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.KEKRecipient;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.operator.OperatorException;
import org.bouncycastle.operator.SymmetricKeyUnwrapper;
import org.bouncycastle.operator.bc.BcSymmetricKeyUnwrapper;

public abstract class BcKEKRecipient
    implements KEKRecipient
{
    private SymmetricKeyUnwrapper unwrapper;

    public BcKEKRecipient(BcSymmetricKeyUnwrapper unwrapper)
    {
        this.unwrapper = unwrapper;
    }

    protected CipherParameters extractSecretKey(AlgorithmIdentifier keyEncryptionAlgorithm, AlgorithmIdentifier contentEncryptionAlgorithm, byte[] encryptedContentEncryptionKey)
        throws CMSException
    {
        try
        {
            return CMSUtils.getBcKey(unwrapper.generateUnwrappedKey(contentEncryptionAlgorithm, encryptedContentEncryptionKey));
        }
        catch (OperatorException e)
        {
            throw new CMSException("exception unwrapping key: " + e.getMessage(), e);
        }
    }
}