A few reflections on the lattice vs. hash-only debate that our recent Aerie post sparked: 1. Cryptographic ossification for blockchains was never safe. Until the day we know with certainty that P ≠ NP, that finding short vectors in lattices is intractable, that Keccak effectively behaves like a random oracle in deployed SNARKs, and that every single bug has been eliminated from our codebases, blockchains cannot ossify. That is simply not how safe systems are built. Issues will arise, and the system will have to respond. It’s a double standard to reject lattices because blockchains are hard to upgrade if lattices break, while counting on upgrades if AI breaks your hash function or finds a critical zkVM bug. The best counterargument is that hash-only designs are more agile: if your hash function breaks, just swap out the hash. But we must aspire to a higher level of agility than this. Indeed, as I cover next, if SNARK recursion itself turns out to degrade security, the proposed hash-only blockchain designs would need to be rethought from the ground up. 2. The real security debate is not lattices vs. hashes — it is lattices vs. building everything on SNARK recursion. That’s because “hash-only” is not really hash-only: it rests on hashes plus the soundness of deep SNARK recursion. Ethereum’s roadmap relies on exactly that: hash-based aggregation needs recursion to keep up with a slot’s worth of signatures, and EIP-8288 would send other signature schemes and users’ own proofs through the same recursive pipeline. In contrast, Aerie proves a slot’s worth of signatures on one laptop without any recursion. All deployed post-quantum SNARKs rely on the Random Oracle Methodology (via Fiat–Shamir) to establish their security. This is an idealization we know fails in the real world: we have explicit counterexamples where “SNARKs” coming out of this methodology are totally insecure when instantiated with any concrete hash function. We generally ignore these counterexamples in part because they only arise when proving contrived, self-referential statements about the very hash function used by the SNARK verifier. But proving statements about the verifier’s own hash function is the exact thing you do in SNARK recursion. That’s why the security of recursive SNARKs can’t be established even in the random oracle model. On top of that, the standard security proofs for recursion (in other models) suffer an “extractor runtime” blowup that is exponential in the recursion depth, suggesting that security may degrade as more recursion is applied. Yet Ethereum’s own EIP-8288 enables unlimited-depth recursion, even as it lists soundness of recursive SNARKs as a trust assumption. Proofs in more idealized models avoid the blowup, but they mainly tell us that an attack on SNARK recursion would have to exploit the concrete hash function, which is exactly what the Fiat–Shamir attacks above do. To be clear, we don’t know of any outright attacks on SNARK recursion, and I very much hope it is secure. But some of us who have studied the question have a lingering sense that an attack may be possible in some settings. And if AI is going to supercharge cryptanalysis, there is no reason to expect it to spare Fiat–Shamir for SNARKs, let alone SNARK recursion, both of which have had far less scrutiny than lattices. So, I do not concede that a “recursion everywhere” hash-only approach is clearly more conservative than one built on standard lattice assumptions. 3. “Just wrap everything in a hash-based SNARK” (like EIP-8288) faces challenges. Aggregating signatures and proofs off-chain into a single block-level proof is a powerful design independent of the hash-only vs. lattice debate, and I am not telling people to avoid it. But claiming, as Vitalik Buterin did this week, that users can run whatever cryptography they want locally and wrap it in a client-side leanVM proof glosses over major hurdles. For example, leanVM today is a minimal VM designed almost entirely to prove hash-based signatures and recursion, not general-purpose computation. And binary-field SNARKs like leanVM remain slow at proving the integer multiplications that lattice cryptography does en masse. I am optimistic that many of these zkVM challenges can be met (including via my own work, binary-field Twist and Shout, which are now implemented in Magnetar). But regardless, if lattices can make aggregation simpler and faster, then they should be leveraged. We need to be agile no matter what. 4. For chains whose reason for existence is privacy, I truly struggle to understand the pushback. Public-key encryption (and fast single-server PIR) cannot be built from hashes alone, at least not in any black-box way. If lattices break, it is going to be very, very hard for these chains to provide acceptable levels of privacy and functionality. For a project whose entire reason for existence is privacy, a loss of confidentiality is an existential failure. Next to that, a second signature upgrade (after the first one, from elliptic curves alone to, hopefully, a hybrid lattice scheme) is easy. Summary: We don’t know for sure what is secure and what isn’t. We are all weighing unquantifiable risks against each other, and we do not need to agree on a total order on them. But hash-only solutions face many open engineering challenges, and they are not more “conservative” in the way some have argued. Some of those challenges are entirely prosaic and have nothing to do with bugs or cryptography, like hardware support for custom schemes whose hash function is still undecided. I hope we can overcome those challenges within the appropriate timelines, but they must be acknowledged and portrayed realistically. Overall, cryptographic agility and defense in depth (e.g., hybrid signatures) are the answer, which is why we are building both lattice-Jolt and hash-Jolt. In practice, the positions are less polarized than social media discourse suggests: for example, StarkWare is working to make Falcon verification cheap (falcon.provably.fast/), which is great to see. Here is the (apparently) controversial take I am sticking to: Conditioned on agility, whenever lattices make systems simpler or more functional, we should embrace them rather than default to “hash-only” designs. Lattices are what the rest of the world will depend on, with decades of study and hardening behind them, and at the system level, less functional often means less secure. Where hash-only designs are just as simple and functional, by all means use them.

