Cashu.spacedocs.cashu.space

Frequently Asked Questions (FAQs)

General Safety and Privacy Questions

Are there any risks when using Cashu and associated wallets and tools?

Yes. In fact, there are many risks. Make sure to understand them before putting any sats into any Cashu mint/wallet.

  • Cashu protocol, wallets, and tools are still in early development. Funds might be lost forever due to bugs in the software or the protocol.
  • Cashu wallets are ecash wallet interfaces. They are not Lightning wallets, and they do not run a Lightning node. Cashu wallets leverage the Cashu protocol to communicate with Cashu mints to integrate with Lightning. Therefore, the mint is running the Lightning infrastructure and custodies the satoshis for the mints ecash users. Users must trust the mint to redeem their ecash once they want to swap out to Lightning.
  • Ecash tokens are bearer asset tokens. This means the data that gets stored in the wallet (browser local storage) represents the actual money itself. Should the storage be wiped, funds will be lost.
  • Please take these risks seriously. Don't put any money into Cashu mints/wallets that you're not willing to lose.

How much privacy does Cashu provide?

The Cashu protocol offers a blinding mechanism to unlink the creation of an ecash token from its redemption. This gives the mint or anyone else no direct link for parties involved in a transaction. The Cashu protocol also works entirely without accounts. So theoretically it is impossible for a mint operator to determine how many users it has and who they are. There are a few things to consider though.

Privacy chokepoints:

  • Swapping in and out of the mint requires Lightning transactions. While sender privacy is pretty good on Lightning, the mint will almost certainly be able to identify a receiver that is getting paid through the mint. This still doesn't deanonymize the sender, but it does give the mint the power to censor certain payments.
  • Larger amounts most likely have less good privacy properties, due to their token denominations being rare. Cashu uses fixed (power-of-2) token denominations to create a hide-in-the-crowd effect. But the larger a token gets, the more likely it is that fewer and fewer of them exists, and at some point there is no crowd to hide anymore. If there is only one token of a specific denomination, it can always be linked back to its creation.

Inter-protocol privacy:

  • Cashu does offer decent privacy at the protocol level, but it does not take into consideration network level privacy. mints may try to collect network data such as access time, IP addresses and or other metadata. To achieve better network level privacy users should rely on tools that specialize in that, such as Tor, mixnets, VPNs etc..
  • Cashu transactions happen 'out-of-band', which shifts the responsibility to use secure channels for sending tokens. The most secure channel is to send tokens air-gapped (via QR codes), since it doesn't leave any trace of out-of-band data. If tokens need to be sent over a network, it should always be done over an end-to-end encrypted channel, preferably with self-destructing messages.

How does the Cashu ecash protocol implement privacy?

For an introduction to privacy in the Cashu protocol, see Hide Your Nuts or Blinding Custodians with Cashu.

You can also read the Cashu NUTs (Notation, Usage, Terminology).

Are there user accounts in the Cashu protocol?

No. Cashu doesn't have accounts. In fact, you don't need one. All the tokens are stored client-side, on your device.

Can the mint see my IP address when I use wallets?

If you are not using a VPN/Tor/mixnet, etc, then the Mint could see your IP address.

Are mints able to track ecash wallets by storing the payment_hash when a user receives a Lightning payment?

No, the mint does not know the Cashu ecash secret or unblinded signature (see Nut-0). Therefore, there is no linkability between a Lightning invoice and Cashu ecash.

Mints

CAUTION: Choose mints where you trust or know and trust the operator. Use small amounts or immediately redeem tokens or swap tokens to your own mint or a trusted mint.

What is a mint?

Mints are Lightning node runners that have decided to let you use their Lightning infrastructure to offer you a service. They will act as a custodian for your satoshis on the Lightning network, while they issue ecash to you, the user. You can think of it as in free banking, where the bank issues their own bank notes that is backed by gold.

Why can't I receive tokens from one mint into another mint?

Each mint has their own tokens. Therefore, you cannot receive tokens from one mint into another mint.
You can, however, use the tokens from one mint and swap them over Lightning for tokens from another mint. To transfer tokens from one mint to another, use the Multimint Swap functionality.

How do I send (swap) tokens from one mint to another?

Is there a list of mints? Which mint should I run?

Cashu is in its early development, use with small amounts.

You can see a list of some public mints on Cashumints.space or Bitcoin Mints.

Are there any test mints?

Yes, you can use:

Can I send and receive tokens to/from the same mint?

Yes, this is a common first test use case. Also, sometimes you might send a token that is not received or redeemed, and you might want to copy the token and receive it back to yourself.

How can I run my own mint?

There are several ways to run a mint, depending on your needs-see the list of Mint implementations at Awesome-Cashu.

Wallets

CAUTION: Do not open the same wallet in multiple browser tabs.

What is a token?

A "token" (also known as "ecash" or in slang "a nut") is a piece of data that consists of a blindly signed secret. It was signed by the mint with the private key for a specific amount. Therefore, a token is an IOU representation of satoshis that are custodied at the mint.

What is an ecash wallet?

An ecash wallet is a special type of wallet. Ecash wallets are always custodial, since the ecash itself has no value. Cashu ecash represents satoshis, but the keys that control the actual satoshis on-chain are at the mint. Ecash wallets come with some additional features over traditional custodial wallets, such as:

  • No accounts: Since ecash is bearer asset tokens, Cashu doesn't require accounts and balances to keep track of users' funds.

  • Enhanced privacy: Due to the fact that there are no accounts, plus the blinding mechanism for creating ecash, users inside a mint cannot be distinguished from one another.

  • Send/receive at ecash layer: Funds are sent at the ecash layer, without touching the Lightning network. This allows for out-of-band or air-gapped value transfers.

  • Stores all data locally: No data has to be stored at any servers.

I have had pending tokens for quite some time, how do I resolve this?

You can receive the tokens back to your own wallet. Check the transaction history in your wallet and locate the token to receive back into your wallet.

Do invoices generated expire?

This varies depending on the mint.

Wallet Seeds

CAUTION Your seed can only restore ecash minted or received after the seed is generated.

How do I restore?

You can restore from any wallet that supports restoring from seed. Derivation and restores are standardized. See Nut-13.

You need to save and connect to the mints you want to restore. Currently, there is no "discovery" mechanism to let a wallet know which mints are supposed to be restored.

Payment Requests

How I do I do payment requests?

In Cashu.me, to create payment requests, first enable: Settings -> Payment requests. (Optionally, you can also enable Claim automatically).

In Cashu.me, you can then press Receive -> Ecash -> Request to access the Payment Request.