This simple program will help you run Shamir’s Secret Sharing algorithm on any file using the
merge commands. It also contains tools to easily
generate an AES key and
decrypt files using said key.
There is a bitcoin bounty ready to be claimed if you can bypass this scheme.
If you are backing up a bitcoin wallet, you might be better off doing something with multisig. This article summarizes some of the drawbacks of Shamir, but I think in some cases it’s still a good solution!
This is not security-hardened code. Use at your own risk.
Encrypt and Decrypt Files
# Generate a new AES Key shush generate my.key # Encrypt a secret file or archive with your AES Key shush encrypt -key=my.key secrets.tar # Decrypt a payload using an AES key shush decrypt -key=my.key secrets.tar.shush
Split and Merge with Shamir’s Secret Sharing Algorithm
# Split a file into 5 shards, requiring a threshold of at least 3 shards for recovery shush split -t=3 -s=5 my.key # Merge shards back into the original file shush merge my.key.shard0 my.key.shard2 my.key.shard4 # On unix you can also use a wildcard, if the names are preserved. shush merge my.key.shard*
Build & Install
# On a unix-based system with go installed... go build -o shush main.go # install on your system mv shush /usr/local/bin
Why is this useful?
If you’ve distributed the shards of an AES key to your team (read: family, friends, coworkers), they will be able to recover any encrypted data in case you lose it, become incapacitated, or worse.
Can’t I just split a key into chunks, and distribute the chunks?
With Shamir’s algorithm, you can specify a
threshold for recovery that is lower than the total number of
shards. This approach protects you against some members of your team losing their shards.
How do I safely generate and distribute shards & encrypted payloads?
Run this program in Tails with no internet connection. Be extremely careful about how you store your key! Distribute shards to your team on physical media (like flash drives). You may also want to notify your team members who else is on their team, but ideally that information will live in their heads, not in their emails.
What should I include when distributing shards?
You may want to consider including any of the following things when distributing shards:
- instructions on how to merge shards and decrypt files
- information about the location of other potential payloads
- a copy of the encrypted payload(s)
- a copy of shush
- a copy of the shush source code
How do I safely merge shards and decrypt payloads?
Since the payload likely has sensitive contents, you should take similar precautions (tails, offline, etc.) when re-assembling keys and decrypting payloads.
Can I encrypt additional or updated secrets?
If you hold onto your original AES key, you can create new encrypted payloads whenever you want, and redistribute or upload just the payload without having to generate new keys or distribute new shards.
What stops the people on my team from coordinating to steal my secrets against my will?
Nothing. Choose your team wisely.