Why Decentralized Identifiers are Essential for FL Participants

Federated learning lacks participant identity. Current models treat data contributors as anonymous nodes, creating a sybil attack surface. A malicious actor can spawn thousands of fake clients to poison the global model or extract private gradients.

Decentralized Identifiers (DIDs) are the root-of-trust. Protocols like Iden3 and Spruce's Sign-In with Ethereum provide a cryptographically verifiable, self-sovereign identity. This anchors a participant's reputation and contribution history across training rounds.

DIDs enable slashing and rewards. A verifiable credential system, built on standards from the W3C or DIF, allows coordinators to penalize malicious nodes and reward high-quality data providers. This creates a cryptoeconomic security layer absent in traditional FL.

Evidence: The OpenMined community's research shows model accuracy degrades by over 30% under sybil attacks, a flaw mitigated by integrating DID-based attestations from projects like Ontology.

Sybil resistance is foundational. Without a cryptographically-secured unique identity, a social graph collapses into spam and manipulation, rendering reputation and curation meaningless. This is the primary failure mode of Web2 platforms.

Farcaster's FID is infrastructure. It provides a globally unique, user-owned identifier that persists across clients and applications. This enables portable social capital, unlike Twitter's platform-locked handles or Lens Protocol's NFT-based profiles.

Compare FID to ENS. An Ethereum Name Service domain is a premium, tradable asset. A Farcaster ID is a cheap, non-transferable primitive. One monetizes identity, the other operationalizes it for network integrity.

Evidence: Farcaster's 20M+ casts with minimal spam demonstrate the system's efficacy. The protocol's on-chain registry (Id Registry) and off-chain hub architecture separate identity from data, a design mirrored by systems like Ceramic Network.

DIDs decouple identity from platforms. A Farcaster user's social graph and reputation must persist across clients and applications, not be locked to a single interface. This requires a self-sovereign identity standard like W3C DIDs, which creates a cryptographic root for all user data.

Portable reputation demands cryptographic proof. On-chain activity from Lens Protocol interactions or Farcaster casts becomes a verifiable credential. DIDs allow users to prove their social capital without relying on a central API, enabling trust in decentralized social finance (DeSoFi) applications.

The alternative is fragmented pseudonymity. Without DIDs, users are reduced to disposable wallet addresses on each platform. This prevents the accumulation of sybil-resistant social graphs, which are essential for governance, curation, and anti-spam mechanisms in FL ecosystems.

Evidence: The Ethereum Attestation Service (EAS) and Veramo framework demonstrate the infrastructure shift. EAS facilitates on-chain, revocable attestations linked to a DID, creating a portable reputation layer that FL clients can query without central coordination.

Centralized identity providers fail because they reintroduce the single point of failure that decentralized social networks were built to eliminate. A provider like Privy or Magic can revoke keys, censor users, or go offline, breaking the user's social graph and asset access.

Protocols become permissioned platforms when identity is centralized. This contradicts the permissionless composability that makes Farcaster and Lens valuable. A centralized identity layer is a chokepoint that a DAO or corporation can control.

Decentralized Identifiers (DIDs) are the only solution that aligns with first principles. Standards like W3C DIDs and Verifiable Credentials enable self-sovereign identity, where cryptographic proofs, not a third-party API, grant access.

Evidence: The Farcaster FID is a number in a smart contract, but the associated signing key is often held by a centralized custodian. This creates a critical vulnerability where the social identity is decentralized in name only.