext and a shared secret, which only the recipient's private key can recover. It replaces Diffie–Hellman-style key agreement in post-quantum protocols.
Known-answer test (KAT)¶
A known-answer test runs an implementation on fixed inputs and compares its outputs with published expected values, catching implementation errors that random testing can miss.
liboqs¶
liboqs is the Open Quantum Safe project's C library of post-quantum algorithms. Several PQBlocks packages use it for ML-KEM, ML-DSA and SLH-DSA rather than re-implementing them.
ML-DSA (FIPS 204)¶
ML-DSA is the NIST-standard lattice-based digital signature algorithm, formerly CRYSTALS-Dilithium. ML-DSA-65 has a 1,952-byte public key and a 3,309-byte signature; ML-DSA-87 is the CNSA 2.0 parameter set.
ML-KEM (FIPS 203)¶
ML-KEM is the NIST-standard lattice-based key-encapsulation mechanism, formerly CRYSTALS-Kyber. ML-KEM-768 has a 1,184-byte public key, a 1,088-byte ciphertext and a 32-byte shared secret; ML-KEM-1024 is the CNSA 2.0 parameter set.
NIST IR 8547¶
NIST IR 8547 is NIST's draft guidance on transitioning to post-quantum cryptography. It deprecates 112-bit quantum-vulnerable algorithms after 2030 and disallows quantum-vulnerable public-key algorithms after 2035.
Post-quantum cryptography (PQC)¶
Post-quantum cryptography is public-key cryptography designed to resist attacks by large quantum computers while running on ordinary computers. The first NIST standards are ML-KEM, ML-DSA and SLH-DSA.
Quantum-inspired optimisation¶
Quantum-inspired optimisation is classical algorithms modelled on quantum dynamics, such as annealing or bifurcation, run on ordinary hardware. It involves no quantum computer and has no security role.
QUBO¶
A QUBO (quadratic unconstrained binary optimisation) problem minimises a quadratic function of binary variables. Many scheduling, routing and selection problems can be written this way.
SARIF¶
SARIF (Static Analysis Results Interchange Format, OASIS 2.1.0) is a JSON format for static-analysis findings that code-scanning tools such as GitHub code scanning can display.
Shor's algorithm¶
Shor's algorithm is a quantum algorithm that factors integers and computes discrete logarithms in polynomial time, which breaks RSA, Diffie–Hellman, DSA and elliptic-curve cryptography.
Simulated bifurcation¶
Simulated bifurcation is a quantum-inspired classical heuristic (Goto et al., 2019 and 2021) that evolves continuous oscillators which bifurcate into ±1 states to find low-energy Ising solutions.
SLH-DSA (FIPS 205)¶
SLH-DSA is the NIST-standard stateless hash-based signature algorithm, formerly SPHINCS+. Its security rests only on hash functions; signatures are large (7,856 bytes for SLH-DSA-SHA2-128s).
Wycheproof¶
Wycheproof is a collection of test vectors for known attacks and edge cases in cryptographic libraries, such as malformed inputs and invalid curve points.
X25519MLKEM768¶
X25519MLKEM768 is the hybrid key-exchange group used in TLS 1.3 that combines X25519 with ML-KEM-768. It is the most widely deployed post-quantum mechanism on the web.