Horcrux - Rust implementation of Shamir's Secret Sharing

This program is an example implementation of Shamir's Secret Sharing in Rust.

You can find more details in this blog post.

Disclaimer

This program is a prototype that shouldn't be used in production. In particular, the code does not provide any constant-time guarantees (or rather, I can guarantee that it's not constant time), and no security audit was conducted.

Usage

I recommend using the following Rust compiler flags to enable optimizations: RUSTFLAGS='-C target-cpu=native'. The best optimizations will be available on x86_64 CPUs that support CLMUL instructions (any recent Intel CPU), but Horcrux should work on any Rust-supported platform.

The example CLI program will generate a random secret before splitting it into shares.

$ RUSTFLAGS='-C target-cpu=native' cargo +nightly run -- --nshares 10 --threshold 3 split
Secret = 3f5ffcd50ac6d0ece12bd0063e0c5f6e1c3e317f2d4692a3237fac857b85bca5
Polynom = 3f5ffcd50ac6d0ece12bd0063e0c5f6e1c3e317f2d4692a3237fac857b85bca5
    + 53ef0c80c3408ef4eba9f9bd8f3bab4b400432510a39f838a74123c5710ae894 x^1
    + 010a53a157042e1a1db679ee8501b63612eff8e497f6e47e00eb96886114f6cc x^2
Shares:
1|6dbaa3f49e82700217345055343642134ed5fbcab0898ee584d519c86b9ba2fd
2|9ca8ab51d057714940a1c4c7347dd120d789b64f66eef32a6e53b12e1dc3b6bd
3|ce4df4704413d1a7b6be44943e47cc5d85627cfafb21ef6cc9f904630ddda8e5
4|6046f4c3778602d694eba81852f9912332d176727acf35a1b0c24b16aee17235
5|32a3abe2e3c2a23862f4284b58c38c5e603abcc7e70029e71768fe5bbeff6c6d
6|c3b1a347ad17a3733561bcd958881f6df966f14231675428fdee56bdc8a7782d
7|9154fc663953039dc37e3c8a52b20210ab8d3bf7aca8486e5a44e3f0d8b96675
8|e2b37086d1c9357dd1fa664b07bc88b4a7e19ad281304ce3239310b6b6ef4b03
9|b0562fa7458d959327e5e6180d8695c9f50a50671cff50a58439a5fba6f1555b
10|414427020b5894d87070728a0dcd06fa6c561de2ca982d6a6ebf0d1dd0a9411b

With enough shares (here at least the threshold of 3) stored in a file...

$ cat shares.txt 
3|ce4df4704413d1a7b6be44943e47cc5d85627cfafb21ef6cc9f904630ddda8e5
5|32a3abe2e3c2a23862f4284b58c38c5e603abcc7e70029e71768fe5bbeff6c6d
8|e2b37086d1c9357dd1fa664b07bc88b4a7e19ad281304ce3239310b6b6ef4b03

...you can then reconstruct the secret.

$ RUSTFLAGS='-C target-cpu=native' cargo +nightly run -- --nshares 10 --threshold 3 reconstruct --shares shares.txt 
Shares:
3|ce4df4704413d1a7b6be44943e47cc5d85627cfafb21ef6cc9f904630ddda8e5
5|32a3abe2e3c2a23862f4284b58c38c5e603abcc7e70029e71768fe5bbeff6c6d
8|e2b37086d1c9357dd1fa664b07bc88b4a7e19ad281304ce3239310b6b6ef4b03
Secret = 3f5ffcd50ac6d0ece12bd0063e0c5f6e1c3e317f2d4692a3237fac857b85bca5

You can also use the randomized share format.

$ RUSTFLAGS='-C target-cpu=native' cargo +nightly run -- --nshares 10 --threshold 3 --type random split
Secret = 2408cba555804bdcc8cd6cd3e76635568d6954029fdd092e3e99b16f6f6241f2
Polynom = 2408cba555804bdcc8cd6cd3e76635568d6954029fdd092e3e99b16f6f6241f2
    + a4df09420c887b9725b01df1e28a0fe6d10c547d006045f143823c0cc404ab28 x^1
    + 55d84ab1d33f2ff36f5e2547dfb8aa4170eb9bff1e66876c83ba963bb481b2e7 x^2
Shares:
75b8f1bba44c54aa6841eb58c2626fcf5096a675599a5934f41fc3cc528fd1ac|6e0d18901b948d37ed701bdd6805d9c45cbad1afb77380678e657723e7126eef
418ed35d5ec86561923a11aa33649c236e7bd0aa7dec82bb15e3dcb1b2ea3a17|b928705aa179c1050533695da69b06c77496466ea12fecef23f254cd68796bac
7f716b6de2ac4ef6c7ea201488e9c254d74d64cdf04fe91d5dde1342ec6f1813|6aa2b4bd28dfcf1b1c69301c7779200513d9b1de79f07c882a1bb6d155612254
1633d38b76c4cac331db3b245c2ff34daa30a5198ff5cfbd6ed8f1529b083dc5|e4266b22bafddfb49b3be1c78f3b2e1f63968a5ecd0084d2e36693587738b137
960cdcaba460189e6b84d154dcc7ae4877c7dfeaa2b738dddaa74d6ef8f47e04|5ac61ba75e69c30f77805bd06c3c8d70f5550a67f1bc695fb62f4a57efdb65a8
1286517fac0ae2abfe08fb5d5a9ad106adf7b7899de412001831f3a05f34fe97|cf8722b550ba55596b54e1e63579d5f6e20eae4495d949eb9dc080ce8886a756
b0c1cbe91f9e32374288a859d8b21e655c11a9022d72544b32a1ba9524fee799|3a95a6404deda8994c49c0d363e36adf87974bb605b43100e2d504dae7f9c4ef
b928b70fa8f7d956d8e1c71062451b27ed46f39eb07fbfa7bb4fcf2af932b29f|0ab5e1d9f58cf36d9e0babdf953299589584a3437d4538b974678925ebf59372
2498f9c896eee14dddb5079c3aeee0f83543c4e835a2620a4673d784578333db|c11cf808ac0c72d845a6b3e1c8f02c9332f7735f3d82cc54f40826f038c749ac
55afe90588baa5e91fb002d926ea0ee43278b7d7c7a9db7d431f6b0ac2d8dc2c|89c5b32a1d546995b891b503a39d36e79ab74ede8dd159ac392f4aa0d9d9e3fb

Tests and benchmarks

Many unit tests and micro-benchmarks are included, don't forget to compile for the native CPU architecture for the best optimizations.

There are hundreds of them, so it may take a while to run them all.

$ RUSTFLAGS='-C target-cpu=native' cargo +nightly test --all
$ RUSTFLAGS='-C target-cpu=native' cargo +nightly bench --all