VFS (encryption)

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mongoose-os-libs/vfs-dev-encr mgos_vfs_dev_encr.h    

Overview

  • AES-128/192/256 are supported (algo: AES-nnn parameter, default is AES-128).

  • Reads and writes are encrypted, erases are passed through as is.

  • Encryption is performed in ECB mode, key is XORed with offset.

  • Reads and writes must be aligned to 16-byte boundaries.

  • Writes will be padded to 16 byte block size, so partial writes will only work for last plain-text block.

    Hint: If you want an encrypted filesystem, LFS will work just fine with this method while SPIFFS will not.

Key source

Key can be supplied directly (as the key option) but a better approach is to use a key device to obtain the key when required.

Key device can be any other VFS device that supports reads. It can be an existing device (key_dev: name) or created in-situ (key_dev_type + key_dev_opts).

Hint: To read key from RAM, use the vfs-dev-ram.

Hint 2: Want to generate your own key? Create your own VFS device. Don't worry about methods other than read.

Example

Options for encrypting extf0 with AES-256 with key from STM32 OTP area (536836096 = 0x1fff7800).

 {"dev": "extf0", "algo": "AES-256", "key_dev_type": "RAM", "key_dev_opts": {"addr": 536836096, "size": 32}}

Don't forget to add vfs-dev-ram to libs.


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