#### How to recover your secret

Find the three holes in the corners, then flip and/or rotate the card until they are positioned as upper-left corner, bottom-left corner, and bottom-right corner.

Download and print the template, and align it to match the card.

Alternatively, imagine (or draw with a pencil) two grids of 8x8 (one for each key word), then another two 1x8 (one for each CRC word).

Use the `reset` button to clear the page checkboxes.

Click each key checkbox that matches a hole on your card.

Check that the CRC checkboxes pattern matches the one on your card.

Now, depending on what you've used when creating the backup, either use the `key txt`, `key hex`, or `key b10` input boxes to recover your secret.

#### How to backup your secret

(1) Selecting your secret

Recommended, if you don't yet have a secret to backup, then it's best to just generate a truly random 128 bit number, represent it in hexadecimal, and use the `key hex` input box. (Just ignore the `key b10` and `key txt` inputs.)

If you already have a secret to backup, use the `key txt` input box, and hopefully it fits into 128 bits and it won't be truncated (else a warning message would be given). (The code uses a few heuristics to choose an optimal representation, depending on which characters you are actually using.)

(2) Preparing to punch holes

Download and print the template, and use it as a guide for the hole punching that follows.

Use an aluminium, or stainless steel, sheet as the physical medium. (Although, cardboard, wood planks, or other material could be used.)

Use a center punch tool to mark where the holes are to be drilled. Use a small drill bit (1mm) to drill the holes.

(3) Punching holes

* tape the template to the aluminium sheet;

* use the punch tool to mark where the holes are to be drilled;

* mark the three (green) corners (upper-left, bottom-left, bottom-right); (these are to be used as alignment markers on recovery, to make sure the card isn't flipped;)

* mark the key (blue) holes and the CRC (orange) holes as seen on the page;

* count and check if you've marked all the proper holes;

* drill the holes you've just marked;

* count and check again that you've drilled all the proper holes;

* cut the aluminium sheet; (there are 4 dots in the corners to help place a ruler, then using a cutter, tracing it many times on aluminium, one can easily cut the sheet;)

* polish the sheet with sandpaper;

(4) Check the secret recovery

Follow the recovery section to make sure you've punched the proper holes, and to make sure you know how to recover your secret.

hole punching template (PDF A4)

github.com/volution/punchcard-key-backup