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scramlkb

Passphrase entry utility that aims to defeat hardware keyloggers and low-resolution spy cameras

Note that this is alpha software, things may not work as expected.

Explanation: scramlkb maps the red characters to the yellow characters displayed on the line below. The mapping is updated on each keypress by performing a Knuth (aka Fisher-Yates) shuffle of the red characters using entropy from /dev/urandom. The yellow keys stay in place, resembling the QWERTY keyboard layout.

Example: In the screenshot above, 2 would map to h; 6 -> e; k -> y. Thus, 26k would render hey. Except the entire mapping would be randomly shuffled after the first entry of 2, and again for each consecutive key press, of course.

Features

  • systemd-ask-password support, (almost working) replacement for systemd-tty-ask-password-agent (for disk passphrases on boot, ..)
  • mixed plaintext / scrambled entry, for menu systems

Similar/related tools

  • Gridfire by reid-k, written in Python
  • vkeyb, written in C
    • abandonware, you need to fix the bias error on line 22 by changing it from while(r < to while(r >= amount_of_elements)
  • gpggrid, written in C for the Tinfoil Hat Linux project (discontinued) by Shmoo

Usage

systemd "Password Agents Specification"

scramlkb partially implements the Free Desktop specification for password agents.

The strategy chosen is to aiming towards parameter compatibility with the systemd-tty-ask-password-agent (man page) for the common use cases, enabling scramlkb to be used as a drop-in replacement.

Currently implemented parameters:

./scramlkb [--watch]
--watch     Watch the `/run/systemd/ask-password/` directory for password entry requests

Password requests can be generated with sudo systemd-ask-password --no-tty "enter your password". Note that scramlkb must have permissions to read the socket (created by root in this case).

Additional references:

  • man systemd-ask-password
  • man systemd-tty-ask-password-agent

interactive pty mode

scramlkb can also be used in regular pseudo-ttys by calling the binary without the --watch parameter. This is provided to ease the use of scramlkb in scripts and day-to-day interactive input of sensitive data.

The parameters for this mode of operation are detailed below:

Usage: (./scramlkb [mode, mode, ..]) where mode is either 'c'|'u'|'p' for unscrambled lines or an integer (count of scrambled lines)
Example: (scramlkb c c 2 c) -> reads two plaintext lines, two scrambled lines, then one unscrambled line