Shamir's Secret Sharing for cold storage of a Monero wallet

Question

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?

Answer 1

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.