This is a ruby library for Shamir’s Secret Sharing. ( 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