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;

import java.io.InputStream;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.operator.InputDecryptor;
import org.bouncycastle.operator.MacCalculator;
import org.bouncycastle.util.io.TeeInputStream;

public class RecipientOperator
{
    private final AlgorithmIdentifier algorithmIdentifier;
    private final Object operator;

    public RecipientOperator(InputDecryptor decryptor)
    {
        this.algorithmIdentifier = decryptor.getAlgorithmIdentifier();
        this.operator = decryptor;
    }

    public RecipientOperator(MacCalculator macCalculator)
    {
        this.algorithmIdentifier = macCalculator.getAlgorithmIdentifier();
        this.operator = macCalculator;
    }

    public InputStream getInputStream(InputStream dataIn)
    {
        if (operator instanceof InputDecryptor)
        {
            return ((InputDecryptor)operator).getInputStream(dataIn);
        }
        else
        {
            return new TeeInputStream(dataIn, ((MacCalculator)operator).getOutputStream());
        }
    }

    public boolean isMacBased()
    {
        return operator instanceof MacCalculator;
    }

    public byte[] getMac()
    {
        return ((MacCalculator)operator).getMac();
    }
}