With the large number of passwords required of many internet users today, managing them can be quite a challenge. Memorising a unique password for every site is impossible, forcing password reuse and so creating vulnerability should any one site be compromised or else requiring the use of a 'password notebook' to write them down and introducing the risk of loss or theft.
This is my solution. It's a password management tool, implemented in hardware for perfect security - no radio links. As a password tool, it functions by simply running whatever sequence is entered on the keypad through an SHA1 hash and displaying the truncated result in a printable form. Operation is by entering a single secret prefix, followed by the name of a site (using the telephone-letters system). This provides a unique password for use on every site or service, while requiring the operator memorise only the prefix sequence. The device itsself contains no presistant storage and so is of no concern if stolen, may be used by many individuals (using different prefix codes) and, if lost, can be easily rebuilt or simulated in software.
The device is constructed using an arduino nano controller, a matrix keypad and an SPI-interfaced display. It can be powered by USB, or by a li-ion cell and boost converter. Additionally it can easily include auxilary functions with the addition of very few parts - serial line monitor, voltmeter, ammeter or infra-red remote control mimick would all be fairly easy to include.
I'm making the source for the arduino available, should you wish to build your own. It includes the SHA1 and display library files, but not the documentation or examples that come with them, just the essentials for compiling. Pin assignments are documented in the source.