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Keycard Shell screen showing the passphrase entry step during card setup.
BIP39 passphrase: what the 25th word protects, and what it doesn't
A BIP39 passphrase is an optional extra secret you add to your recovery phrase. People call it the 25th word, although it can be any string you choose. It is one of the most useful protections in self-custody and also one of the easiest ways to lose funds for good, so it is worth understanding exactly what it does before you turn it on. Understanding BIP39 BIP39 is the standard that turns a wallet's random secret into a list of words you can write down, usually 12 or 24. From those words a wa
K
Kamila
on 16 Oct 2026

All Keycard blog posts

What is a hardware wallet? How it works and what to check before you trust one
K
Kamila
on 8 Oct 2026
Hardware wallet device used to store cryptocurrency private keys offline
The Importance of Seed Phrases Explained
K
Kamila
on 29 Sept 2026
A handwritten crypto wallet recovery phrase on paper next to a hardware wallet smartcard
Reproducible builds in hardware wallets: why "same source, same binary" matters
K
Kamila
on 31 Aug 2026
Diagram showing reproducible build verification between hardware wallet source code and shipped firmware binary
Random number generation in hardware wallets: how your seed is really made
G
Guy-Louis Grau
on 19 Aug 2026
Keycard Shell hardware wallet random number generator for crypto seed security
Smartcard hardware wallets: how a secure element stores and signs
K
Kamila
on 24 Jul 2026
Smartcard hardware wallet tapped via NFC to sign a transaction using an on-card secure element chip.
Best air-gapped hardware wallets compared: QR signing, open source, and secure elements
K
Kamila
on 24 Jul 2026
Air gapped hardware wallet signing a transaction via QR code, keeping private keys isolated from any networked device.