RCE OTPAD

Rock Castle Engineering [email protected]

The RCE One Time Pad (OTPAD) is a device designed to provide unbreakable encryption for message exchange with the following primary features:

• The One Time Pad is the only truly unbreakable cipher, when used properly messages encrypted using the RCE OTPAD can not be deciphered.
• Absolutely no logical attack vector against the device, since there is an air-gap between the OTPAD and other machines there is no way to mount a logical attack against the device.
• Very portable, small enough to fit in a pocket
• Messages and pads are easily and inexpensively exchanged using SD cards
• If a device is lost or stolen there is no risk to data, keys and messages are all stored on removable SD cards

Use Cases

Synchronize PADs

Send a message via telephone Send a message via voice recorder Send a message via SD card exchange

Firmware

• LCD Menu system
  • Incoming Messages
    • List of messages, pad index, first N chars of each message
    • scroll using up/dn buttons, select one
      • read
      • delete
      • copy to SD card #2
        • cipher text
        • clear text
  • Outgoing Messages
    • List of messages (incl "new"), pad index, first N chars
    • scroll using up/dn buttons, select one
      • read, if new message, edit it
      • send via audio
      • delete
      • copy to SD card #2
        • cipher text
        • clear text
  • PAD
    • erase
    • generate new pad
    • copy to SD card #2

Electronic Design

• Power
  • 2xAA
  • boost converter to deliver 5V
  • optional 3V DC in
• Display
  • graphical LCD
  • LED: power (bi-color, grn=good,red=low batt)
  • LED: busy (send/recv/SD copy)
  • LED: new unread message
• Input
  • Power on/off slider switch (in front of battery)
  • btn: menu up
  • btn: menu dn
  • btn: menu select
  • btn: send (send next unsent message)
  • btn: receive (receive new incoming message)
  • btn: copy PAD from SD #1 to SD #2
  • $6.99 PS2 style keyboard from tiger direct
• Core
  • PIC18
  • RTC would be nice
• Audio in
  • SFE mic
• Audio out
  • small speaker
• Storage
  • 2 SD slots
• Expansion
  • headers for PIC in-circuit programming
  • headers for ADC, DIO, GND, VCC for random number board

Storage on SD

Starting at byte 0 on teh SD card we store a block table, the first entry in the block table tells us how large the block table is. By default it is 255 * 136 bytes = 34816 bytes <8 bit entry type><64-bit start addr><64-bit end addr> entry types

• 00: block table
• 01-99: PAD
• 100: message block

Future Changes

• Improved randomicity through hardware
• serial link between devices
• firmware upgrade via SD card
• allow numeric only IO - leverage 0-9 keypad for input
• configuration/settings menu -- end README