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.cms.bc;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.KeyTransRecipient;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.operator.AsymmetricKeyUnwrapper;
import org.bouncycastle.operator.OperatorException;
import org.bouncycastle.operator.bc.BcRSAAsymmetricKeyUnwrapper;

public abstract class BcKeyTransRecipient
    implements KeyTransRecipient
{
    private AsymmetricKeyParameter recipientKey;

    public BcKeyTransRecipient(AsymmetricKeyParameter recipientKey)
    {
        this.recipientKey = recipientKey;
    }

    protected CipherParameters extractSecretKey(AlgorithmIdentifier keyEncryptionAlgorithm, AlgorithmIdentifier encryptedKeyAlgorithm, byte[] encryptedEncryptionKey)
        throws CMSException
    {
        AsymmetricKeyUnwrapper unwrapper = new BcRSAAsymmetricKeyUnwrapper(keyEncryptionAlgorithm, recipientKey);

        try
        {
            return CMSUtils.getBcKey(unwrapper.generateUnwrappedKey(encryptedKeyAlgorithm, encryptedEncryptionKey));
        }
        catch (OperatorException e)
        {
            throw new CMSException("exception unwrapping key: " + e.getMessage(), e);
        }
    }
}