tigro: Trust Infrastructure for Grassroots Organizing via Grounded Digital Annotations
Authors: Leah Namisa Rosenbloom (Northeastern University), Seny Kamara (Brown University and MongoDB Research), Zachary Espiritu (MongoDB Research), Tarik Moataz (MongoDB Research), Amine Bahi (École Normale Supérieure), John Wilkinson (Brown University)
Volume: 2026
Issue: 2
Pages: 354–383
DOI: https://doi.org/10.56553/popets-2026-0052
Abstract: Grassroots organizing requires establishing trust in digital artifacts (like event announcements or calls to action) while navigating significant security threats including surveillance, infiltration, and state violence. Traditional trust infrastructures like PKI and Web of Trust fail to address these specific needs, as they create public records of trust relationships that can expose activist networks and require institutional involvement that may be inaccessible or dangerous for marginalized communities.
To address this, we introduce tigro, a novel trust infrastructure and system designed specifically for grassroots organizing contexts. Unlike conventional trust infrastructures, tigro implements a two-tier trust model: ground trust, which cryptographically binds digital annotations to physically vetted individuals, and artifact trust, which enables private, need-to-know sharing of assessments about digital content via annotations. Our protocol begins with an in-person key exchange that establishes a shared cryptographic key, creating a secure bridge between activists' existing physical vetting practices and their digital trust needs.
To realize this approach, we define a new cryptographic primitive called an encrypted annotation system (EAS) and construct tigro using structured encryption and anonymous channels. We present two implementations with different security-performance tradeoffs: an efficient version for practical deployment that handles annotations in under a second, and a subliminal version that reveals virtually no metadata. Through this design, tigro enables activists to securely verify digital content without compromising relationship privacy or creating surveillance vulnerabilities, addressing a critical gap in existing trust infrastructure.
Keywords: grassroots organizing, activism, trust infrastructure, encrypted annotation system
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