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Glossary

Technical terminology used throughout the Privacy Boost SDK documentation.

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Core Concepts

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Privacy Address

A 66-byte encoded string (132 hex characters) that represents a user’s receiving address in the privacy system. Contains the user’s MPK and viewing key. Safe to share publicly for receiving private transfers. Format: 0x04{mpk}{viewing_key}

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Master Public Key (MPK)

A public cryptographic key derived from the user’s wallet signature. Used to:

• Compute the user’s privacy address
• Encrypt notes for the user
• Identify the user in the privacy system

The MPK is public information and can be shared freely.

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Viewing Key

A private cryptographic key that allows decryption of incoming transactions and notes. Required to:

• View your private balance
• Decrypt transaction details
• See your transaction history

Must be kept private. Sharing the viewing key allows others to see (but not spend) your balance.

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Nullifying Key

A private cryptographic key used to spend private balance. Creates nullifiers that:

• Prove ownership of notes
• Prevent double-spending
• Authorize transfers and withdrawals

Must be kept secret. Anyone with the nullifying key can spend your private balance.

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Notes and Commitments

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Note

A cryptographic representation of a private balance. Each note contains:

• Token address: Which token this note represents
• Amount: The value of the note
• Owner MPK: Who can spend this note
• Blinding factor: Random value for cryptographic security

Notes are stored encrypted and only readable by the owner.

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Commitment

A cryptographic hash of a note, published on-chain. Commitments:

• Hide the note’s contents
• Are stored in a Merkle tree
• Enable efficient proof verification

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Nullifier

A value derived from a note and the owner’s nullifying key. When a note is spent:

• Its nullifier is published on-chain
• The nullifier is added to a spent list
• The same nullifier cannot be used twice (prevents double-spending)

Nullifiers cannot be linked back to their original commitments.

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Merkle Tree

A data structure that efficiently stores all commitments. Enables:

• Proof that a commitment exists (Merkle proof)
• Compact storage of the tree root on-chain
• Efficient verification of inclusion

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Merkle Proof

A path from a specific commitment to the Merkle tree root. Proves that a commitment exists without revealing which one.

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Operations

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Deposit (Shield)

Moving tokens from a public wallet address into a private balance:

1. Tokens are transferred to the Shield contract
2. A new note is created
3. The note’s commitment is added to the Merkle tree
4. Only the depositor can spend the new note

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Transfer (Private Send)

Sending tokens from one private balance to another:

1. Input notes are consumed (nullifiers published)
2. New output notes are created
3. Zero-knowledge proof validates the transaction
4. No public link between sender and recipient

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Withdraw (Unshield)

Moving tokens from a private balance back to a public address:

1. Input note is consumed (nullifier published)
2. Zero-knowledge proof validates ownership
3. Tokens are released from Shield contract to recipient address

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Sync (Balance Sync)

The process of querying the indexer to update local balance information:

• Fetches notes owned by your MPK
• Updates cached balance
• Retrieves new transaction history

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Cryptography

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Poseidon2

A cryptographic hash function optimized for zero-knowledge proofs. Used for:

• Note commitment generation
• Nullifier derivation
• Key derivation

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ECDH (Elliptic Curve Diffie-Hellman)

A key agreement protocol used to:

• Derive shared secrets between parties
• Enable encrypted note transmission

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AES-GCM

Symmetric encryption algorithm used to:

• Encrypt note contents
• Protect data in transit

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EIP-712

Ethereum typed data signing standard. Used for:

• Structured message signing
• Key derivation signatures
• Authentication challenges

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Zero-Knowledge Proof (ZKP)

A cryptographic proof that demonstrates knowledge of information without revealing it. In Privacy Boost:

• Proves ownership of notes
• Proves transaction validity
• Hides amounts and parties

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System Components

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Shield Contract

The on-chain smart contract that:

• Holds deposited tokens
• Stores commitment Merkle tree root
• Tracks spent nullifiers
• Verifies zero-knowledge proofs

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Indexer Service

An off-chain service that:

• Monitors blockchain events
• Maintains the full Merkle tree
• Stores encrypted notes
• Provides balance and history queries

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Prover Service

An off-chain service that:

• Generates zero-knowledge proofs
• Handles complex computation
• Submits proven transactions

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SDK Terminology

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Wallet Adapter

An interface that wraps wallet functionality:

• connect() - Establish wallet connection
• signMessage() - Sign arbitrary messages
• signTypedData() - Sign EIP-712 typed data
• sendTransaction() - Submit transactions

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Session

The authenticated state containing:

• Privacy keys (MPK, viewing key, nullifying key)
• JWT for indexer authentication
• Session expiry information

Sessions can be exported and imported for persistence.

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Resource

A namespace object in the TypeScript SDK that groups related functionality:

• sdk.auth - Authentication operations
• sdk.vault - Deposit, withdraw, transfer, balance
• sdk.contacts - Contact management
• sdk.transactions - Transaction history

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Token Handling

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Native ETH

The native currency of Ethereum. For privacy operations:

• ETH is automatically wrapped to WETH for deposits
• WETH can be optionally unwrapped on withdrawal

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WETH (Wrapped ETH)

An ERC-20 token representation of ETH. Used because:

• Privacy Boost works with ERC-20 tokens
• Enables ETH to participate in private transfers

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Token Address

The ERC-20 contract address for a token. Special values:

• 0x0000000000000000000000000000000000000000 - Native ETH
• WETH address varies by network

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Authentication

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Challenge

A random value provided by the indexer for authentication:

• Prevents replay attacks
• Has a short expiration time
• Must be signed by the wallet

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JWT (JSON Web Token)

An authentication token returned after successful login:

• Used for indexer API requests
• Contains session information
• Has an expiration time

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Error Types

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ConfigError

Invalid SDK configuration (missing URLs, invalid addresses).

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WalletError

Wallet operation failures (user rejection, signing errors).

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AuthError

Authentication failures (expired challenge, invalid signature).

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OperationError

Transaction operation failures (insufficient balance, invalid recipient).

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NetworkError

Network communication failures (timeout, server errors).

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ProofError

Zero-knowledge proof generation failures.