How to Use a Hardware Wallet Passphrase Safely: Lessons From Coldcard and Trezor’s New 128-Character Limit

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Trezor has raised the maximum length of its wallet passphrases from 50 to 128 characters, and the company points directly to this summer’s Coldcard thefts as the reason the feature matters. That makes this a good moment to look at one of the most misunderstood settings on a hardware wallet: what a passphrase does, when it is worth the risk, and how to set one up without locking yourself out of your own coins.

The short version: a passphrase can be a real second lock, but only if it is truly random and you can reliably reproduce it. A longer limit does not make anyone safer on its own.

What changed at Trezor

Trezor announced the change on November 1 in a post about its October Suite update. According to reporting by Unchained, the details are:

• Supported devices: Model T, Safe 3, Safe 5 and Safe 7. The older Model One stays at 50 characters.
• What you need: the newest Trezor Suite app plus a device firmware update. Core firmware 2.13.0 lists the new ceiling, and devices on older firmware keep the 50-character cap.
• Rollout: release notes list Suite 26.10.3 on desktop and 26.10.2 on mobile, and updates arrive in stages.

Trezor’s own post describes passphrases as an advanced feature and warns that a mistyped or forgotten one can cost you your funds.

What a passphrase actually does

Under the BIP-39 standard, your recovery words are run through a key-derivation function (PBKDF2 with HMAC-SHA512, 2,048 iterations) together with an optional passphrase. If you never set one, an empty value is used. Three consequences follow:

• Each passphrase opens a separate wallet. Different passphrase, different addresses, different balance. Your standard wallet is still there, unchanged.
• There is no such thing as a wrong passphrase. The standard says every passphrase produces a valid seed. Type one letter wrong and your device will not show an error. It will open a new, empty wallet.
• The passphrase is not stored on the device. Trezor says nobody can recover it for you, including its support team. Lose it and that wallet is gone for good, even if you still have all your recovery words.

It is also not your device PIN. Coinkite’s advisory says so explicitly: a PIN protects a physical device, while a passphrase changes the keys themselves.

Why the Coldcard thefts brought this back into focus

On July 30, Coinkite published an advisory about a firmware bug that weakened seed generation on Coldcard wallets. Seeds from affected Mk4, Mk5 and Q firmware had about 72 bits of entropy instead of the expected 128, and the older Mk2 and Mk3 line was described as more severe. The company said the devices were not hacked or remotely accessed. Attackers regenerated the weak seeds offline and used the resulting keys to take funds.

Galaxy Research’s high-confidence estimate, as reported by MLQ, was 1,596 BTC taken from about 7,300 addresses, worth more than $100 million at the time. A broader count that includes suspected activity reached about 2,055 BTC.

This is where the passphrase comes in. An attacker who rebuilt a weak seed still needed the passphrase to reach any wallet behind it. Trezor says users with strong, unique passphrases were protected during the first wave, which gave them time to move their coins.

Two caveats keep that from being a happy ending. First, Coinkite still tells those users to migrate as soon as practical, because a passphrase does not repair a weak seed. Second, it warns that short, common, patterned, quoted or reused passphrases may be guessable. Unchained also relayed a report from an X account, BTC Sessions, of what it called the first confirmed loss involving a short two-word passphrase. That report is unverified, but it fits the warning.

What this means for you: length is not strength

Here is the part most headlines skip. Trezor itself cautions that “length alone doesn’t guarantee entropy.” Its earlier guidance notes that cracking tools work through dictionary words, leaked passwords and patterns. A 120-character song lyric could be weaker than six random words, because the lyric is something a program can try.

The number that matters is how much true randomness went in. A simple way to get it is the diceware method using the Electronic Frontier Foundation’s long wordlist, which has 7,776 words. Each word chosen by rolling dice adds about 12.9 bits, so six words give roughly 77.5 bits. For scale, that is slightly more than the roughly 72 bits Coinkite estimated for the flawed Mk4, Mk5 and Q seeds, and it would be stacked on top of your seed rather than replacing it.

So who should actually use one?

• Probably yes: you hold a meaningful amount in self-custody, you are worried about someone finding your recovery words, and you are comfortable maintaining a second secret.
• Probably not yet: you are new to self-custody, your backups are not organized, or your heirs would have no way to find the passphrase. For many people, losing access is a bigger risk than theft. Our crypto inheritance guide covers how to plan for that.
• Consider an alternative: if you want protection against a single device or seed failing, a 2-of-3 multisig setup solves that problem in a different way.

