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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 1.5 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.
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package org.bouncycastle.cms.jcajce;

import java.io.IOException;
import java.security.AlgorithmParameters;
import java.security.GeneralSecurityException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.Provider;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.cert.CertificateEncodingException;
import java.security.cert.X509Certificate;
import java.security.spec.AlgorithmParameterSpec;
import java.util.ArrayList;
import java.util.List;

import javax.crypto.Cipher;
import javax.crypto.KeyAgreement;
import javax.crypto.SecretKey;

import org.bouncycastle.asn1.ASN1EncodableVector;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.DERSequence;
import org.bouncycastle.asn1.cms.KeyAgreeRecipientIdentifier;
import org.bouncycastle.asn1.cms.OriginatorPublicKey;
import org.bouncycastle.asn1.cms.RecipientEncryptedKey;
import org.bouncycastle.asn1.cms.RecipientKeyIdentifier;
import org.bouncycastle.asn1.cms.ecc.MQVuserKeyingMaterial;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.KeyAgreeRecipientInfoGenerator;
import org.bouncycastle.jcajce.spec.MQVParameterSpec;
import org.bouncycastle.jcajce.spec.UserKeyingMaterialSpec;
import org.bouncycastle.operator.DefaultSecretKeySizeProvider;
import org.bouncycastle.operator.GenericKey;
import org.bouncycastle.operator.SecretKeySizeProvider;
import org.bouncycastle.util.Arrays;

public class JceKeyAgreeRecipientInfoGenerator
    extends KeyAgreeRecipientInfoGenerator
{
    private SecretKeySizeProvider keySizeProvider = new DefaultSecretKeySizeProvider();

    private List recipientIDs = new ArrayList();
    private List recipientKeys = new ArrayList();
    private PublicKey senderPublicKey;
    private PrivateKey senderPrivateKey;

    private EnvelopedDataHelper helper = new EnvelopedDataHelper(new DefaultJcaJceExtHelper());
    private SecureRandom random;
    private KeyPair ephemeralKP;
    private byte[] userKeyingMaterial;

    public JceKeyAgreeRecipientInfoGenerator(ASN1ObjectIdentifier keyAgreementOID, PrivateKey senderPrivateKey, PublicKey senderPublicKey, ASN1ObjectIdentifier keyEncryptionOID)
    {
        super(keyAgreementOID, SubjectPublicKeyInfo.getInstance(senderPublicKey.getEncoded()), keyEncryptionOID);

        this.senderPublicKey = senderPublicKey;
        this.senderPrivateKey = senderPrivateKey;
    }

    public JceKeyAgreeRecipientInfoGenerator setUserKeyingMaterial(byte[] userKeyingMaterial)
    {
        this.userKeyingMaterial = Arrays.clone(userKeyingMaterial);

        return this;
    }

    public JceKeyAgreeRecipientInfoGenerator setProvider(Provider provider)
    {
        this.helper = new EnvelopedDataHelper(new ProviderJcaJceExtHelper(provider));

        return this;
    }

    public JceKeyAgreeRecipientInfoGenerator setProvider(String providerName)
    {
        this.helper = new EnvelopedDataHelper(new NamedJcaJceExtHelper(providerName));

        return this;
    }

    public JceKeyAgreeRecipientInfoGenerator setSecureRandom(SecureRandom random)
    {
        this.random = random;

        return this;
    }

    /**
     * Add a recipient based on the passed in certificate's public key and its issuer and serial number.
     * 
     * @param recipientCert recipient's certificate
     * @return the current instance.
     * @throws CertificateEncodingException  if the necessary data cannot be extracted from the certificate.
     */
    public JceKeyAgreeRecipientInfoGenerator addRecipient(X509Certificate recipientCert)
        throws CertificateEncodingException
    {
        recipientIDs.add(new KeyAgreeRecipientIdentifier(CMSUtils.getIssuerAndSerialNumber(recipientCert)));
        recipientKeys.add(recipientCert.getPublicKey());

        return this;
    }

    /**
     * Add a recipient identified by the passed in subjectKeyID and the for the passed in public key.
     *
     * @param subjectKeyID identifier actual recipient will use to match the private key.
     * @param publicKey the public key for encrypting the secret key.
     * @return the current instance.
     * @throws CertificateEncodingException
     */
    public JceKeyAgreeRecipientInfoGenerator addRecipient(byte[] subjectKeyID, PublicKey publicKey)
        throws CertificateEncodingException
    {
        recipientIDs.add(new KeyAgreeRecipientIdentifier(new RecipientKeyIdentifier(subjectKeyID)));
        recipientKeys.add(publicKey);

        return this;
    }

    public ASN1Sequence generateRecipientEncryptedKeys(AlgorithmIdentifier keyAgreeAlgorithm, AlgorithmIdentifier keyEncryptionAlgorithm, GenericKey contentEncryptionKey)
        throws CMSException
    {
        if (recipientIDs.isEmpty())
        {
            throw new CMSException("No recipients associated with generator - use addRecipient()");
        }

        init(keyAgreeAlgorithm.getAlgorithm());

        PrivateKey senderPrivateKey = this.senderPrivateKey;

