TmpUsb usage

 

When you plug TmpUsb in for the first time, it will start in “Not Armed” mode, as visible from drive’s label. Visually you would recognize this mode by the fact that LED is on. At that time you can freely use it as you would any standard USB drive. At this time you would copy your encryption keys to it and change its label to “Arm” and unplug it.

On next plug-in (might be on another computer) LED will turn off and drive will be considered armed. In this state drive will still behave as a standard USB drive but only while it has power. If there is a power loss longer than approximately three seconds (configurable, to allow for computer reset) drive will self-erase and return to an empty state.

LED

There is a single LED on a drive. If it is on, drive hasn’t been armed and it is safe to unplug it without going into risk of losing data to self-erase. Once drive is armed, LED will turn off.

Upon self-erase, device will quickly blink three times. If self erasure was due to validation error (i.e. drive content was corrupted) it will blink five times.

Commands

All commands are entered by changing drive label. Casing is not important.

Arm

Gives command to TmpUsb to be “armed” on next plugin. This fits scenario where user prepares encryption keys on one computer, arms TmpUsb and then plugs it in on another computer. Only once TmpUsb has been plugged in for a second time, it is considered armed and any further label changes won’t change that status. In this mode TmpUsb will tolerate short power loss (approximate three seconds) but anything longer will trigger self-erase.

ArmMax

As with Arm command, this will cause TmpUsb to be armed on next plugin. However, unlike with Arm command, any power failure will trigger self-erasure regardless of power-loss duration. On most computers this means that self-erasure will be also triggered by a simple reset.

Armed

Immediately “arms” TmpUsb without need to wait until next plugin. This is useful in case where preparation of encryption keys is done on same computer where those keys are to be used. It is just a shortcut that skips need for unplug-plug that Arm command needs. Once armed, LED will be turned off and status will remain armed even if drive label gets futher changes.

Calibrate

If standard power-loss buffer duration (approximately three seconds) is not satisfactory, user can change drive label to “Calibrate” and unplug the drive. Once drive is plugged back in, it will determine duration it was plugged out for and use that as a new default. Notice that drive will be erased and its label will say what is raw ADC value for given time. Do try to avoid values less than 3. Due to nature of time keeping via the capacitor, values are really rough and they are unusable beyond 10 seconds. Value determined by this procedure will be used until either ArmMax or Reset are given. At that time TmpUsb will revert to default three seconds.

Forgetful

Drive will reset itself upon each plugin. Useful if you want to use it for temporary key export. Not your everyday setting.

Reset

On next plug-in TmpUsb will perform self-erasure together with reset of all settings.

ReadOnly

This command works only once drive has been armed. It will cause device to go into read-only mode immediately. No further writes to device will be possible until device is completely cleared (e.g. due to power loss). Upon going into read-only mode, device will quickly reset so that operating system can notice its read-only status. Self-reset will be omitted if ArmMax was used for arming.

Batch devices don’t support this command, Dave. You need to update the firmware.


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