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.jcajce;

import java.security.Key;

import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.operator.GenericKey;

class OperatorUtils
{
    static Key getJceKey(GenericKey key)
    {
        if (key.getRepresentation() instanceof Key)
        {
            return (Key)key.getRepresentation();
        }

        if (key.getRepresentation() instanceof byte[])
        {
            return new SecretKeySpec((byte[])key.getRepresentation(), "ENC");
        }

        throw new IllegalArgumentException("unknown generic key type");
    }
}