How to set up a passphrase safely: step by step

1. Update first. Install current firmware and the official wallet app. Download only from the manufacturer’s site. If you own a Coldcard, follow Coinkite’s advisory before generating anything new.
2. Generate it randomly. Roll a set of precision dice (check current price on Amazon) and pick at least six words from the EFF list. Do not use quotes, names, dates or anything you have used elsewhere.
3. Stick to simple characters. Trezor Suite’s guide says passphrases there support the standard ASCII set. Lowercase words separated by single spaces are easier to retype. Capitalization and spaces both count, so decide on one format and write it down exactly.
4. Enter it on the device if you can. Trezor says the Safe 7, Safe 5 and Model T support on-device entry by touchscreen, which keeps the passphrase off your computer. Trezor also warns against letting a browser autofill the passphrase field.
5. Back it up on its own. Trezor advises writing it on paper, making no digital copies and keeping it apart from your recovery phrase and your device. For durability, stamp it on a separate steel backup such as the Billfodl (check current price on Amazon) and store it in a different place, for example a SentrySafe fireproof box (check current price on Amazon). Our free Seed Phrase Backup Checklist can help you confirm nothing was missed.
6. Write down the first receive address. Because a typo opens a different empty wallet with no warning, this address is how you know you are in the right one.
7. Test before you trust it. Close the wallet, re-enter the passphrase from your backup and confirm the same address appears. Then send a small amount, and recover it before moving anything larger.
8. Do a yearly check. Re-enter the passphrase from your written backup once a year, so you find out about a smudged or misread copy while you can still fix it.

Watch out for the portability trap

Long passphrases have a cost that is easy to miss. Limits vary by device: the Model One stays at 50 characters and Ledger’s academy states a 100-character maximum, while BIP-39 itself sets no limit. A 110-character passphrase could leave you unable to enter it on another brand’s device if your Trezor breaks. Six to eight random words fit well inside 100 characters, which makes them a better choice than filling the full 128. If you might ever rely on a 50-character device, count the characters, since a long six-word phrase can run over.

Ledger’s setup differs too: you can attach the passphrase to a secondary PIN or enter it temporarily. With a secondary PIN, Ledger warns that three wrong attempts reset the device.

What a passphrase will not fix

• A weak seed. It buys time, but you should still migrate. Unchained also notes that a wallet first created on a Coldcard and later restored on a Trezor should be moved, since restoring does not change the seed.
• A tampered device. Trezor told buyers who purchased from the former reseller CryptoBilis since March 2026 to move funds to a new wallet after a customer reported a suspected implant, though Trezor had not examined that device and said it had no reports of stolen funds. Where you buy still matters, as we explained in how to buy a hardware wallet safely.
• Coins on an exchange. A passphrase only protects wallets you control, and has no bearing on funds held on a platform. The $6.3 billion Binance hack shows why that matters. Our Exchange vs Hot Wallet vs Cold Wallet checker can help you decide where your holdings belong.

If you are shopping for a device that supports both the new limit and on-device entry, the Trezor Safe 5 (check current price on Amazon) qualifies. Confirm the seller is the manufacturer’s official storefront before you buy, and always generate a new seed on arrival.

What to watch next

• Other wallet makers. The coverage we reviewed did not report a matching change elsewhere, so watch for updated limits or guidance from rivals.
• The CryptoBilis report. Trezor had not yet examined the reported device, so a forensic finding would clarify the risk.

Frequently asked questions

Is a passphrase the same as a 25th word?

People often call it that, but it does not have to be one word and is not part of the recovery phrase. It can be a word or a full sentence, and it is entered separately, so it should be backed up separately too.

What happens if I type my passphrase wrong?

You will see no error. The device opens a different, valid, empty wallet. Noting your first receive address helps you spot this straight away.

How long should a crypto wallet passphrase be?

Focus on randomness rather than character count. Six or more words chosen by dice from the EFF list is a practical target, since it provides roughly 77.5 bits or more.

Does a passphrase protect me if my seed was affected by the Coldcard flaw?

A strong, unique passphrase is an independent barrier, according to Coinkite, but it does not repair the seed. The company’s advice is still to migrate to a newly generated seed as soon as practical.

This article is for informational purposes only and does not constitute financial advice.