Crypto Gloss

Polygon ID

Definition:

Polygon ID is a decentralized, ZK-native identity framework built on the Iden3 cryptographic protocol that enables users to hold verifiable credentials privately and prove statements about themselves (age, nationality, membership, KYC status) to on-chain smart contracts or off-chain applications via ZK proofs — without revealing the underlying credential data. Unlike simple token-gating, Polygon ID’s ZK proofs allow fine-grained, programmable credential logic (e.g., “prove you are over 18 AND reside in an eligible country”) while preserving full data privacy.

Core Protocol: Iden3

Polygon ID is built on Iden3, an open-source cryptographic identity protocol originally developed by the team behind Hermez (now Polygon Hermez). Iden3 provides:

  • Identity Tree — A Merkle-tree-based structure representing an identity’s claims
  • Baby JubJub curve — An elliptic curve optimized for ZK-SNARK (Groth16) circuit arithmetic
  • Claim schema language — A standardized JSON-LD schema for identity claims
  • Sparse Merkle Trees — Efficient inclusion/exclusion proofs for identity claims

Key Components

Issuer Node:

An organization (bank, DAO, exchange) that issues verifiable credentials to users. The issuer runs an Issuer Node (a server) that signs and stores credentials in its own identity tree on-chain.

Identity Wallet (Holder):

A user’s mobile or browser-based wallet that stores credentials issued to them. The wallet computes ZK proofs locally when presenting credentials so private data never leaves the device.

Verifier:

An application or smart contract that requests proof of a claim. The verifier specifies a Query — conditions that the credential must satisfy — and the user’s wallet generates a ZK proof that their credential satisfies the query.

On-chain Verification:

Polygon ID supports both off-chain (API-style) and on-chain verification. A smart contract can accept a ZK proof and gate access, execute a transaction, or award tokens based on verified identity claims — with no personal data on-chain.

Query Language

Verifiers specify queries using a lightweight DSL:

“`json

{

“circuitId”: “credentialAtomicQuerySigV2”,

“id”: 1,

“query”: {

“allowedIssuers”: [“*”],

“credentialSubject”: {

“birthday”: {

“$lt”: 20060101

}

},

“type”: “KYCAgeCredential”

}

}

“`

This asks: “Is the user’s birthday less than Jan 1, 2006 (proving they are 18+)?” The ZK proof confirms yes/no without revealing the actual birthday.

Privacy Design

Step Data Exposed
Credential issuance Issuer knows recipient DID and claim
Credential storage User’s wallet only
Proof generation Computed locally on user device
Proof submission Only ZK proof — no raw credential data
On-chain verification Proof + circuit output only

No personal data touches the blockchain. On-chain state only records identity commitments and proof verifications.

Identity Types

  • Regular Identity — User DID with Baby JubJub key pair
  • Ethereum DID — User’s Ethereum wallet address as the subject of credentials
  • Profile Identity — User creates separate profiles per application (like browser profiles) to prevent cross-app correlation

Use Cases

  • KYC gating without data sharing — A DeFi protocol requires verified users; Polygon ID verifies without storing actual KYC data
  • Voting eligibility — DAO proves a voter is unique and eligible via credential, not token balance
  • Age verification — Gaming or adult platforms verify age without collecting birthdates
  • Credential-based DeFi — Undercollateralized lending based on credit score VCs from traditional issuers
  • Healthcare — Patient shares relevant medical credentials with providers without full record disclosure

Ecosystem and Status (2024)

Polygon ID is production-ready and integrated into:

  • Polygon (PoS and zkEVM) as a native identity layer
  • Several DeFi protocols for KYC compliance
  • Gaming projects for eligibility gating

The framework is open-source; anyone can run an Issuer Node and design custom credential schemas.

Related Terms

Sources

Last updated: 2026-04