6

After creating a mnemonic seed for offline cold storage with the guide described here how can I safely encrypt it in pieces with the help of Shamir's Secret Sharing?

What are some other viable alternatives to secure my wallet offline in pieces, none of which can recreate my account on its own?

11

There is no support for SSS in simplewallet. This would require some amount of new modexp code to be added (unless a variant of it can be made using EC cryptography, but I'm not aware of any).

So the best you can do is use a standalone SSS tool such as ssss (see http://point-at-infinity.org/ssss/). It may already be in your distribution's packages.

Example, with the words "shamir secret sharing":

$ ssss-split -t 2 -n 3
Generating shares using a (2,3) scheme with dynamic security level.
Enter the secret, at most 128 ASCII characters: Using a 168 bit security level.
1-b52fb8b2fc481023c708c25c798a45e349951e9af8
2-6191ac079ef7624a72ffce0da2372d6a24fe2e530c
3-d2045f94bf624c6d1e52ca3d14a3f512ffd8c19459

and:

$ ssss-combine -t 2
Enter 2 shares separated by newlines:
Share [1/2]: 2-6191ac079ef7624a72ffce0da2372d6a24fe2e530c
Share [2/2]: 3-d2045f94bf624c6d1e52ca3d14a3f512ffd8c19459
Resulting secret: shamir secret sharing

For more info, man ssss.

  • 1
    It would be a good idea to expert your key file and feed that file into ssss. – PyRulez Aug 10 '16 at 2:00
  • This is great! ssss is installed by default on Tails, so we have an easy way to boot into a secure environment when creating the secret. – Jonathan Cross Apr 20 '17 at 13:39
  • Looks like ssss wants only 128 bytes though... That's an annoying limitation. So you'd have to encrypt the seed, then use ssss on the encryption key. – user36303 Apr 20 '17 at 19:15

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