Bunker mode and bitcoin address reuse: what bitcoiners should know

On October 7, Ethereum Foundation researcher Justin Drake asked the industry to prepare for "bunker mode": moving funds to fresh addresses in response to a possible threat to elliptic curve signatures. His concern is that advances in AI-driven math could weaken that cryptography.

His recommendation draws on a familiar bitcoin practice: avoiding address reuse.

If you have reused an address, that alone does not mean your keys are compromised or that you need to move your entire balance today.

What bunker mode asks bitcoiners to do

Drake argued that AI systems solving hard math problems could find a faster way to recover a private key from a public key. He suggested this could happen within months in a worst-case scenario.

His recommendation has two parts:

1. Move the bulk of your funds to addresses you haven't spent from.
2. Each time you spend, send what remains to a new address, which your wallet can generate from the same seed phrase.

Casa’s CEO, Nick Neuman, recommends starting with address reuse.

Your wallet can give you a fresh address for every payment

Address reuse means receiving bitcoin at the same address more than once. It usually comes from convenience: an address saved in an exchange account, a recurring withdrawal, or a QR code kept handy for future payments.

Reuse is common. In the 12 months ending October 8, 2026, 72% of new transaction outputs went to an address that had received bitcoin before, according to Bitview data. In early 2021, that share was 44%.

Suppose you buy bitcoin every month and withdraw it to the address you saved as "cold storage." The first withdrawal uses a fresh address. Every withdrawal after that reuses it.

Your wallet can generate many receiving addresses, and they all belong to the same wallet even though the characters change. Modern wallets derive these addresses from your existing keys using the HD wallet standard, so a fresh address doesn't require a new wallet or a new backup. Generating one costs nothing and moves no bitcoin.

If addresses and UTXOs are new territory, our guide to how bitcoin transactions work covers the basics.

Can someone get your private key from your bitcoin address?

There is no known practical method for deriving a properly generated Bitcoin private key from its address. Your private key authorizes spending, and your public key lets the network verify that authorization. Most bitcoin address types hide the public key, or a script containing public keys, behind a cryptographic hash until you spend.

Spending reveals that information as part of the transaction, which is normal. The concern starts when bitcoin stays at, or returns to, an address whose public keys are already visible on the blockchain. Any remaining funds still rely on those exposed public keys.

A sufficiently powerful quantum computer could derive a private key from an exposed public key. Drake's proposed AI shortcut is a separate, hypothetical route to the same result. For hash-protected address types, an address you haven't spent from does not reveal the public key onchain merely by receiving funds. Our Coldcard vulnerability guide shows how exposed public keys change the timeline when a key weakness comes to light.

Address reuse is the main reason public keys are visible today. On October 8, 2026, Bitview data showed about 7.1 million BTC, or 35% of all bitcoin, at an address with a visible public key. About 5.2 million BTC of that was at hash-protected addresses that had already been spent from. That is three times the amount held in early coins paid directly to a public key (1.7 million BTC).

A visible public key is not a compromised key. It matters only if someone finds a practical way to derive a private key from a public key.

Taproot addresses work differently

Taproot outputs include an output public key from the start. A fresh Taproot address still avoids reuse, but it doesn't hide a public key the same way. The Taproot specification explains this distinction.

Is bitcoin quantum resistant?

Bitcoin's signature cryptography is not inherently quantum resistant. But how you hold bitcoin affects its exposure to a future quantum attack. As our quantum-resilience guide explains, fresh, hash-protected addresses keep public keys unrevealed onchain until you spend, providing protection against long-exposure attacks.

Spending reveals those keys, leaving a shorter window before confirmation. Post-quantum signatures would be needed to address that remaining risk. Casa supports this preparation today through fresh receiving and change addresses that protect your public keys with hashes.

Fresh addresses protect your privacy today

Bitcoin transactions are on a public blockchain. Anyone who knows an address can see the payments it received, its spending history, and its balance.

If you share one address with a customer and later use it for exchange withdrawals, that customer can see those deposits too. Reusing the address ties those payments together in one visible history.

A fresh address for each payment avoids creating that direct link. It won't make your activity anonymous: exchanges may still know which withdrawals are yours, and later transactions can connect different addresses. Moving funds doesn't erase their history either.

Bitcoin's privacy guidance has recommended a new address for each payment for years, long before anyone said "bunker mode."

The Casa app already handles the second half of bunker mode

Casa builds these address practices into your vault’s normal operation. After each deposit, the app shows a fresh receiving address. When you send bitcoin, it automatically returns any change to a fresh address in your vault. Change is the value left over from the bitcoin outputs used in the transaction after paying the recipient and the network fee.

You don’t have to create a change address manually, set up a new wallet, or replace your backups to use fresh addresses.

A new change address doesn't mean your bitcoin left your control. Our guide to change addresses explains what you'll see when you send, including the extra confirmation some hardware devices show. Casa's bitcoin vaults use hash-protected address types, helping keep public keys unrevealed onchain until their associated funds are spent.

The app can't control which address you give an exchange or another sender. If you paste an address you've used before, a fresh address in the app won't prevent that reuse.

How to get a fresh bitcoin address and update your withdrawals

1. Open your wallet and select Receive to generate a new address. In the Casa app, each vault shows its current receiving address.
2. Verify the address using your wallet's supported verification process, such as checking it on your hardware device.
3. Give that address to your exchange or sender. Get the address directly from your wallet rather than an old note or saved QR code.

Then check the places where an old address might still live:

• Exchange address books: See whether you keep selecting the same saved destination.
• Recurring withdrawals: Review the destination set for automatic transfers.
• Saved notes and QR codes: Stop using saved copies for future deposits; get a fresh address from your wallet.
• Public payment addresses: If you receive payments or donations regularly, consider a setup that gives each payer a new address.

Many exchanges add a waiting period when you whitelist a new withdrawal address. That protection is worth keeping, so allow time for the delay before scheduling a withdrawal. Our guide to getting your bitcoin off exchanges walks through verifying a receive address.

For exchange-specific instructions, see our withdrawal guides for Coinbase, Kraken, and Binance.US.

Already reused an address? Take stock before you move anything

Start using fresh addresses for every future deposit. Then, if you want to assess existing funds, separate two situations: receiving more than once at an address, and receiving at an address you've already spent from.

Repeated deposits link your payments together even if you never spend. Spending from a hash-protected address also reveals its public keys, so any funds still at that address, including later deposits, deserve a closer look.

You don't need to work out which situation applies on your own. If you are a Casa member and have any questions or need help, you can contact our support team through the Casa app or submit your question on our website.

Moving funds costs a network fee and doesn't undo past privacy links. If you decide to move funds, take time to verify the destination before sending. Reusing an address, by itself, isn't a reason to reset your wallet or replace your keys.

Multisig and fresh addresses cover different risks

Multisig requires more than one key to authorize a transaction. In a Casa 2-of-3 vault, spending requires two of the three keys. Someone who compromises just one key cannot authorize a transaction, and losing one key still leaves two available for recovery. Keeping your keys on separate devices and in separate locations helps prevent a single incident from affecting multiple keys.

Multisig adds protection by requiring an attacker to compromise multiple keys. It does not inherently provide quantum resistance at the cryptographic level, because those keys still rely on elliptic curve cryptography.

Before your next deposit, get and verify a fresh receiving address from your wallet. Check any saved or recurring withdrawals that could still send bitcoin to an old address.

Explore Casa's multisig vaults to see how multiple keys protect your bitcoin.

Watch the full video on Bunker Mode and bitcoin address reuse here: