http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.pqc.jcajce.interfaces;

import java.security.PrivateKey;


Base interface for an XMSS private key

/**
 * Base interface for an XMSS private key
 */
public interface XMSSPrivateKey
    extends XMSSKey, PrivateKey
{
    
Return the number of usages left for the private key.

Returns:the number of times the key can be used before it is exhausted.
/**
     * Return the number of usages left for the private key.
     *
     * @return the number of times the key can be used before it is exhausted.
     */
    long getUsagesRemaining();
}