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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. The APIs are designed primarily to be used in conjunction with the BC FIPS provider. The APIs may also be used with other providers although if being used in a FIPS context it is the responsibility of the user to ensure that any other providers used are FIPS certified.
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package org.bouncycastle.cms;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.bouncycastle.asn1.ASN1Encoding;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1Set;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.DERSet;
import org.bouncycastle.asn1.cms.AttributeTable;
import org.bouncycastle.asn1.cms.SignerIdentifier;
import org.bouncycastle.asn1.cms.SignerInfo;

import org.bouncycastle.asn1.nist.NISTObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.cert.X509CertificateHolder;
import org.bouncycastle.operator.ContentSigner;
import org.bouncycastle.operator.DefaultDigestAlgorithmIdentifierFinder;
import org.bouncycastle.operator.DigestAlgorithmIdentifierFinder;
import org.bouncycastle.operator.DigestCalculator;
import org.bouncycastle.operator.DigestCalculatorProvider;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.io.TeeOutputStream;

public class SignerInfoGenerator
{
    private final SignerIdentifier signerIdentifier;
    private final CMSAttributeTableGenerator sAttrGen;
    private final CMSAttributeTableGenerator unsAttrGen;
    private final ContentSigner signer;
    private final DigestCalculator digester;
    private final DigestAlgorithmIdentifierFinder digAlgFinder = new DefaultDigestAlgorithmIdentifierFinder();
    private final CMSSignatureEncryptionAlgorithmFinder sigEncAlgFinder;

    private byte[] calculatedDigest = null;
    private X509CertificateHolder certHolder;

    SignerInfoGenerator(
        SignerIdentifier signerIdentifier,
        ContentSigner signer,
        DigestCalculatorProvider digesterProvider,
        CMSSignatureEncryptionAlgorithmFinder sigEncAlgFinder)
        throws OperatorCreationException
    {
        this(signerIdentifier, signer, digesterProvider, sigEncAlgFinder, false);
    }

    SignerInfoGenerator(
        SignerIdentifier signerIdentifier,
        ContentSigner signer,
        DigestCalculatorProvider digesterProvider,
        CMSSignatureEncryptionAlgorithmFinder sigEncAlgFinder,
        boolean isDirectSignature)
        throws OperatorCreationException
    {
        this.signerIdentifier = signerIdentifier;
        this.signer = signer;

        if (digesterProvider != null)
        {
            this.digester = digesterProvider.get(digAlgFinder.find(signer.getAlgorithmIdentifier()));
        }
        else
        {
            this.digester = null;
        }

        if (isDirectSignature)
        {
            this.sAttrGen = null;
            this.unsAttrGen = null;
        }
        else
        {
            this.sAttrGen = new DefaultSignedAttributeTableGenerator();
            this.unsAttrGen = null;
        }

        this.sigEncAlgFinder = sigEncAlgFinder;
    }

    public SignerInfoGenerator(
        SignerInfoGenerator original,
        CMSAttributeTableGenerator sAttrGen,
        CMSAttributeTableGenerator unsAttrGen)
    {
        this.signerIdentifier = original.signerIdentifier;
        this.signer = original.signer;
        this.digester = original.digester;
        this.sigEncAlgFinder = original.sigEncAlgFinder;
        this.sAttrGen = sAttrGen;
        this.unsAttrGen = unsAttrGen;
    }

    SignerInfoGenerator(
        SignerIdentifier signerIdentifier,
        ContentSigner signer,
        DigestCalculatorProvider digesterProvider,
        CMSSignatureEncryptionAlgorithmFinder sigEncAlgFinder,
        CMSAttributeTableGenerator sAttrGen,
        CMSAttributeTableGenerator unsAttrGen)
        throws OperatorCreationException
    {
        this.signerIdentifier = signerIdentifier;
        this.signer = signer;

        if (digesterProvider != null)
        {
            this.digester = digesterProvider.get(digAlgFinder.find(signer.getAlgorithmIdentifier()));
        }
        else
        {
            this.digester = null;
        }

        this.sAttrGen = sAttrGen;
        this.unsAttrGen = unsAttrGen;
        this.sigEncAlgFinder = sigEncAlgFinder;
    }

    public SignerIdentifier getSID()
    {
        return signerIdentifier;
    }

    public int getGeneratedVersion()
    {
        return signerIdentifier.isTagged() ? 3 : 1;
    }

    public boolean hasAssociatedCertificate()
    {
        return certHolder != null;
    }

    public X509CertificateHolder getAssociatedCertificate()
    {
        return certHolder;
    }
    
    public AlgorithmIdentifier getDigestAlgorithm()
    {
        if (digester != null)
        {
            return digester.getAlgorithmIdentifier();
        }

