Postkvant

Postkvant, or postquantum cryptography (PQC), is the field of cryptography concerned with designing algorithms that remain secure against quantum computer attacks. The term is used in some contexts to refer to this area of study, which focuses on public-key encryption, key exchange, and digital signatures that resist quantum adversaries.

Quantum computers threaten many widely used public-key systems because Shor's algorithm can break RSA, Diffie-Hellman, and ECDSA, while Grover's algorithm can speed up brute-force attacks on symmetric keys. PQC researchers therefore develop alternative primitives based on mathematical problems believed to be hard for quantum computers.

Algorithm families in PQC include lattice-based cryptography (with Kyber for key encapsulation and Dilithium for signatures), code-based, hash-based, multivariate quadratic, and isogeny-based schemes. Kyber and Dilithium have gained prominence as leading candidates in standardization efforts; other schemes such as Falcon (lattice-based), Rainbow (multivariate), and SIDH/SIKE-based proposals have played roles in evaluations but are not yet standardized.

Standards and adoption: In 2022, the National Institute of Standards and Technology (NIST) selected Kyber and Dilithium as the first PQC standards for key encapsulation and digital signatures, respectively. Deployments often use hybrid schemes that combine classical and PQC algorithms to ease migration. Typical parameter sizes involve public keys and ciphertexts on the order of kilobytes, with signatures also several kilobytes, along with higher computational and memory requirements than some legacy schemes.

Deployment challenges and future directions: Ongoing work addresses security proofs, side-channel resistance, interoperability, hardware acceleration, and long-term security guarantees. As quantum hardware progresses, organizations plan gradual migration through hybrids and standardized PQC algorithms, while research continues to broaden the selection of validated postquantum primitives.