The present invention is notably directed to a user trusted device (10), comprising: a connection interface (12) enabling connection (S2) with a computer (101); and a persistent memory (14) storing modules (15, 16, 17), which are configured, upon connection of the user trusted device (10) with said computer (101) via said connection interface (12), to: enable said computer (101) to start booting (S3, S3a) from the user trusted device (10); map (S6) firmware data to a code, the firmware data comprising program code of an initialization firmware and/or data accessible by the initialization firmware (122) of the computer while starting to boot; attest (S7-S12) trustworthiness of the code; and enable (S14) said computer (101) to complete booting from the user trusted device (10) if the code is attested. The present invention is further directed to related systems and methods.