Frequently Asked Questions

Some of the most frequently asked questions about Fluidkey.

What can Fluidkey be used for?

Fluidkey gives users the ability to receive payments while protecting their privacy.

We’ve built Fluidkey to be flexible and usable as a day-to-day privacy preserving wallet. This opens up a wide range of use cases. We have listed a few below:

  • Managing your personal funds

  • Receiving money from friends and family

  • Receiving your salary or freelance payments

  • Receiving product or service payments from clients

  • Receiving funding from investors

  • Crowdfunding or donations

Which wallets is Fluidkey compatible with?

Fluidkey is compatible with a wide range of wallets. Here is a non-comprehensive list of some of the wallets we support:

  • Metamask

  • Coinbase Wallet

  • Rainbow

  • Dawn

  • Any WalletConnect-compatible EOA or MPC wallet

You can also connect to Fluidkey with your Farcaster, Google, or email account.

Which chains is Fluidkey available on?

Fluidkey is currently in beta on Base, Optimism, Arbitrum, Polygon, and Ethereum mainnet.

We don't recommend using Fluidkey on Ethereum mainnet for payments below $10,000 due to high gas fees.

What makes Fluidkey unique in managing wallet privacy?

On a public blockchain like Ethereum, using a new address for every transaction is an effective strategy to maintain privacy. Juggling multiple addresses can however quickly become overwhelming. With Fluidkey, you have the privacy of a new address for every transaction without the headaches of managing all these addresses.

Fluidkey creates a new privacy-protecting smart account for every payment you receive thanks to the use of stealth addresses. We then bring all of these smart accounts together in a unified dashboard, giving you the experience and ease of managing a single wallet. For more details on how stealth addresses and Fluidkey work under the hood, check out How does Fluidkey work? below.

How does Fluidkey work?

To explain how stealth addresses and Fluidkey work, we'll follow Alice, a Fluidkey user. Fluidkey helps Alice increase privacy for both herself and anyone sending money to her. Let's see how.

Overview

When Alice's friend, Bob, sends money to her, outsiders only see that Bob sent money to an address that has never been used before. They can't determine the recipient or the reason for the payment. Alice can control her funds without revealing her identity.

Introducing Stealth Addresses

When Alice signs up to Fluidkey, the system generates private viewing- and spending keys, as well as a stealth meta-address.

Let’s focus on the stealth meta-address for now. Think of this as a digital instruction manual to generate a unique, one-time use stealth address on Alice's behalf, without her having to do anything.

A stealth address is like an anonymous mailbox where:

  • Bob can send his payment

  • Only Alice can access and control the funds sent to it

  • No one else can link this address back to Alice

To the external observer, a stealth address just looks like any other address on the blockchain.

Automatic Generation of Stealth Addresses

Every time Bob clicks on Alice’s Fluidkey-enabled payment link, a new stealth address is automatically predicted, thanks to her stealth meta-address. When Bob sends his payment to this new address via Fluidkey, a smart account that only Alice can control but cannot be linked to Alice by an external observer is created at the predicted address.

Notification and Control: Viewing and Spending Keys

As mentioned earlier, Alice has two special keys:

  • A private viewing key which allows Alice to scan the blockchain for payments meant for her. Since scanning for payments on her own is tedious, she allows Fluidkey to use this key to notify her of incoming payments in real time.

  • A private spending key which is solely for Alice to control her funds. Fluidkey never asks for this key and can't access Alice’s money.

Managing Multiple Payments

With many payments coming in, managing multiple stealth addresses could get complicated. Fluidkey simplifies this by displaying all of Alice's funds in a unified dashboard, making it feel like a regular crypto wallet.

Spending Funds

When Alice wants to send money, Fluidkey automatically checks which of her stealth addresses has the right amount. If none do, it finds the best combination of addresses to fulfill the payment. For Alice, the experience remains simple, she approves the transaction just as she would in any other wallet. For the recipient of Alice’s payment the experience also stays simple, as she sees a single payment coming in.

Technical deep-dive

If you are interested in learning more about stealth addresses and the mathematical principles they are based on, we recommend:

How private is Fluidkey?

Fluidkey uses stealth addresses to protect your privacy. Stealth addresses provide unlinkability, meaning an external observer can’t link a receiver to a payment. This provides sufficient privacy for many use cases and enables a seamless user experience.

Stealth addresses also don't mix your funds with other users’ funds. This means that with Fluidkey there is no risk of mixing your funds with illicit funds.

However, stealth addresses do not break traceability. With stealth addresses, it is straightforward to trace back the history of transactions that led the funds to the stealth address in which they are now.

This can be an advantage, as it makes it easy for Fluidkey users to disclose the origin of their funds to trusted third parties like tax authorities or auditors.

Who can view my transactions?

With a regular wallet, anyone that has ever seen your address (e.g. by sending or receiving a payment, or by looking up your ENS) can see the entire transaction history and all assets stored at this address.

With the Fluidkey interface, only you and Fluidkey can see all transactions and assets. A new address is generated for every incoming payment.

Fluidkey needs view access in order to:

  • Generate stealth accounts on your behalf when your ENS is called

  • Index transactions by scanning the blockchain and displaying them in your dashboard

Here's an example of who can see what. Let's assume you receive four payments to your Fluidkey account: $10, $100, $1,000, and $10,000.

For each of these payments, the sender only knows of the address they sent the funds to at the moment of sending. E.g. the sender of the $10 payment wouldn't know about the $100, $1,000, and $10,000 payments.

An external observer would only be able to see that funds were sent to four new addresses, but wouldn't be able to link these addresses together or link them to you.

Now let's say you need to make a payment of $800 and another of $250. Fluidkey would automatically select the addresses to fulfill these payments with the goal of protecting your privacy.

For the $800 payment, this would mean sending funds out of the address containing $1,000. This means that only the sender of the $1,000 and the recipient of the $800 would be able to tie these two transactions to you.

For the $250 payment, Fluidkey would select the remaining $200 from the $800 address and $50 from the $100 address. This means that the senders of the $100 & $1,000 and the recipients of the $800 & $250 would be able to tie these four transactions to you.

None of them would be aware of the $10 and $10,000 payments and external observers would still not be able to link any of these to you.

Can I access my funds without Fluidkey?

Yes, Fluidkey is fully self-custodial, which means that only you can access your funds with your private keys and you can do so even without Fluidkey.

The Fluidkey Stealth Account Kit is an open source library containing all of the core cryptography required to access your stealth accounts.

Multiple independent recovery interfaces have been built on top of this library, making it simple to recover funds without relying on the Fluidkey interface and without being a developer.

We have hosted one of these interfaces, SARA, at recovery.fluidkey.com.

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