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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.8 and up. The APIs are designed primarily to be used in conjunction with the BC LTS provider but may also be used with other providers providing cryptographic services.

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package org.bouncycastle.operator.jcajce;

import java.io.IOException;
import java.io.OutputStream;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.Provider;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.jcajce.util.DefaultJcaJceHelper;
import org.bouncycastle.jcajce.util.JcaJceHelper;
import org.bouncycastle.jcajce.util.NamedJcaJceHelper;
import org.bouncycastle.jcajce.util.ProviderJcaJceHelper;
import org.bouncycastle.operator.DigestCalculator;
import org.bouncycastle.operator.DigestCalculatorProvider;
import org.bouncycastle.operator.OperatorCreationException;

public class JcaDigestCalculatorProviderBuilder
{
    private OperatorHelper helper = new OperatorHelper(new DefaultJcaJceHelper());

    public JcaDigestCalculatorProviderBuilder()
    {
    }


    public JcaDigestCalculatorProviderBuilder setHelper(JcaJceHelper helper)
    {
        this.helper = new OperatorHelper(helper);

        return this;
    }

    public JcaDigestCalculatorProviderBuilder setProvider(Provider provider)
    {
        this.helper = new OperatorHelper(new ProviderJcaJceHelper(provider));

        return this;
    }

    public JcaDigestCalculatorProviderBuilder setProvider(String providerName)
    {
        this.helper = new OperatorHelper(new NamedJcaJceHelper(providerName));

        return this;
    }

    public DigestCalculatorProvider build()
        throws OperatorCreationException
    {
        return new DigestCalculatorProvider()
        {
            public DigestCalculator get(final AlgorithmIdentifier algorithm)
                throws OperatorCreationException
            {
                final DigestOutputStream stream;

                try
                {
                    MessageDigest dig = helper.createDigest(algorithm);

                    stream = new DigestOutputStream(dig);
                }
                catch (GeneralSecurityException e)
                {
                    throw new OperatorCreationException("exception on setup: " + e, e);
                }

                return new DigestCalculator()
                {
                    public AlgorithmIdentifier getAlgorithmIdentifier()
                    {
                        return algorithm;
                    }

                    public OutputStream getOutputStream()
                    {
                        return stream;
                    }

                    public byte[] getDigest()
                    {
                        return stream.getDigest();
                    }
                };
            }
        };
    }

    private static class DigestOutputStream
        extends OutputStream
    {
        private MessageDigest dig;

        DigestOutputStream(MessageDigest dig)
        {
            this.dig = dig;
        }

        public void write(byte[] bytes, int off, int len)
            throws IOException
        {
            dig.update(bytes, off, len);
        }

        public void write(byte[] bytes)
            throws IOException
        {
            dig.update(bytes);
        }

        public void write(int b)
            throws IOException
        {
            dig.update((byte)b);
        }

        byte[] getDigest()
        {
            return dig.digest();
        }
    }
}