Module java.base

Package javax.crypto

Class KEM.Decapsulator

java.lang.Object

javax.crypto.KEM.Decapsulator

Enclosing class:

KEM

public static final class KEM.Decapsulator
extends Object

A decapsulator, generated by KEM.newDecapsulator(java.security.PrivateKey) on the KEM receiver side.

This class represents the key decapsulation function of a KEM. An invocation of the decapsulate method recovers the secret key from the key encapsulation message.

API Note:

This class is defined in Java SE 17 Maintenance Release 1.

Since:

17

Method Summary

Modifier and Type	Method	Description
SecretKey	decapsulate(byte[] encapsulation)	The key decapsulation function.
SecretKey	decapsulate(byte[] encapsulation, int from, int to, String algorithm)	The key decapsulation function.
int	encapsulationSize()	Returns the size of the key encapsulation message.
String	providerName()	Returns the name of the provider.
int	secretSize()	Returns the size of the shared secret.

Methods declared in class java.lang.Object

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

Method Details

providerName

public String providerName()

Returns the name of the provider.

Returns:

the name of the provider

decapsulate

public SecretKey decapsulate(byte[] encapsulation)
                      throws DecapsulateException

The key decapsulation function.

This method is equivalent to decapsulate(encapsulation, 0, secretSize(), "Generic"). This combination of arguments must be supported by every implementation.

The generated secret key is usually passed to a key derivation function (KDF) as the input keying material.

Parameters:

encapsulation - the key encapsulation message from the sender. The size must be equal to the value returned by encapsulationSize(), or a DecapsulateException will be thrown.

Returns:

the shared secret as a SecretKey with an algorithm name of "Generic"

Throws:

DecapsulateException - if an error occurs during the decapsulation process

NullPointerException - if encapsulation is null

decapsulate

public SecretKey decapsulate(byte[] encapsulation,
 int from,
 int to,
 String algorithm)
                      throws DecapsulateException

The key decapsulation function.

An invocation of this method recovers the secret key from the key encapsulation message.

An implementation may choose to not support arbitrary combinations of from, to, and algorithm.

Parameters:

encapsulation - the key encapsulation message from the sender. The size must be equal to the value returned by encapsulationSize(), or a DecapsulateException will be thrown.

from - the initial index of the shared secret byte array to be returned, inclusive

to - the final index of the shared secret byte array to be returned, exclusive

algorithm - the algorithm name for the secret key that is returned

Returns:

a portion of the shared secret as a SecretKey containing the bytes of the secret ranging from from to to, exclusive, and an algorithm name as specified. For example, decapsulate(encapsulation, secretSize() - 16, secretSize(), "AES") uses the last 16 bytes of the shared secret as a 128-bit AES key.

Throws:

DecapsulateException - if an error occurs during the decapsulation process

IndexOutOfBoundsException - if from < 0, from > to, or to > secretSize()

NullPointerException - if encapsulation or algorithm is null

UnsupportedOperationException - if the combination of from, to, and algorithm is not supported by the decapsulator

secretSize

public int secretSize()

Returns the size of the shared secret.

This method can be called to find out the length of the shared secret before decapsulate is called or if the obtained SecretKey is not extractable.

Returns:

the size of the shared secret

encapsulationSize

public int encapsulationSize()

Returns the size of the key encapsulation message.

This method can be used to extract the encapsulation message from a longer byte array if no length information is provided by a higher level protocol.

Returns:

the size of the key encapsulation message