= shamir-secret-sharing

This is a ruby library for Shamir's Secret Sharing. ( http://en.wikipedia.org/wiki/Shamir's_Secret_Sharing )

== Compatible with...

• ruby 1.9.3
• ruby 2.0.0

== Installation

We assume you already have a ruby 1.9 or 2.0 compatible interpreter and rubygems environment.

git clone https://github.com/lian/shamir-secret-sharing.git; cd shamir-secret-sharing irb -Ilib -rshamir-secret-sharing

If you want to have it available system-wide, just build the gem and install it:

gem build shamir-secret-sharing.gemspec && gem install shamir-secret-sharing-*.gem

== Tests

The tests can be run with

rake

If you make changes to the code or add functionality, please also add tests.

= Example

== Split and Combine

split a secret into 4 shares. 3 of them are needed to combine the secret again.

shares = ShamirSecretSharing::Base58.split(secret="hello", available=4, needed=3) shares #=> ["FPGPdS98vRUCy9", "VmTjT28nES7Pck", "k9eRjVVpWP7uzj", "zXqDJNRpPttPjR"]

combine the secret again using at least 3 shares

ShamirSecretSharing::Base58.combine( ["VmTjT28nES7Pck", "zXqDJNRpPttPjR", "k9eRjVVpWP7uzj"] ) #=> "hello"

not enough shares

ShamirSecretSharing::Base58.combine( ["VmTjT28nES7Pck", "zXqDJNRpPttPjR"] ) #=> false

wrong shares

ShamirSecretSharing::Base58.combine( ["VmTjT28nES7Pck", "zXqDJNRpPttPjR", "some-wrong-share"] ) #=> false

== Encypt and Decrypt

Split and combine only work with a secret length below 512 bytes and the resulting share lengths are equivalent to the secret length. That means a 128 byte secret has a very long (128 byte) share length. Encrypt and decrypt are used to encrypt a large piece of data while keeping the share lengths to a fixed and reasonable size. It does that by AES-256-CBC encrypting the data with a random key and only then splitting that fixed size key into shares.

encrypt the data and create 4 shares. Later 3 shares and the encrypted data are needed to decrypt it again. This example uses a 96 bit random key for encryption.

shares, encrypted = ShamirSecretSharing::Base58.encrypt(data="Lorem ipsum dolor sit amet, consectetur adipiscing elit.", 4, 3, 96) shares #=> ["3QZNRFYZHKUpnv96cE6eVwPP", "5p611mjtxXBgPDx1m2SRwCKr", "8DcdGMD9i3kWGrYEVGtQLSWA", "Ad9NLPDVSnHfbqVhnmNn8YK4"] encrypted #=> "4PHcPwzzk48EjmusQz27t3X1rS7hAi9kwKgZJ7UMDR99rJgi19aHM8e7syh6uVrJ6HbcbgRmEUcR7hmkDvrYaJXH"

combine the shares and decrypt the encrypted data

ShamirSecretSharing::Base58.decrypt(["3QZNRFYZHKUpnv96cE6eVwPP", "8DcdGMD9i3kWGrYEVGtQLSWA", "Ad9NLPDVSnHfbqVhnmNn8YK4"], "4PHcPwzzk48EjmusQz27t3X1rS7hAi9kwKgZJ7UMDR99rJgi19aHM8e7syh6uVrJ6HbcbgRmEUcR7hmkDvrYaJXH") #=> "Lorem ipsum dolor sit amet, consectetur adipiscing elit."

not enough shares

ShamirSecretSharing::Base58.decrypt(["3QZNRFYZHKUpnv96cE6eVwPP", "8DcdGMD9i3kWGrYEVGtQLSWA"], "4PHcPwzzk48EjmusQz27t3X1rS7hAi9kwKgZJ7UMDR99rJgi19aHM8e7syh6uVrJ6HbcbgRmEUcR7hmkDvrYaJXH") #=> false

wrong shares

ShamirSecretSharing::Base58.decrypt(["3QZNRFYZHKUpnv96cE6eVwPP", "8DcdGMD9i3kWGrYEVGtQLSWA", "some-wrong-share"], "4PHcPwzzk48EjmusQz27t3X1rS7hAi9kwKgZJ7UMDR99rJgi19aHM8e7syh6uVrJ6HbcbgRmEUcR7hmkDvrYaJXH") #=> false

wrong encrypted data

ShamirSecretSharing::Base58.decrypt(["3QZNRFYZHKUpnv96cE6eVwPP", "8DcdGMD9i3kWGrYEVGtQLSWA", "Ad9NLPDVSnHfbqVhnmNn8YK4"], "wrong-encrypted-data") #=> false