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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 org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERNull;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.cms.KeyAgreeRecipientInfo;
import org.bouncycastle.asn1.cms.OriginatorIdentifierOrKey;
import org.bouncycastle.asn1.cms.OriginatorPublicKey;
import org.bouncycastle.asn1.cms.RecipientInfo;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.operator.GenericKey;

public abstract class KeyAgreeRecipientInfoGenerator
    implements RecipientInfoGenerator
{
    private ASN1ObjectIdentifier keyAgreementOID;
    private ASN1ObjectIdentifier keyEncryptionOID;
    private SubjectPublicKeyInfo originatorKeyInfo;

    protected KeyAgreeRecipientInfoGenerator(ASN1ObjectIdentifier keyAgreementOID, SubjectPublicKeyInfo originatorKeyInfo, ASN1ObjectIdentifier keyEncryptionOID)
    {
        this.originatorKeyInfo = originatorKeyInfo;
        this.keyAgreementOID = keyAgreementOID;
        this.keyEncryptionOID = keyEncryptionOID;
    }

    public RecipientInfo generate(GenericKey contentEncryptionKey)
        throws CMSException
    {
        OriginatorIdentifierOrKey originator = new OriginatorIdentifierOrKey(
            createOriginatorPublicKey(originatorKeyInfo));

        AlgorithmIdentifier keyEncAlg;
        if (CMSUtils.isDES(keyEncryptionOID.getId()) || keyEncryptionOID.equals(PKCSObjectIdentifiers.id_alg_CMSRC2wrap))
        {
            keyEncAlg = new AlgorithmIdentifier(keyEncryptionOID, DERNull.INSTANCE);
        }
//        else if (CMSUtils.isGOST(keyAgreementOID))
//        {
//            keyEncAlg = new AlgorithmIdentifier(keyEncryptionOID, new Gost2814789KeyWrapParameters(CryptoProObjectIdentifiers.id_Gost28147_89_CryptoPro_A_ParamSet));
//        }
        else
        {
            keyEncAlg = new AlgorithmIdentifier(keyEncryptionOID);
        }

        AlgorithmIdentifier keyAgreeAlg = new AlgorithmIdentifier(keyAgreementOID, keyEncAlg);

        ASN1Sequence recipients = generateRecipientEncryptedKeys(keyAgreeAlg, keyEncAlg, contentEncryptionKey);
        byte[] userKeyingMaterial = getUserKeyingMaterial(keyAgreeAlg);

        if (userKeyingMaterial != null)
        {
            return new RecipientInfo(new KeyAgreeRecipientInfo(originator, new DEROctetString(userKeyingMaterial),
                keyAgreeAlg, recipients));
        }
        else
        {
            return new RecipientInfo(new KeyAgreeRecipientInfo(originator, null, keyAgreeAlg, recipients));
        }
    }

    protected OriginatorPublicKey createOriginatorPublicKey(SubjectPublicKeyInfo originatorKeyInfo)
    {
        return new OriginatorPublicKey(
            new AlgorithmIdentifier(originatorKeyInfo.getAlgorithm().getAlgorithm(), DERNull.INSTANCE),
            originatorKeyInfo.getPublicKeyData().getBytes());
    }

    protected abstract ASN1Sequence generateRecipientEncryptedKeys(AlgorithmIdentifier keyAgreeAlgorithm, AlgorithmIdentifier keyEncAlgorithm, GenericKey contentEncryptionKey)
        throws CMSException;

    protected abstract byte[] getUserKeyingMaterial(AlgorithmIdentifier keyAgreeAlgorithm)
        throws CMSException;

}