Summary:
Input Output (IO) recently co-organized the third edition of the Cryptographic Tools for Blockchains (CTB '26) workshop in Rome, alongside Eurocrypt 2026. The full-day technical event highlighted three critical pillars for the next generation of decentralized infrastructure:
- Post-quantum readiness: leveraging novel signature transformations and threshold constructions to preserve long-term network resilience.
- Verifiable state privacy: deploying advanced private information retrieval (PIR) regimes that guard data access layers without bottleneck baseline performance.
- Programmability without forks: extending the capabilities of existing networks like Bitcoin through witness encryption frameworks.
Together, these research streams build the secure, correct, and scalable foundations necessary for widespread institutional adoption.
About CTB'26
The third edition of the Cryptographic Tools for Blockchains (CTB'26) workshop was held in Rome in early May, alongside Eurocrypt 2026. The workshop gathered around 50 attendees – academics and practitioners from across the blockchain ecosystem – for a full day of technical presentations spanning zero-knowledge proofs, post-quantum cryptography, privacy, and blockchain programmability.
CTB '26 has established itself as a focused venue for bridging the gap between cutting-edge cryptographic research and its practical applications in blockchain systems. The third edition continued this tradition, bringing together researchers from leading institutions – including Stanford, EPFL, KU Leuven, the Ethereum Foundation, and others – alongside engineers building production systems. The program featured two keynotes and eight contributed talks organized across three sessions.
Technical tracks and highlights
Here is a closer look at the specialized technical tracks and standout highlights from the event:
Invited talks
Benedikt Wagner (Ethereum Foundation) opened the workshop with an overview of the state of multisignatures and aggregate signatures in Ethereum. Benedikt described the ongoing EF effort to combine post-quantum secure hash-based signatures (XMSS) with succinct non-interactive arguments of knowledge (SNARKs) as a path toward scalable signature aggregation – a construction called Hint-Free multi-signatures.
The afternoon invited talk, by Ali Atiia (Ethereum Foundation), addressed read privacy in blockchains. Querying blockchain state leaks information about which data is being accessed – a privacy problem often overlooked in protocol design. Atiia presented a system for private information retrieval (PIR) over Ethereum state, combining Unified Binary Trees (UBT) for compact state representation, SNARKification for verifiable query processing, and sharding plus preprocessing techniques to bring PIR into a practically feasible regime.
Morning track
- SNARKs for First-Order Logic (Gabbay and Mendelsohn, Imperial College London) showed how to arithmetize first-order logic formulas into constraint systems that SNARKs can process, using multilinear extensions.
- New Straight-Line Extractable NIZKPs for Cryptographic Group Actions (Pintore et al., University of Trento) revisited the Fiat-Shamir transform and its alternatives for converting interactive proofs to non-interactive ones. They introduced a new transform based on group actions – the GAO transform – that achieves straight-line extraction without rewinding. The result has near-optimal parameters for post-quantum signature schemes such as LESS, an isogeny-based scheme.
- DekartProof: Efficient Vector Range Proofs and Their Applications to Blockchains (Boneh et al., Stanford / Aptos) introduced a new construction for zero-knowledge range proofs over vectors, leveraging multilinear encodings and a novel ZK variant of the sumcheck protocol. Proving and verification are significantly faster than prior art, though at the cost of larger proof sizes.
- Trust, But Verify When Using the Powers of Tau (Baghery, KU Leuven) diagnosed a critical gap in how Powers of Tau ceremonies are run in practice. Since verifying the final structured reference string (SRS) naively takes thousands of seconds, ceremony participants routinely skip this step, undermining security guarantees. The paper presents a concrete algorithm and advocates for its adoption as standard practice.
- Monotone Erasure Codes (Cimatti, Bammert et al., University of Bern / Common Prefix / SDF) introduced a framework for constructing optimal erasure codes for arbitrary monotone access structures, formalizing the problem via linear programming. The construction is relevant to BFT consensus, secret sharing, and blockchain voting, among others.
Afternoon Track 1
- Sponsored Fair Exchange (Vaudenay, EPFL / CIMA.SCIENCE) presented Sponsored Optimistic Xchange (SOX), a protocol for fair digital goods exchange that achieves privacy and economic fairness. A key innovation is the sponsor role: third parties who subsidize blockchain fees on behalf of participants, enabling fee-free participation for vendors and buyers who only pay on successful transactions. Dispute resolution has logarithmic complexity in the number of knowledge coins exchanged.
- Balthazar: A Password-Based Web3 Wallet using OPAQUE and TEE with Brute-Force Resistance (Krajci, Oleksak, Homoliak, Brno UT / Slovak UT) tackled the UX gap between Web2 password authentication and Web3 key management. Balthazar implements the OPAQUE password-authenticated key exchange protocol inside a TEE-backed confidential EVM, with encrypted on-chain storage and blockchain-enforced rate limiting to prevent brute-force attacks.
Afternoon Track 2
- Bitcoin PIPES v2 (Abdalla, Carmer, El Gebali, Kilinc Alper et al., allocinit.xyz) extended the PIPES framework with Witness Encryption and Witness Signatures. The result increases Bitcoin's programmability – enabling rollups, bridges, vaults, and other constructions – without any protocol fork.
- Thresholding Post-Quantum Signatures (De Sclavis, Nardelli, Pedicini, Bank of Italy / Roma Tre) surveyed the state of threshold signatures in the post-quantum setting, covering lattice-based approaches (noise flooding, Lagrange coefficient issues), group-action and isogeny-based schemes, and hash-based constructions. The talk highlighted the significant open challenges remaining in each family before practical threshold post-quantum signatures become viable.
- Data Availability Sampling with Repair (Boneh, Neu, Nikolaenko, Partap, Stanford / a16zcrypto) augmented data availability (DA) sampling with repair capabilities: the ability to reconstruct data lost due to malicious or faulty nodes. The construction relies on locally correctable codes (specifically multiplicity codes) and a new multivariate polynomial commitment scheme, providing provable recovery guarantees for DA layers.
Ongoing research work
CTB'26 reflected both the maturity and the open frontiers of applied cryptography for blockchains. From practical ceremony hygiene to post-quantum threshold signatures, and from private state access to Bitcoin programmability, the workshop demonstrated the breadth of unsolved problems – and the depth of the ongoing work to address them. The slides used by the presenters are available on the CTB website.
