Modes of Operation

Proofs & whitelisting.

HollowDB has two modus operandi: proofs and whitelisting; both can be enabled together, or separately.

Mode	Put	Update	Remove	Get
Proofs	-	Zero-Knowledge Proof	Zero-Knowledge Proof	-
Whitelisting	PUT whitelist	UPDATE whitelist	UPDATE whitelist	-

Using Proofs

Using zero-knowledge proofs gives full control to the users on updating the value at their key. When proofs are enabled:

• Anyone can read and put.

• To update or remove a value at some key, user must provide a zero-knowledge proof (ZKP) of preimage knowledge of that key.

HollowDB makes use of a circuit that we call "HollowDB Authentication" circuit, to which you can find more information at:

HollowDB Authentication

You can enable or disable proof checking with the following Admin command:

const isProofRequired = true; // or false
await admin.updateProofRequirement("auth", isProofRequired);

If you are deploying your own contract, you must also provide the verification key that the proof verifier will use. You can find HollowDB's keys here. You can either provide the key in the initial state, or use the Admin to update the verification key at a later time:

await admin.updateVerificationKey("auth", newVerificationKey);

Using Whitelisting

Whitelisting is an alternative authorization mechanism that can be used within HollowDB. It can provide a fine-grained control over who can put, update, or remove a value to the database. When whitelisting is enabled:

• Anyone can read.

• To put, the user must have been put-whitelisted by the contract owner.

• To update or remove, the user must have been update-whitelisted by the contract owner.

There is a separate whitelist for put and update/remove. You can enable/disable them with the Admin:

const isPutWhitelistRequired = true; // or false
const isUpdateWhitelistRequired = true; // or false
await admin.updateWhitelistRequirement('put', isPutWhitelistRequired);
await admin.updateWhitelistRequirement('update', isUpdateWhitelistRequired);

You can add & remove users from the whitelist using the Admin:

const whitelistType = "put"; // or "update"

// add some users
const addressesToAdd = [address1, address2 /*, ... */];
await admin.updateWhitelist(addressesToAdd, whitelistType, 'add');

// remove some users
const addressesToRemove = [address3, address4 /*, ... */];
await admin.updateWhitelist(addressesToRemove, whitelistType, 'remove');