        return digAlgFinder.find(signer.getAlgorithmIdentifier());
    }
    
    public OutputStream getCalculatingOutputStream()
    {
        if (digester != null)
        {
            if (sAttrGen == null)
            {
                return new TeeOutputStream(digester.getOutputStream(), signer.getOutputStream());    
            }
            return digester.getOutputStream();
        }
        else
        {
            return signer.getOutputStream();
        }
    }

    public SignerInfo generate(ASN1ObjectIdentifier contentType)
        throws CMSException
    {
        try
        {
            /* RFC 3852 5.4
             * The result of the message digest calculation process depends on
             * whether the signedAttrs field is present.  When the field is absent,
             * the result is just the message digest of the content as described
             *
             * above.  When the field is present, however, the result is the message
             * digest of the complete DER encoding of the SignedAttrs value
             * contained in the signedAttrs field.
             */
            ASN1Set signedAttr = null;

            AlgorithmIdentifier digestEncryptionAlgorithm = sigEncAlgFinder.findEncryptionAlgorithm(signer.getAlgorithmIdentifier());

            AlgorithmIdentifier digestAlg = null;

            if (sAttrGen != null)
            {
                digestAlg = digester.getAlgorithmIdentifier();
                calculatedDigest = digester.getDigest();
                Map parameters = getBaseParameters(contentType, digester.getAlgorithmIdentifier(), digestEncryptionAlgorithm, calculatedDigest);
                AttributeTable signed = sAttrGen.getAttributes(Collections.unmodifiableMap(parameters));

                signedAttr = getAttributeSet(signed);

                // sig must be composed from the DER encoding.
                OutputStream sOut = signer.getOutputStream();

                sOut.write(signedAttr.getEncoded(ASN1Encoding.DER));

                sOut.close();
            }
            else
            {
                if (digester != null)
                {
                    digestAlg = digester.getAlgorithmIdentifier();
                    calculatedDigest = digester.getDigest();
                }
                else
                {
                    digestAlg = digAlgFinder.find(signer.getAlgorithmIdentifier());
                    calculatedDigest = null;
                }
            }

            byte[] sigBytes = signer.getSignature();

            ASN1Set unsignedAttr = null;
            if (unsAttrGen != null)
            {
                Map parameters = getBaseParameters(contentType, digestAlg, digestEncryptionAlgorithm, calculatedDigest);
                parameters.put(CMSAttributeTableGenerator.SIGNATURE, Arrays.clone(sigBytes));

                AttributeTable unsigned = unsAttrGen.getAttributes(Collections.unmodifiableMap(parameters));

                unsignedAttr = getAttributeSet(unsigned);
            }

            if (sAttrGen == null)
            {
                // RFC 8419, Section 3.2 - needs to be shake-256, not shake-256-len
                if (EdECObjectIdentifiers.id_Ed448.equals(digestEncryptionAlgorithm.getAlgorithm()))
                {
                    digestAlg = new AlgorithmIdentifier(NISTObjectIdentifiers.id_shake256);
                }
            }
            
            return new SignerInfo(signerIdentifier, digestAlg,
                signedAttr, digestEncryptionAlgorithm, new DEROctetString(sigBytes), unsignedAttr);
        }
        catch (IOException e)
        {
            throw new CMSException("encoding error.", e);
        }
    }

    void setAssociatedCertificate(X509CertificateHolder certHolder)
    {
        this.certHolder = certHolder;
    }

    private ASN1Set getAttributeSet(
        AttributeTable attr)
    {
        if (attr != null)
        {
            return new DERSet(attr.toASN1EncodableVector());
        }

        return null;
    }

    private Map getBaseParameters(ASN1ObjectIdentifier contentType, AlgorithmIdentifier digAlgId, AlgorithmIdentifier sigAlgId, byte[] hash)
    {
        Map param = new HashMap();

        if (contentType != null)
        {
            param.put(CMSAttributeTableGenerator.CONTENT_TYPE, contentType);
        }

        param.put(CMSAttributeTableGenerator.DIGEST_ALGORITHM_IDENTIFIER, digAlgId);
        param.put(CMSAttributeTableGenerator.SIGNATURE_ALGORITHM_IDENTIFIER, sigAlgId);
        param.put(CMSAttributeTableGenerator.DIGEST,  Arrays.clone(hash));

        return param;
    }

    public byte[] getCalculatedDigest()
    {
        if (calculatedDigest != null)
        {
            return Arrays.clone(calculatedDigest);
        }

        return null;
    }

    public CMSAttributeTableGenerator getSignedAttributeTableGenerator()
    {
        return sAttrGen;
    }

    public CMSAttributeTableGenerator getUnsignedAttributeTableGenerator()
    {
        return unsAttrGen;
    }
}