Revocation Keys

Revocation keys enable retrospective taint recovery — a mechanism unique to Nullmask that addresses the problem of funds being tainted after they've entered the privacy pool.

The Problem

In existing privacy protocols (e.g., Railgun), once tainted funds enter the pool, there is no way for users to disassociate from them. The entire pool remains tainted indefinitely.

Nullmask's Solution

The guard publishes a revocation key pair with each approved deposit:

• The public key (revocationPublicKeyX, revocationPublicKeyY) is published in the Deposit event

• The public key hash is used as the value_trapdoor in the deposit note commitment

Each Nullmask note includes encrypted information about the deposits that funded it.

Retrospective Taint Recovery

If a deposit is flagged as tainted after approval:

1. The guard publishes the secret key corresponding to the revocation public key

2. Each protocol participant can use this key to:

   • Determine if their notes were funded by the tainted deposit

   • If not tainted: generate a proof of disassociation

   • If tainted: verifiably clean the rest of their untainted balance

Comparison

Protocol	Retrospective Taint Handling
Railgun	No mechanism — pool remains tainted indefinitely
Privacy Pools	Exclusion proofs + retrospective compliance, but no shielded transfers available
Nullmask	Revocation keys enable targeted taint recovery

This mechanism ensures that even if some tainted funds enter the pool, individual users can prove their funds are clean, and the pool can recover from tainted deposits.