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Seres István András

@Istvan_A_Seres

🚀New paper: Private Delegation of (Non-)Membership Proof Updates in Cryptographic Accumulators Ever tried to use accumulators in practice? Then you’ve hit the wall: every update breaks everyone’s proofs. We fix that. 🧵1/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 🔥The core problem: Cryptographic accumulators compress huge sets (e.g., set of unspent coins) into tiny digests. But… when the set changes: ➡️ ALL membership proofs become outdated ➡️ Clients must recompute them This kills usability for mobile/offline users. 2/n

Seres István András

@Istvan_A_Seres

This isn’t just annoying — it’s fundamental. Recent lower bounds show: 👉 You can’t avoid frequent proof updates without blowing up the state size. So the question becomes: Can we privately outsource (non-)membership proof updates? 3/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz Naively outsourcing fails!❌ If you send your (non-)membership proof to a server: 👉 it can brute-force which element you own. Privacy = gone. Even worse in systems like Zcash, anonymous credentials, or key transparency. 4/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 💡Our idea: Let clients delegate (non-)membership proof updates to an untrusted server… BUT: 🔒 without revealing which element they care about ⚡ with constant client work ✅ and publicly verifiable correctness 5/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz We introduce a new primitive: 👉 Private delegation of accumulator proof updates Formalized with: • correctness • delegation soundness • (strong + weak) privacy guarantees 6/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 🧠 Key trick: Before sending a (non-)membership proof to the server, the client: 👉 blinds it The server updates the blinded (non-)membership proof → learns nothing about the underlying element 7/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz Then: ✔ Server returns updated blinded proof ✔ Anyone can verify the update was correct ✔ Client unblinds → gets valid fresh (non-)membership proof All without revealing the element x 👀 8/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz ⚡Performance highlight: Client update cost: 👉 O(1) (constant time!) Previous work: 👉 O(k) or even O(sqrt(k)) This is a huge win for resource-constrained devices. 9/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 🏗 We build concrete schemes for: • RSA accumulators • Bilinear accumulators Both supporting efficient private delegation for (non-)membership proofs. 10/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz For RSA accumulators: ✨ Simple but powerful trick: Randomize proof → exponentiate → prove consistency with NIZKs Result: ✔ efficient ✔ practical ✔ ~7% overhead vs non-private baseline 11/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz We also support: ✔ membership proofs ✔ non-membership proofs ✔ batching of updates All privately delegated. 12/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 🧾 Public verifiability is key: The server can produce a proof that: 👉 “I updated this correctly” Anyone can check it. This enables: 💰 markets for proof-serving nodes. 13/n

Seres István András

@Istvan_A_Seres

🧠 Why this matters: Applications include: • Stateless blockchains • Anonymous credentials (revocation) • Registration-based encryption • Transparency logs 14/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz Example: stateless blockchains Without our approach: 👉 you must stay online to keep proofs fresh With us: 👉 go offline, come back, outsource updates privately It turns out that running a server for delegating proofs in a stateless blockchain is pretty cheap. 15/n

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Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz 🧪Bonus: We built an open-source implementation🔧 👉 First real system for private accumulator proof delegation 3...2...1...Delegate! <a target="_blank" href="https://github.com/GlaszBoti/private-accumulator-proof-delegation" color="blue">github.com/GlaszBoti/priv…</a> 16/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz Open problems, directions Private delegation for other authenticated data structures: vector commitments, authenticated dictionaries, etc. Private delegation for PQ-secure accumulators Multi-server private delegation schemes for better liveness 17/n

Seres István András

@Istvan_A_Seres

@0xSooki @BotiGlasz Let us know if you have any comments, feedback, critique, etc. Tolle, lege: <a target="_blank" href="https://eprint.iacr.org/2026/832.pdf" color="blue">eprint.iacr.org/2026/832.pdf</a> Q.E.D. Fin! 18/18