Most secure medium for data transfer to air gapped computers

USB can be used to transfer data from an untrusted system to an offline secure computer. But USB has firmware, usually not signed, and usually without write protection pins. Also, it has various opaque microcontrollers. Vulnerabilities such as BadUSB are used by APT to infect air gapped systems. Formatting a USB doesn’t secure it (sometimes the firmware is stored in a partition that uses a separate data channel that can be accessed only by special devices, not external OS).

What’s …

computers cybersecurity data data transfer medium