The NIST standardization process for post-quantum security started in 2016. At the time of writing (April 2026), two distinct approaches to post-quantum signature schemes are promising: hash-based or lattice-based, each one with different characteristics and tradeoffs. Any post-quantum algorithm poses some challenges to blockchain-constrained resources. Algorand must stay true to the original design principles: it must be secure, scalable, and decentralized. The size of post-quantum keys and signatures (bigger than the classical ones) could make running a node less accessible if the block size is increased (compromising decentralization), or could reduce performance (TPS) if the block size is preserved.
Algorand chose Falcon (lattice-based category) as it helps ensure post-quantum security while being aligned with Algorand's first principles.
Compact efficiency: Falcon remains post-quantum secure while possessing relatively small key and signature sizes—meaning there is less data to store and manage if compared to the hash-based category, making it compatible with resource-constrained devices, like smartphones and security chips in IoT devices, consuming less block space and bandwidth (crucial for Algorand decentralization and scalability).
Classical compatibility: While Falcon is designed to be secure against quantum computers, it still needs to remain performant on the classical computers that we use today. This means signing a message with your private key and verifying a signature with a public key should be fast enough for practical use, even on devices with less processing power, like mobile phones. Falcon signatures are extremely efficient and fast to verify, both at the protocol layer and application layer (Smart Contracts).
Endurance: Falcon can potentially be tweaked or integrated with other algorithms as the cryptography field evolves, ensuring its continued relevance even as new threats or solutions emerge.
A former Algorand Technologies cryptography engineer, Dr. Zhenfei Zhang, along with fellow collaborators, submitted two proposals to the National Institute of Standards and Technology (NIST) competition to establish new standards for post-quantum cryptography in 2016. These were NTRU, a public key encryption scheme, and Falcon, a digital signature scheme. Out of over 80 submissions from the world's top universities, researchers, and cryptographers, Falcon was ultimately selected as one of the NIST-endorsed digital signature algorithms in 2022.
Falcon is based on Trapdoors for Hard Lattices and New Cryptographic Constructions, the pioneering group public verification (GPV) work of Craig Gentry (former Algorand Foundation research fellow), Chris Peikert (Chief Scientific Officer at Algorand Foundation), and Vinod Vaikuntanathan (MIT professor).
In a GPV scheme and, in this case, lattice-based signatures, every message has many possible valid signatures, and a signing algorithm must ultimately choose only one of them. This proof can then be verified using a public key, without revealing any information about the individual secret keys used to create the original signatures. Traditional methods for choosing a single valid signature from many made it possible to recover the signing key from just a small number of signed messages, even using a classical computer.
The crucial innovation of the GPV work, which Falcon signatures use, is a rigorous method of selecting a valid signature in a way that reveals no information about the secret signing key. Using this method, it’s possible to safely sign a huge number of messages. Moreover, GPV showed that it is not possible to break the signature scheme without solving the lattice problem, which should be hard to solve for all computers, both classical and quantum.
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