Shamir's Secret Sharing

This project is based on Coda Hale's implementation of Shamir's Secret Sharing

I have wrapped and simplified the API so it better fits my needs. I also found out that I could have static methods for creating shares and recreate secret.

class Shamir

public class Shamir {

    // s: secret
    // n: share count
    // k: minimum keys to recreate secret
    public static List<String> getShares(String s, int n, int k) {
        // code omitted
    }

    // provide k unique shares to recreate secret
    public static String getSecret(String... shares) {
        // code omitted
    }
}

Hale's Scheme use Map<Integer, byte[]>. I wanted something simpler and am now using List<String> instead by doing the following:

• Base64 encode the map var firstEncoding = encode(value)
• Concatenate the maps key and encoded value like this key + firstEncoding. Ex. 1+tRMnJCzlIxaDFSRmM=
• Base64 encode a second time
• return the list with all shares

To get the secret I just do the opposite

How to use (example)

Step 1 - Create Shares

• -> secret to encrypt and split
• -> n specifies unique shares.
• -> k specifies unique shares needed to recreate secret
• <- List with n unique shares

Step 2 - Recreate Secret

• -> k unique shares
• <- secret

 class ShamirTest {

    @Test
    void test() {
        String secret = "My secret";
        
        int n = 5;
        int k = 3;
        
        // Create shares
        List<String> shares = Shamir.getShares(secret, n, k); 
        System.out.println(shares); // list shares for distribution

        // Bring back secret
        String actual = Shamir.getSecret(shares.get(0), shares.get(1), shares.get(2)); // provide at least k unique shares
        System.out.println(actual);

        assertEquals(secret, actual);
    }
}

Example output

[MStqZDB4NUpwRHdzenM=, MitnKzdRK3VKQlpiakU=, MytRMHJCYlIxaDFSRmM=, NCtoWEcrdk9PMDk2SlY=, NStSZFd2S3h5VVJ3dk4=]
My secret

Dependency needed

<dependency>
  <groupId>com.codahale</groupId>
  <artifactId>shamir</artifactId>
  <version>0.7.0</version>
</dependency>