Goodbye, Poseidon! An epic 8-year, 8-figure rabbit hole in post-quantum cryptography reaches its dream conclusion. The Ethereum Foundation is abandoning Poseidon for L1, pivoting to SHA or BLAKE. This milestone unlocks ultimate security for lean Ethereum and foreshadows a golden era of hash-based cryptography. Since 2018, the Ethereum Foundation has invested in magic cryptographic bricks, so-called "SNARK-friendly hashes". In 2019, Poseidon was born. It held strong and became the dominant SNARK-friendly hash, securing billions via zkrollups and zkVMs. In a stunning reversal, breakthrough SNARK designs show that SNARK-friendly hashes aren't necessary after all. Off-the-shelf traditional hash functions like SHA2 and BLAKE2s can now match Poseidon in a SNARK. In hindsight the key was not SNARK-friendly hashes, but hash-friendly SNARKs. The secret is doing maths over the smallest prime number: 2. So-called "binary fields" natively speak the language of bits, aligning with the boolean operations inside traditional hashes. This is a stark departure from "prime fields", where awkward large-prime arithmetic makes bit manipulation painfully expensive. We're talking sci-fi cryptography. 1M traditional hash calls proven per second, on a laptop. Just 100x overhead vs native CPU boolean compute. Nobody predicted such performance, not even the handful of binary-field visionaries. Hat tip to the research geniuses: Jim and Ben with Binius in 2023; Ron, Benedikt and William with Flock in June. With SHA2, the lean aesthetic of minimal assumptions reaches its climax. The EF's principled stance on pure hash-based cryptography has aged like fine wine. We now enjoy foundations the world can trust for decades and centuries, foundations worthy of the dream of an internet of value. Speed of deployment is a secondary win. There's no longer a need to wait years for Poseidon cryptanalysis to bake. Emile and Thomas from the EF post-quantum team are moving at breakneck speed with binary fields. The strawmap now points to a production-grade leanVM in 2027, with CL, DL, EL deployments in 2028. As AI becomes exceptional at cryptanalysis, the contrarian bet to avoid riskier structures like lattices and isogenies is visibly paying off. The past weeks have been brutal. Lattice-based "HAWK" and isogeny-based "SQIsign", both signature schemes in NIST's Round 3, have suffered blows. Sources I trust say more blood is coming. On AI, the open autoresearch trend kicked off by ECDSA[.]fail is spreading fast, with amazing outcomes from zk[.]golf and SNARK[.]fast. Days ago SNARK[.]fast crossed 1.8M BLAKE3/sec proven on an M3 Max. Stay tuned for fresh autoresearch challenges dropping tomorrow. Also tomorrow: Ethproofs call #10, dedicated to binary fields. Possibly the most noteworthy Ethproofs call yet. Experts leading the charge will present the future of hash-based SNARKs at 2pm UTC. What an incredible time to be alive. To witness history, DM me for a calendar invite :) Today I can confidently claim that hash-based cryptography has won out for blockchain post-quantum signatures. SNARK succinctness compresses arbitrarily many signatures into one small proof per block. SNARK flexibility yields k-of-n threshold signatures, complex multisigs, and more. Ultimate security. Uncompromising performance. Full programmability. Believe in something. Believe in hashes.