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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.jcajce;

import java.security.Key;
import java.security.Provider;

import javax.crypto.SecretKey;

import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.KEKRecipient;
import org.bouncycastle.operator.OperatorException;
import org.bouncycastle.operator.SymmetricKeyUnwrapper;

public abstract class JceKEKRecipient
    implements KEKRecipient
{
    private SecretKey recipientKey;

    protected EnvelopedDataHelper helper = new EnvelopedDataHelper(new DefaultJcaJceExtHelper());
    protected EnvelopedDataHelper contentHelper = helper;
    protected boolean validateKeySize = false;

    public JceKEKRecipient(SecretKey recipientKey)
    {
        this.recipientKey = recipientKey;
    }

    /**
     * Set the provider to use for key recovery and content processing.
     *
     * @param provider provider to use.
     * @return this recipient.
     */
    public JceKEKRecipient setProvider(Provider provider)
    {
        this.helper = new EnvelopedDataHelper(new ProviderJcaJceExtHelper(provider));
        this.contentHelper = helper;

        return this;
    }

    /**
     * Set the provider to use for key recovery and content processing.
     *
     * @param providerName the name of the provider to use.
     * @return this recipient.
     */
    public JceKEKRecipient setProvider(String providerName)
    {
        this.helper = new EnvelopedDataHelper(new NamedJcaJceExtHelper(providerName));
        this.contentHelper = helper;

        return this;
    }

    /**
     * Set the provider to use for content processing.
     *
     * @param provider the provider to use.
     * @return this recipient.
     */
    public JceKEKRecipient setContentProvider(Provider provider)
    {
        this.contentHelper = new EnvelopedDataHelper(new ProviderJcaJceExtHelper(provider));

        return this;
    }

    /**
     * Set the provider to use for content processing.
     *
     * @param providerName the name of the provider to use.
     * @return this recipient.
     */
    public JceKEKRecipient setContentProvider(String providerName)
    {
        this.contentHelper = new EnvelopedDataHelper(new NamedJcaJceExtHelper(providerName));

        return this;
    }

    /**
     * Set validation of retrieved key sizes against the algorithm parameters for the encrypted key where possible - default is off.
     * 
     * This setting will not have any affect if the encryption algorithm in the recipient does not specify a particular key size, or
     * if the unwrapper is a HSM and the byte encoding of the unwrapped secret key is not available.
     * 
     * @param doValidate true if unwrapped key's should be validated against the content encryption algorithm, false otherwise.
     * @return this recipient.
     */
    public JceKEKRecipient setKeySizeValidation(boolean doValidate)
    {
        this.validateKeySize = doValidate;

        return this;
    }

    protected Key extractSecretKey(AlgorithmIdentifier keyEncryptionAlgorithm, AlgorithmIdentifier encryptedKeyAlgorithm, byte[] encryptedContentEncryptionKey)
        throws CMSException
    {
        SymmetricKeyUnwrapper unwrapper = helper.createSymmetricUnwrapper(keyEncryptionAlgorithm, recipientKey);

        try
        {
            Key key =  helper.getJceKey(encryptedKeyAlgorithm.getAlgorithm(), unwrapper.generateUnwrappedKey(encryptedKeyAlgorithm, encryptedContentEncryptionKey));

            if (validateKeySize)
            {
                helper.keySizeCheck(encryptedKeyAlgorithm, key);
            }

            return key;
        }
        catch (OperatorException e)
        {
            throw new CMSException("exception unwrapping key: " + e.getMessage(), e);
        }
    }
}