> For the complete documentation index, see [llms.txt](https://docs.zkid.digital/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zkid.digital/additional-information/glossary.md). # Glossary This glossary provides detailed definitions for concepts frequently referenced across ZKID’s documentation, architecture, and ecosystem design. *** #### **Anchoring** The process of hashing identity registry state and anchoring the hash to Bitcoin (SHA-256) for global immutability. Anchoring acts as ZKID’s censorship-resistant truth layer, ensuring state cannot be rewritten or manipulated. *** #### **Arweave** A decentralized long-term data storage network. ZKID uses Arweave to store compressed identity metadata, credential references, and historical snapshots for verifiable permanence. *** #### **Batching** A mechanism where multiple identity operations (updates, issuances, revocations) are grouped into minimal Solana transactions or compressed updates to increase throughput and significantly reduce gas costs. *** #### **CID (Content Identifier)** A cryptographic pointer used to reference off-chain data stored in decentralized storage systems (IPFS, Arweave). ZKID uses CIDs for credential payloads, metadata, VC attestations, encrypted proofs, and historical logs. *** #### **Compressed Identity State** Identity attributes, credentials, and metadata stored in Solana’s compressed accounts. Allows the registry to scale to millions of identity states while staying cost-efficient. *** #### **Credential Issuance** The process by which a trusted issuer signs a cryptographically verifiable credential for a user’s DID. In ZKID, issuance is modular, privacy-preserving, and instantly verifiable across apps. *** #### **Cross-Layer Synchronization** ZKID’s system for synchronizing identity updates between Solana’s real-time state and Bitcoin anchoring checkpoints. Ensures consistency without cross-chain trust assumptions. *** #### **Decentralized Identifier (DID)** A cryptographically verifiable identifier controlled entirely by the user. ZKID supports DID-linked credentials, selective disclosure, and cross-app verification flows. *** #### **Decentralized Storage** Storage systems outside centralized servers. ZKID uses a hybrid approach: * **Solana** for compressed identity state * **Arweave/IPFS** for metadata and proof payloads * **Bitcoin anchoring** for global state integrity *** #### **Identity Graph** A Merkle-structured representation of a user’s digital identity, composed of attributes, credentials, attestations, reputation signals, and verifiable proofs. *** #### **Identity Snapshot** A hashed representation of identity registry state captured at a given time and anchored to Bitcoin. Enables historical audits and verifiable lineage. *** #### **Merkle Compression** Solana’s compressed data structure enabling low-cost identity storage. ZKID uses Merkle trees to store identity state with minimal on-chain footprint and fast verification. *** #### **Nullifier** A cryptographic marker used to prevent double-signalling, replay attacks, or proof re-use in zk-based identity flows. Critical for ensuring uniqueness and non-repeatability. *** #### **Selective Disclosure** A mechanism that allows users to disclose **only** what is necessary.\ Examples: * "I am over 18" without revealing date of birth * "I own this NFT" without exposing wallet history * "I am human" without biometric leakage *** #### **Self-Sovereign Identity** A model where the user fully controls their identity, credentials, and privacy preferences. Platforms cannot revoke, censor, or override identity. *** #### **Slashing** A penalty mechanism applied to validators who misbehave, underperform, or provide incorrect validation outputs. Slashing maintains the security of the identity ecosystem. *** #### **Solana Compression** The process of storing large amounts of identity data in compressed account structures. Enables: * extremely low storage cost * high throughput * state indexing * affordable queries *** #### **State Registration** The act of registering or updating identity objects on Solana via the ZK Identity Layer. All updates propagate to the validator network. *** #### **Validator Coordination Layer** The layer responsible for: * synchronizing state * verifying proofs * ensuring consistent updates * confirming issuer authenticity * validating anchoring intervals Validators DO NOT control identity — they ensure correctness and integrity. *** #### **Validator Node** A participant in the ZKID network responsible for: * proof verification * registry synchronization * uptime * validator consensus * system fairness Validators earn rewards for ensuring liveness and for processing identity operations. *** #### **Verifiable Credentials (VCs)** Digitally signed credentials linked to a DID. ZKID supports multiple credential types: * zk-based selective disclosure * human verification * asset ownership attestations * ecosystem-specific access credentials * reputation scores *** #### **ZK-Proofs** Cryptographic proofs that allow claims to be verified without revealing underlying private data.\ Used extensively for: * identity verification * credential validation * age checks * uniqueness * membership validation *** #### **ZK Verification Layer** The privacy enforcement module of ZKID. Enables: * private verification * minimal disclosure * encrypted attributes * instant proof validation * cross-app verifiability *** #### **ZK Identity Layer** The multi-layer identity architecture combining: 1. Bitcoin anchoring 2. Solana compressed registry 3. Credential issuance 4. ZK verification 5. Validator coordination Forms the backbone of ZKID. *** #### **ZKID Validator Set** Node operators who ensure the correctness and trustlessness of ZKID. They maintain consistency, execute validation logic, and align incentives via staking. *** #### **ZK Reputation** A privacy-preserving reputation model where users can accumulate signals without exposing personal information or full history.