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Spongy Castle is a package-rename (org.bouncycastle.* to org.spongycastle.*) of Bouncy Castle intended for Android. Android ships with a stripped-down version of Bouncy Castle - this causes classloader collisions if you try to add an alternative (updated/complete) Bouncy Castle jar. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5.

There is a newer version: 1.46.99.3-UNOFFICIAL-ROBERTO-RELEASE

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package org.spongycastle.cms.jcajce;

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

import javax.crypto.SecretKey;

import org.spongycastle.asn1.x509.AlgorithmIdentifier;
import org.spongycastle.cms.CMSException;
import org.spongycastle.cms.KEKRecipient;
import org.spongycastle.jcajce.DefaultJcaJceHelper;
import org.spongycastle.jcajce.NamedJcaJceHelper;
import org.spongycastle.jcajce.ProviderJcaJceHelper;
import org.spongycastle.operator.OperatorException;
import org.spongycastle.operator.SymmetricKeyUnwrapper;

public abstract class JceKEKRecipient
    implements KEKRecipient
{
    private SecretKey recipientKey;

    protected EnvelopedDataHelper helper = new EnvelopedDataHelper(new DefaultJcaJceHelper());
    protected EnvelopedDataHelper contentHelper = helper;

    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 ProviderJcaJceHelper(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 NamedJcaJceHelper(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 ProviderJcaJceHelper(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 NamedJcaJceHelper(providerName));

        return this;
    }

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

        try
        {
            return CMSUtils.getJceKey(unwrapper.generateUnwrappedKey(contentEncryptionAlgorithm, encryptedContentEncryptionKey));
        }
        catch (OperatorException e)
        {
            throw new CMSException("exception unwrapping key: " + e.getMessage(), e);
        }
    }
}