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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.its.bc;

import java.io.IOException;
import java.io.OutputStream;

import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.nist.NISTObjectIdentifiers;
import org.bouncycastle.asn1.sec.SECObjectIdentifiers;
import org.bouncycastle.asn1.teletrust.TeleTrusTObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.io.DigestOutputStream;
import org.bouncycastle.crypto.params.ECNamedDomainParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.signers.DSADigestSigner;
import org.bouncycastle.crypto.signers.ECDSASigner;
import org.bouncycastle.its.ITSCertificate;
import org.bouncycastle.its.operator.ITSContentSigner;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.operator.bc.BcDefaultDigestProvider;
import org.bouncycastle.util.Arrays;

public class BcITSContentSigner
    implements ITSContentSigner
{
    private final ECPrivateKeyParameters privKey;
    private final ITSCertificate signerCert;
    private final AlgorithmIdentifier digestAlgo;
    private final Digest digest;
    private final byte[] parentData;
    private final ASN1ObjectIdentifier curveID;
    private final byte[] parentDigest;

    /**
     * Constructor for self-signing.
     *
     * @param privKey
     */
    public BcITSContentSigner(ECPrivateKeyParameters privKey)
    {
        this(privKey, null);
    }

    public BcITSContentSigner(ECPrivateKeyParameters privKey, ITSCertificate signerCert)
    {
        this.privKey = privKey;
        this.curveID = ((ECNamedDomainParameters)privKey.getParameters()).getName();
        this.signerCert = signerCert;
        if (curveID.equals(SECObjectIdentifiers.secp256r1))
        {
            digestAlgo = new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha256);
        }
        else if (curveID.equals(TeleTrusTObjectIdentifiers.brainpoolP256r1))
        {
            digestAlgo = new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha256);
        }
        else if (curveID.equals(TeleTrusTObjectIdentifiers.brainpoolP384r1))
        {
            digestAlgo = new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha384);
        }
        else
        {
            throw new IllegalArgumentException("unknown key type");
        }

        try
        {
            this.digest = BcDefaultDigestProvider.INSTANCE.get(digestAlgo);
        }
        catch (OperatorCreationException e)
        {
            throw new IllegalStateException("cannot recognise digest type: " + digestAlgo.getAlgorithm());
        }

        if (signerCert != null)
        {
            try
            {
                this.parentData = signerCert.getEncoded();
                this.parentDigest = new byte[digest.getDigestSize()];

                digest.update(parentData, 0, parentData.length);

                digest.doFinal(parentDigest, 0);
            }
            catch (IOException e)
            {
                throw new IllegalStateException("signer certificate encoding failed: " + e.getMessage());
            }
        }
        else
        {
            // self signed so we use a null digest for the parent.
            this.parentData = null;
            this.parentDigest = new byte[digest.getDigestSize()];
            digest.doFinal(parentDigest, 0);
        }
    }

    public ITSCertificate getAssociatedCertificate()
    {
        return signerCert;
    }

    public byte[] getAssociatedCertificateDigest()
    {
        return Arrays.clone(parentDigest);
    }

    public AlgorithmIdentifier getDigestAlgorithm()
    {
        return digestAlgo;
    }

    public OutputStream getOutputStream()
    {
        return new DigestOutputStream(digest);
    }

    public boolean isForSelfSigning()
    {
        return parentData == null;
    }

    public ASN1ObjectIdentifier getCurveID()
    {
        return curveID;
    }

    public byte[] getSignature()
    {
        byte[] clientCertDigest = new byte[digest.getDigestSize()];

        digest.doFinal(clientCertDigest, 0);

        final DSADigestSigner signer = new DSADigestSigner(new ECDSASigner(), digest);

        signer.init(true, privKey);

        signer.update(clientCertDigest, 0, clientCertDigest.length);

        signer.update(parentDigest, 0, parentDigest.length);

        return signer.generateSignature();
    }
}