NEVER USE THIS

NEVER USE THIS. I am not a cryptography specialist. You should only use cryptographic functions that were implemented by a specialist in cryptography and have been carefully vetted and tested. Otherwise, they are liable to have vulnerabilities. This library is subject to timing attacks. This software is purely for instructional purposes.

Description

secret-sharing provides the ability to split a secret into shares, which may later be combined to reconstruct the secret. When splitting a secret, a sharesNeeded number is passed in as an argument. The secret can later be reconstructed by calling SecretSharing.reconstructSecret with an array of sharesNeeded distincts shares. For example, secret-sharing could be used to split a secret into five shares, any three of which could be used to reconstruct the secret.

secret-sharing uses Shamir's Secret Sharing algorithm. This is an information-theoretically secure algorithm. This means that possession of sharesNeeded - 1 secret shares gives no information at all about the secret, apart from the number of bytes it contains. (That is, given a specific value for the secret, a set of sharesNeeded - 1 secret shares will have the same random distribution as they would for any other specific secret of the same length. This assumes that the random number generator is perfectly random. In practice, it is not perfectly random, so the above claims must be relaxed accordingly.)

Features

• Split a secret into multiple shares, which may later be combined to recover the secret.
• Uses an information-theoretically secure algorithm.
• Additional shares can be generated as needed. It is not necessary to generate all of the shares up front.

Limitations

• Not written by a cryptography specialist or carefully vetted or tested. For these reasons, this library is liable to have vulnerabilities and should never be used.
• Timing attacks are possible. In other words, information-theoretic security is not guaranteed if an attacker has knowledge of how long the method calls took to run.

Example

// Generate secret shares, with 3 of 5 needed to reconstruct the secret
byte[] secret = "a 128-bit secret".getBytes(StandardCharsets.US_ASCII);
byte[][] shares = SecretSharing.splitSecret(secret, 3, 5);

// Print the shares
for (byte[] share : shares) {
    System.out.println(Base64.getEncoder().encodeToString(share));
}

// Reconstruct the secret
byte[] reconstructedSecret = SecretSharing.reconstructSecret(
    new byte[][]{shares[0], shares[1], shares[4]});
Arrays.equals(secret, reconstructedSecret); // Returns true

Documentation

See https://btrekkie.github.io/secret-sharing/index.html for API documentation.