Arbitrum Adds NullMask Privacy for Transfers and Balances

By Nathan Brooks

Arbitrum has added NullMask to support three workflows without identity disclosure: sending funds, making deposits and checking balances. The Ethereum layer-2 network is adding the feature alongside Fhenix’s Dual Mode, a transaction-level control that lets users switch from public to private mode.

What does NullMask change for users?

Arbitrum describes the result as allowing users to send funds, make deposits and check balances “without disclosing their identities.” The feature covers three actions that sit on either side of a transfer: checking a balance, depositing funds and sending funds.

That distinction matters for users evaluating privacy tools. A transfer-only control can leave account discovery and funding steps outside the private workflow. NullMask’s stated scope includes those adjacent functions, so a user could conduct the described operations without disclosing identity through the feature.

The claim remains narrower than a general guarantee of anonymity. The source does not say NullMask conceals addresses, counterparties, amounts or network metadata, and it does not specify what information the feature still collects or retains. Users should not equate identity non-disclosure with complete transaction invisibility.

A different privacy model from Dual Mode

Arbitrum added NullMask alongside Fhenix’s mainnet launch on Arbitrum. That launch brought Dual Mode, which lets users switch a transaction from public mode to private mode. The available description therefore points to two different operating concepts, not one clearly unified privacy mechanism.

Dual Mode gives the user a visibility choice at the transaction level. NullMask is described at the workflow level, covering deposits, balance checks and transfers without identity disclosure. The available description does not state whether the two options share underlying technology, tooling or transaction paths, so they should not be presented as interchangeable.

For wallets, interfaces and applications, that difference creates a concrete integration question: which private functions will be available through each route, and whether users can move between public and private operation. The available description does not provide enough technical information to answer either point.

Implementation questions remain

The source supports the existence and stated scope of NullMask, but leaves implementation questions open. Before treating the feature as production-ready, teams should establish:

• Whether the deployment is available to every Arbitrum user or remains limited by interface, contract or geography.
• Which assets and deposit paths support the three functions.
• How fees, transaction data, addresses and counterparties are handled.
• Whether the feature has undergone independent security review.
• How users recover funds if a deposit or private transfer fails.

These are not disclosures from the announcement; they are due-diligence items created by what it leaves unsaid.

A segmented privacy stack

Arbitrum now has two named privacy options in its product stack: NullMask’s three-function workflow and Fhenix’s Dual Mode transaction switch. That does not establish a shared standard, guaranteed interoperability or broad adoption. It does establish a broader choice for users and integrators than either mechanism would offer alone.

For the network, the operational consequence is a more segmented privacy stack. One layer addresses identity disclosure around balances, deposits and transfers; the other addresses public versus private transaction visibility. Success will depend on whether those functions become usable together without leaving identity-disclosing balance or deposit steps outside the private workflow.

The forward-looking market-structure change to watch is consolidation around a common privacy interface across those routes. No timetable, fee schedule or technical specification appears in the source, so implementation evidence, rather than announcement timing, will determine whether Arbitrum’s privacy options become a coherent market structure.