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.bc;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.Signer;
import org.bouncycastle.crypto.signers.RSADigestSigner;
import org.bouncycastle.operator.OperatorCreationException;

public class BcRSAContentSignerBuilder
    extends BcContentSignerBuilder
{
    public BcRSAContentSignerBuilder(AlgorithmIdentifier sigAlgId, AlgorithmIdentifier digAlgId)
    {
        super(sigAlgId, digAlgId);
    }

    protected Signer createSigner(AlgorithmIdentifier sigAlgId, AlgorithmIdentifier digAlgId)
        throws OperatorCreationException
    {
        Digest dig = digestProvider.get(digAlgId);

        return new RSADigestSigner(dig);
    }
}