“Ovrdrive is a purpose built security focused usb drive. If the user doesn’t lick their fingers while inserting the drive it will appear completely blank. It is entirely open source and all the tools used to build it are open source. There is a blog series listed below with more information for the curious.
ATTINY24A-CCUR - BGA version
ATTINY24-20PU - DIP version
K9gag08u0e-Scb0 - NAND Flash
SM3255AA - What dmesg thinks the chip is
SM3257EN - Part number on the chip
SM3257ENAA - Reported by SMI Mass Production Tool