This program is an implementation of Shamir's secret sharing. A secret can be split into multiple shares and a selectable number of shares is required to reconstruct the secret again.

Example

Passing a secret to secretshare for encoding:

$ echo My secret | ./secretshare -e2,5
2-1-LiTyeXwEP71IUA-Qj6n
2-2-i8OZZ1et6MgMvg-xwsJ
2-3-6J5LbU7KpRAw5A-27nn
2-4-3BBPWwHiWyKEfw-0ADd
2-5-v02dURiFFvq4JQ-zLIz

The parameters following the -e option tell secretshare to create 5 shares of which 2 will be necessary for decoding.

Decoding a subset of shares (one share per line) can be done like this:

$ echo -e "2-2-i8OZZ1et6MgMvg-xwsJ \n 2-4-3BBPWwHiWyKEfw-0ADd" | ./secretshare -d
My secret

Building

This project is Cargo-enabled. So, you should be able to build it with

$ cargo build --release

once you have made sure that rustc (the compiler) and cargo (the build and dependency management tool) are installed. Visit the Rust homepage if you don't know what they are.

I/O

The secret data does not have to be text. secretshare treats it as binary data. But, of course, you can feed it text as well. In the above example the echo command terminated the string with a line feed which is actually part of the secret and output as well after decoding. Note that, while secretshare supports secrets of up to 64 KiB it makes little sense to use such large secrets directly. In situations where you want to share larger secrets, you would usually pick a random password for encryption and use that password as secret for secretshare.

The generated shares are lines of ASCII text.

Structure of the shares

A share is built out of three or four parts: K-N-D-C (C is optional). K is one of the encoding parameters that tell you how many distinct shares of a specific secret are necessary to be able to recover the secret. The number N identifies the share (ranging from 1 to the number of shares that have been created). The D part is a Base64 encoding of a specific share's raw data. The optional part C is a Base64 encoding of a CRC-24 checksum of the share's data.