Signed firmware is device software that carries a cryptographic signature from the vendor. When the device boots or updates, it checks that signature before accepting the code. If the signature is missing, invalid, or from an untrusted key, the device rejects the firmware.
This matters because firmware runs below the operating system and often controls security-critical functions such as key storage, boot checks, and hardware access. In products like hardware wallets, signed firmware helps prevent attackers from loading modified code that could steal secrets, disable protections, or hide malicious behavior. Defenders use it as part of secure boot and update validation, while attackers may try to bypass it by exploiting a signing key, tricking users into installing fake updates, or attacking the supply chain. Signed firmware does not make a device invulnerable, but it raises the bar by tying code acceptance to a trusted vendor identity.