Building a Browser-Native Verification Stack for Tinfoil

Learn how we built a browser-based confidentiality and integrity verifier with implementations of browser-native Sigstore and TUF libraries.

badge.blue — CID-First Attestation Specification

Specification for CID-first attestations on AT Protocol records. Inline and remote cryptographic signatures with replay-attack prevention.

LEAF: Compact and Efficient Blind Signature from Code-based Assumptions

Recently, recent advancement in Asiacrypt'25, gives new blind signature frameworks, collectively named Tanuki(s), built upon cryptographic group actions. Their work introduces novel techniques and culminates in a concurrently secure blind signature framework. Straightforward instantiations based on CSIDH (CSI-FiSh) and LESS yield signature sizes of 4.5 KB and 64 KB respectively, providing the first efficient blind signatures in the isogeny-based and code-based literature allowing concurrent executions. In this work, we improve the code-based instantiations by using the canonical form of linear equivalent codes by a careful treatment. However, the canonical form does not naturally support a group action structure, which is central to the security proofs of Tanuki(s). Consequently and unfortunately, the original security guarantees do not directly apply. To address this, we develop two distinct non-black-box reductions for both blindness and the one-more unforgeability. In the end, the improvements do not compromise the security. This results in a concurrently secure code-based blind signature scheme with a compact signature size of 4.4 KB, which is approximately 1% smaller than the isogeny-based one. We also provide a C implementation where the signing time in 99ms and 268 Mcycles on an Intel i7 2.3~GHz CPU. We also look forward to our approaches benefiting advanced constructions built on top of LESS in the future.

Tutorial: Introduction to Formal Verification with Lean (Part 1) - HashCloak

A tutorial Formal Verification using Lean for cryptographic engineers. Implement and prove correctness of the One-Time pad following a cryptography book.

Breadcrumbs: physical attestations for ecosystem contributions

Hey atmospheric friends, over the weekend I started experimenting with physical attestations, as part of my exploration of an ATScience community labeller. breadcrumbs: physical objects — NFC tags, printed QR codes — that let someone attest to their own participation in something, or let an authority attest that someone did something specific. Two record types separate self-attested contributions (crumbs) from community-authored ones (badges). Lexicons: - `id.breadcrumbs.trail` — self-minted...

Backend infrastructure - Tinfoil Documentation

This page provides a description of the different components that make up our backend infrastructure. It also describes how Tinfoil guarantees code auditability and data confidentiality using these components.

Building Unforgeable Professional Endorsements with ATProtocol - Nick's Blog

Traditional professional endorsements on platforms like LinkedIn lack cryptographic proof—anyone could forge them, and the platform controls the truth. This article introduces a two-record architecture using ATProtocol's Content Identifiers (CIDs) and Decentralized Identifiers (DIDs) to create mathematically unforgeable mutual attestations. By separating proof creation from endorsement acceptance and leveraging the firehose for distributed validation, we build a system where both parties cryptographically consent and no central authority can manipulate the record.

War on CARs - Data service diaries

A widespread authenticity problem in the Authenticated Transfer Protocol, from real-world use of Content-Addressible aRchives

War on CARs - Data service diaries

A widespread authenticity problem in the Authenticated Transfer Protocol, from real-world use of Content-Addressible aRchives

tassis/atfield-core

Framework-agnostic AT Protocol utilities for identity resolution and public record reads.

SyRA: Sybil-Resilient Anonymous Signatures with Applications to Decentralized Identity

We study Sybil-Resilient Anonymous (SyRA) signatures, a cryptographic primitive that enables credentialed users to generate, on demand, unlinkable pseudonyms tied to any given context, and issue signatures on behalf of these pseudonyms. Concretely, SyRA allows a distributed issuer to turn any legacy identity or personhood identifier, possibly of low entropy, into a unique associated cryptographic key of high pseudoentropy, for use in generating signatures for any given context. Sybil-resilient anonymous signatures achieve three main objectives: 1) Sybil resilience: every user is entitled to at most one digital identity, 2) anonymity: no information about the user’s real identity is leaked, and 3) non-interactive context switching: users can create on their own at most one credential for any given context in a manner that is unlinkable across contexts. We conceptualize the SyRA primitive as an ideal functionality in the Universal Composition (UC) setting and put forth SASSI, an efficient, pairing-based construction that realizes it by utilizing two levels of verifiable random functions (VRFs), a design which may be of independent interest. The first level consists of threshold VRF issuance of a user’s unique secret key tied to their real-world identifier. The second level allows a user to create signatures for each context, under a unique pseudonym per context. Compared to prior cryptographic tools capable of realizing SyRA, SASSI has the unique feature that issuers are stateless and hence do not need to retain any information about past user interactions, a relevant property for a decentralized implementation. We overview various applications of SASSI in multiparty systems, such as cryptocurrency account management and airdrops, e-voting (e.g., for decentralized governance), and privacy-preserving regulatory compliance (e.g., AML/CFT checks). In the context of creating addresses for digital assets, SyRA signatures enable users to embed their legacy identity into their address in a manner that protects their privacy for each application with which they interact. We demonstrate the practicality of SASSI by providing an implementation and performance evaluation of our construction.

Compare CIRIS: Verifiable Ethical AI vs the Alternatives, With Receipts

How CIRIS's signed, on-device, checkable ethical AI stacks up against the alternatives — the safety case, with receipts.

Introducing Automatic Key Verification

Signal now offers a feature called “automatic key verification” which complements the existing safety number system. Signal is always end-to-end encrypted, and automatic key verification provides an additional, streamlined way to confirm that there’s no unexpected party between you and the other ...

ATProtocol Attestations: Cryptographic Signatures for the Decentralized Web - Nick's Blog

This post introduces the formal ATProtocol attestation specification, a framework for adding cryptographic signatures to ATProto records through two complementary patterns: inline attestations that embed signatures directly in records, and remote attestations that store proof in separate repository records. The specification prevents replay attacks through repository binding, uses CID-based content addressing for integrity, and provides the cryptographic foundation for verified credentials, trusted content, and authenticated interactions in the decentralized ATProtocol ecosystem.

Unforgeable Endorsements Technical Deep-Dive - Nick's Blog

Deep technical implementation of the unforgeable endorsement system. Covers step-by-step CID computation, complete code for the endorsement workflow, validation algorithms, firehose event processing, and detailed security analysis of attack vectors. Includes working code examples, lexicon definitions, and the cryptographic mechanisms that make forgery mathematically impossible.