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.crypto.CipherParameters;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.operator.GenericKey;

class CMSUtils
{
    static CipherParameters getBcKey(GenericKey key)
    {
        if (key.getRepresentation() instanceof CipherParameters)
        {
            return (CipherParameters)key.getRepresentation();
        }

        if (key.getRepresentation() instanceof byte[])
        {
            return new KeyParameter((byte[])key.getRepresentation());
        }

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