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Materials

  • Blank business cards
  • Scratch-off security stickers
  • A sheet of small stickers (under 1 inch) to hold your codes
  • A marker or pen

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How it works

  1. Place three small stickers on each card to represent your secret codes.
  2. Scratch one card to reveal the codes and memorize them. Avoid writing them down.
  3. Cover every code with a scratch-off sticker.
  4. Make identical copies for everyone in the network and mark which network each card belongs to.
These simple supplies let you create secure cards at home. Attackers would need to know exactly which sticker sheet you used and the order of the stickers to guess your codes.

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