com.codahale.shamir

Class Scheme

java.lang.Object

com.codahale.shamir.Scheme

public abstract class Scheme
extends Object

Scheme implemented Shamir's Secret Sharing over GF(256) to securely split secrets into N parts, of which any K can be joined to recover the original secret.

Scheme uses the same GF(256) field polynomial as the Advanced Encryption Standard (AES): 0x11b, or x⁸ + x⁴ + x³ + x + 1.

See Also:

Shamir's Secret Sharing, The Finite Field {@code GF(256)}

Constructor Summary

Constructors

Constructor and Description
Scheme()

Method Summary

Modifier and Type	Method and Description
byte[]	join(Map<Integer,byte[]> parts) Joins the given parts to recover the original secret.
abstract int	k() The number of parts the scheme will require to re-create a secret.
abstract int	n() The number of parts the scheme will generate when splitting a secret.
static Scheme	of(int n, int k) Creates a new Scheme instance.
Map<Integer,byte[]>	split(byte[] secret) Splits the given secret into n parts, of which any k or more can be combined to recover the original secret.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Scheme

public Scheme()

Method Detail

of

@CheckReturnValue
public static Scheme of(@Nonnegative
                                          int n,
                                          @Nonnegative
                                          int k)

Creates a new Scheme instance.

Parameters:

n - the number of parts to produce (must be >1)

k - the threshold of joinable parts (must be <= n)

Returns:

an N/K Scheme

n

public abstract int n()

The number of parts the scheme will generate when splitting a secret.

Returns:

N

k

public abstract int k()

The number of parts the scheme will require to re-create a secret.

Returns:

K

split

@CheckReturnValue
public Map<Integer,byte[]> split(byte[] secret)

Splits the given secret into n parts, of which any k or more can be combined to recover the original secret.

Parameters:

secret - the secret to split

Returns:

a map of n part IDs and their values

join

@CheckReturnValue
public byte[] join(Map<Integer,byte[]> parts)

Joins the given parts to recover the original secret.

N.B.: There is no way to determine whether or not the returned value is actually the original secret. If the parts are incorrect, or are under the threshold value used to split the secret, a random value will be returned.

Parameters:

parts - a map of part IDs to part values

Returns:

the original secret

Throws:

IllegalArgumentException - if parts is empty or contains values of varying lengths