Secure iButton

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Revision as of 14:02, 29 December 2012 by Bertrik Sikken (Talk | contribs)

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Project Secure iButton
Status Initializing
Contact User:Bertrik Sikken
Last Update 2012-12-29

This project is about investigating and using the secure features of the iButton that people currently use for physical access to RevSpace.

Planned project phases are:

  • phase 1: investigate possbilities of the iButton and experiment with it
  • phase 2: write software for the iButton functionality and package it into a library
  • phase 3: apply knowledge and software for application within RevSpace

iButton investigation

The iButton used at RevSpace is the DS1961, with the following features:

  • 4 pages of 32-byte user data each
  • an 8-byte write-only "secret"
  • SHA-1 algorithm that can calculate a hash over a 32-byte user data page, the 8-byte secret, a 3-byte "challenge" and the unique iButton id.

Basically authentication could work like this:

  • (the secret key has been installed on the iButton previously)
  • user presents iButton to the reader
  • reader reads the unique iButton id
  • reader generates a random number and uses this as the challenge to read a 32-byte user page
  • iButton sends the user page, followed by the SHA-1 hash
  • reader also calculates SHA-1 hash and compares it with the iButton hash
  • if the hash matches, the user data can be considered as authentic and the reader can interpret the user data as a "deelnemer id" (or something) for example.

Bus pirate experimentation

Investigation of the DS1961-specific commands can be done with a Bus Pirate. A bus pirate speaks the 1-wire protocol that any iButton-like device uses.

Examples of commands:

  • Initialise the bus pirate
  # (reset the bus pirate)
  M (select mode)
  2 (1-wire mode)
  W (enable power)

DS1961 library

This library provides an API for the DS1961 specific functions. It will be targeted at the Arduino microcontroller, to run on top of the existing 1-wire library.


We could apply this to improve the security of RevSpace access for example. to be discussed.