Most cryptographic systems only guarantee that a mathematical lock is hard to pick on average; Miklós Ajtai proved that breaking a random lattice lock requires an algorithm capable of solving the hardest geometric problem in the entire universe. Published in 1996, Ajtai’s worst-case to average-case reduction is the foundational mathematical theorem behind all post-quantum cryptography protecting global cybersecurity from quantum computers.

In classical cryptography, algorithms like RSA rely on factoring prime numbers, but mathematicians could never prove that every single RSA key was hard to crack—some randomly generated keys might secretly contain easy shortcuts that hackers could exploit.
Hungarian mathematician Miklós Ajtai constructed a mathematical fortress based on high-dimensional lattices. He proved a theorem: if a hacker invents an algorithm that cracks even a random, everyday lattice lock, that exact same algorithm can be used to solve the single most difficult geometric puzzle in the universe.
Ajtai’s reduction became the foundation for post-quantum security. By guaranteeing that lattice encryption contains no easy backdoor shortcuts, by resisting Shor’s quantum factoring algorithms, and by anchoring the new NIST post-quantum encryption standards (ML-KEM and Dilithium), Ajtai’s proof defends the future internet.
Generating hard instances of lattice problems (extended abstract)
. We give a random class of lattices in Z n so that, if there is a probabilistic polynomial time algorithm which finds a short vector in a random lattice with a probability of at least 1 2 then there is also a probabilistic polynomial time algorithm which solves the following three lattice problems in every lattice in Z n with a probability exponentially close to one. (1) Find the length of a shortest nonzero vector in an n-dimensional lattice, approximately, up to a polynomial factor. (2) Find the shortest nonzero vector in an n-dimensional lattice L where the shortest vector v is unique in the sense that any other vector whose length is at most n c kvk is parallel to v, where c is a sufficiently large absolute constant. (3) Find a basis b 1 ; :::; b n in the n-dimensional lattice L whose length, defined as max n i=1 kb i k, is the smallest possible up to a polynomial factor. A large number of the existing techniques of cryptography include the generation of a specific ins...
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