Smart Custody suggests maintaining copies of keys etched in metal. This is an excellent use case for SSKR, as it allows for the storage of key shares that don’t allow for the compromise of a key if an individual set of etchings is discovered. Ken Sedgwick demonstrated one way to do so using dogtags and the test vector.
The example uses Blockchain Commons’ default 128-bit seed, YINMN BLUE.
HEX: 59f2293a5bce7d4de59e71b4207ac5d2
BIP-39 WORDS: fly mule excess resource treat plunge nose soda reflect adult ramp planet
BYTEWORDS: hawk whiz diet fact help taco kiwi gift view noon jugs quiz crux kiln silk tied omit keno lung jade
GORDIAN ENVELOPE: See QR code, above
SEGWIT UR OUTPUT DESCRIPTOR: ur:output-descriptor/oeadisktjojeisdefzdydtaolytantjloxaxhdclaxvlcprfttldjobkredtlnhsidwybaeyjtswyandlgjnehtkdsidbkqzsrkphyfhsaaahdcxhnfgnepefxgdytryckticelyotsstoknfntavevaskiddmolsarntykbrybtjpksamtantjooeadlncsghykaeykaeykaocyhngrmuwzaycyzssajpsndifmkohy
SEGWIT TEXT OUTPUT DESCRIPTOR: wpkh([604b93f2/84'/0'/0']xpub6DVfq9VduocgjGeR69Nyr8CCi9w5gywnU7wXMYGswpHjffjcbLYNzz6G6555VDcSZLDwZPzJHJQabVWWgkpvYntpunL3UjHGrkCJ6VndbQf)#ncwysjuk
Do not use this seed to hold real monies; they could
disappear immediately!
Ken’s complete method requires the following shopping list (with two different options for the military embossing machine): https://gist.github.com/ksedgwic/d4d34cab504ac453eaf2a3656f86e2f6#file-dogtag-parts-md
The overall procedure is simple:
- Print out your SSKR as a guide.
- Optionally, print a new sheet to divide each SSKR into two parts.
- Emboss each share onto a pair of tags using the machine.
You could stop there, but Ken suggests additional security:
- Bolt each pair of tags against a blank tag to make them unreadable.
- Dip each set of bolted tags in black plasti dip to bind them together.
- Cover the edges of the dip with glitter to form a unique pattern that can’t be replicated.
- Photograph the patterns so that you can later test if the tags have been opened up.
Ken has more photographs of the entire procedure.