Universal Serial Bus (USB)

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Nearly all computers and other portable devices now support a single Universal Serial Bus (USB) for both data and power.


  • Legacy serial ports on computers were slow speed and specific to a particular function, like: keyboard, mouse, audio in, audio out, serial RS232 port or printer port.
  • Now when a device is connected to a computer USB port is must identify itself so that the computer can recognize that device and ensure it has the correct device driver installed.
  • The smart card had a similar serial port with similar functionality. Since there were multiple card types, the card will "Answer to Reset (ATR)" with a code identifying it.[1]
  • New Security Tokens for User Identifiers and Attributes are built to connect directly to the USB port and provide similar locator codes.


  • Since the first Smart Card was issued, portable identification devices have needed to issue Locator Codes of some sort which allow the attachment to acquire a software driver to support the card.
  • Smart cards have worked well for controlled environments like: governments, colleges and corporations. Consumers have never been willing to tolerate the complexity of the card and the X.509 Certificate they needed.
  • The first attempt was to add a card reader to convert from Smart Card format to USB, but the added hardware was enough to impede consumer adoption.
  • Even if the USB device worked, it was not recognized by the User Agent (browser) from companies like Microsoft, Apple and Google.


  • The first solution was a browser add-on from Google that would allow security keys that were plugged into the computer to be queried by the browser and perform a function just like "Answer to Reset".
  • A similar solution for Smart Phones include NFC and Bluetooth, explained elsewhere, none of which provide a secure physical connection.
  • An alternate solution for devices with Trusted Execution Environments is to place the User Identifier and Attributes into a well-secured location within the device itself.

USB Security Tokens


  1. eft lab, Smart Cards - Answer To Reset (ATR). https://www.eftlab.co.uk/index.php/site-map/our-articles/169-demystifying-atr-answer-to-reset