        ASN1ObjectIdentifier keyAgreementOID = keyAgreeAlgorithm.getAlgorithm();

        ASN1EncodableVector recipientEncryptedKeys = new ASN1EncodableVector();
        for (int i = 0; i != recipientIDs.size(); i++)
        {
            PublicKey recipientPublicKey = (PublicKey)recipientKeys.get(i);
            KeyAgreeRecipientIdentifier karId = (KeyAgreeRecipientIdentifier)recipientIDs.get(i);

            try
            {
                AlgorithmParameterSpec agreementParamSpec;

                if (CMSUtils.isMQV(keyAgreementOID))
                {
                    agreementParamSpec = new MQVParameterSpec(ephemeralKP, recipientPublicKey, userKeyingMaterial);
                }
                else if (CMSUtils.isEC(keyAgreementOID))
                {
                    byte[] ukmKeyingMaterial = ecc_cms_Generator.generateKDFMaterial(keyEncryptionAlgorithm, keySizeProvider.getKeySize(keyEncryptionAlgorithm.getAlgorithm()), userKeyingMaterial);

                    agreementParamSpec = new UserKeyingMaterialSpec(ukmKeyingMaterial);
                }
                else if (CMSUtils.isRFC2631(keyAgreementOID))
                {
                    if (userKeyingMaterial != null)
                    {
                        agreementParamSpec = new UserKeyingMaterialSpec(userKeyingMaterial);
                    }
                    else
                    {
                        if (keyAgreementOID.equals(PKCSObjectIdentifiers.id_alg_SSDH))
                        {
                            throw new CMSException("User keying material must be set for static keys.");
                        }
                        agreementParamSpec = null;
                    }
                }
                else
                {
                    throw new CMSException("Unknown key agreement algorithm: " + keyAgreementOID);
                }

                // Use key agreement to choose a wrap key for this recipient
                KeyAgreement keyAgreement = helper.createKeyAgreement(keyAgreementOID);
                keyAgreement.init(senderPrivateKey, agreementParamSpec, random);
                keyAgreement.doPhase(recipientPublicKey, true);

                SecretKey keyEncryptionKey = keyAgreement.generateSecret(keyEncryptionAlgorithm.getAlgorithm().getId());

                // Wrap the content encryption key with the agreement key
                Cipher keyEncryptionCipher = helper.createCipher(keyEncryptionAlgorithm.getAlgorithm());

                keyEncryptionCipher.init(Cipher.WRAP_MODE, keyEncryptionKey, random);

                byte[] encryptedKeyBytes = keyEncryptionCipher.wrap(helper.getJceKey(contentEncryptionKey));

                ASN1OctetString encryptedKey = new DEROctetString(encryptedKeyBytes);

                recipientEncryptedKeys.add(new RecipientEncryptedKey(karId, encryptedKey));
            }
            catch (GeneralSecurityException e)
            {
                throw new CMSException("Cannot perform agreement step: " + e.getMessage(), e);
            }
        }

        return new DERSequence(recipientEncryptedKeys);
    }

    protected byte[] getUserKeyingMaterial(AlgorithmIdentifier keyAgreeAlg)
        throws CMSException
    {
        init(keyAgreeAlg.getAlgorithm());

        if (ephemeralKP != null)
        {
            OriginatorPublicKey originatorPublicKey = createOriginatorPublicKey(SubjectPublicKeyInfo.getInstance(ephemeralKP.getPublic().getEncoded()));

            try
            {
                if (userKeyingMaterial != null)
                {
                    return new MQVuserKeyingMaterial(originatorPublicKey, new DEROctetString(userKeyingMaterial)).getEncoded();
                }
                else
                {
                    return new MQVuserKeyingMaterial(originatorPublicKey, null).getEncoded();
                }
            }
            catch (IOException e)
            {
                throw new CMSException("unable to encode user keying material: " + e.getMessage(), e);
            }
        }

        return userKeyingMaterial;
    }

    private void init(ASN1ObjectIdentifier keyAgreementOID)
        throws CMSException
    {
        if (random == null)
        {
            random = new SecureRandom();
        }

        if (CMSUtils.isMQV(keyAgreementOID))
        {
            if (ephemeralKP == null)
            {
                try
                {
                    SubjectPublicKeyInfo pubInfo = SubjectPublicKeyInfo.getInstance(senderPublicKey.getEncoded());

                    AlgorithmParameters ecAlgParams = helper.createAlgorithmParameters(keyAgreementOID);

                    ecAlgParams.init(pubInfo.getAlgorithm().getParameters().toASN1Primitive().getEncoded());

                    KeyPairGenerator ephemKPG = helper.createKeyPairGenerator(keyAgreementOID);

                    ephemKPG.initialize(ecAlgParams.getParameterSpec(AlgorithmParameterSpec.class), random);

                    ephemeralKP = ephemKPG.generateKeyPair();
                }
                catch (Exception e)
                {
                    throw new CMSException(
                        "cannot determine MQV ephemeral key pair parameters from public key: " + e, e);
                }
            }
        }
    }

    private static KeyMaterialGenerator ecc_cms_Generator = new RFC5753KeyMaterialGenerator();
}