http://www.bouncycastle.org/java.html: The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 to JDK 1.8. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.operator.bc;

import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.encodings.PKCS1Encoding;
import org.bouncycastle.crypto.engines.RSAEngine;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;

public class BcRSAAsymmetricKeyUnwrapper
    extends BcAsymmetricKeyUnwrapper
{
    public BcRSAAsymmetricKeyUnwrapper(AlgorithmIdentifier encAlgId, AsymmetricKeyParameter privateKey)
    {
        super(encAlgId, privateKey);
    }

    protected AsymmetricBlockCipher createAsymmetricUnwrapper(ASN1ObjectIdentifier algorithm)
    {
        return new PKCS1Encoding(new RSAEngine());
    }
}