Trezor raises passphrase limit to 128 characters after Coldcard attacks

What happened

Trezor has lifted the maximum length of its wallet passphrase from 50 to 128 characters, according to an announcement dated November 1. The change arrives through the company's October software update and needs matching device firmware, as reported by Crypto.news and Bitcoinist.

The expanded limit applies to the Trezor Model T, Safe 3, Safe 5 and Safe 7. The older Model One stays capped at 50 characters, and devices running earlier firmware keep the previous restriction until they are updated.

Trezor tied the decision to the Coldcard attacks disclosed in July, when a firmware problem caused some devices to produce recovery phrases with far less randomness than intended. Attackers could then rebuild those phrases through repeated computation and reach wallets without ever holding the physical devices.

According to Trezor, some Coldcard users avoided immediate losses because their wallets also required a passphrase that attackers could not derive from the compromised recovery information. The company said the longer limit gives experienced users one more way to protect holdings when recovery details become exposed.

Why it matters

A passphrase is an optional layer that sits on top of a wallet's recovery phrase. It generates a separate wallet with its own addresses and balances, so both the original recovery information and the exact passphrase are needed to open it. That separation is what shielded some Coldcard users: even a reconstructed recovery phrase was not enough on its own.

The episode also illustrates a limit of self-custody. Moving a recovery phrase created on a vulnerable Coldcard onto another hardware wallet does not fix the underlying weakness, per Bitcoinist; funds stay exposed until they are moved to a freshly generated wallet. Trezor has said wallets originally created on its own devices were not affected by the Coldcard flaw.

What the data shows

Coldcard's firmware generated recovery information with roughly 40 bits of effective randomness instead of the intended 128 bits, which made brute-force reconstruction feasible. During an attack on July 31, about 594 BTC, valued at $38 million at the time, was taken from roughly 500 wallets in 25 minutes. Later reporting cited in the coverage put estimated losses at about $116 million across more than 5,200 addresses by August 12.

Background

Coldcard responded to the vulnerability with updated firmware and advised affected customers to generate new recovery phrases. In August it added requirements for extra randomness in new seeds, asking users to contribute unpredictable input through keyboard activity, dice rolls or coin flips. The company cautioned that installing fixed firmware does not repair phrases created with vulnerable versions.

Trezor's passphrase announcement came shortly after a separate warning. On October 30 the company flagged possible tampering with wallets sold through former authorized reseller CryptoBilis, after an Indonesian buyer reported finding an extra circuit board inside a Safe 5. Trezor said the suspected implant could potentially collect sensitive data, including recovery phrases, and advised customers who bought through CryptoBilis from March 2026 onward to move assets to new wallets with fresh recovery phrases.

What to watch

Trezor's guidance stresses that a passphrase cannot be reset by the manufacturer. Every character must match exactly, including capitalization and spaces, and a small typing error opens a different wallet that may appear empty. Users are advised to record passphrases securely and confirm they can reopen the wallet before sending funds to it. Trezor said it had reviewed photographs and interviewed the CryptoBilis customer but had not physically examined the device, and its investigation continues with help from the Security Alliance's SEAL 911 response service.

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