BcKeyTransRecipient.java

package org.bouncycastle.cms.bc;

import java.util.Set;

import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.cms.AbstractRecipient;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.KeyTransRecipient;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.operator.AsymmetricKeyUnwrapper;
import org.bouncycastle.operator.OperatorException;
import org.bouncycastle.operator.bc.BcRSAAsymmetricKeyUnwrapper;

public abstract class BcKeyTransRecipient
    extends AbstractRecipient
    implements KeyTransRecipient
{
    private AsymmetricKeyParameter recipientKey;

    public BcKeyTransRecipient(AsymmetricKeyParameter recipientKey)
    {
        this.recipientKey = recipientKey;
    }

    /**
     * Set the content-encryption algorithms this recipient is willing to unwrap a key for. When set, an
     * attempt to recover content protected under any other algorithm is rejected, mitigating an attacker
     * substituting a weaker content-encryption algorithm into the recipient info.
     *
     * @param allowedContentAlgorithms the set of permitted content-encryption algorithm OIDs.
     * @return this recipient.
     */
    public BcKeyTransRecipient setAllowedContentAlgorithms(Set<ASN1ObjectIdentifier> allowedContentAlgorithms)
    {
        setAllowedContentAlgorithmSet(allowedContentAlgorithms);

        return this;
    }

    protected CipherParameters extractSecretKey(AlgorithmIdentifier keyEncryptionAlgorithm, AlgorithmIdentifier encryptedKeyAlgorithm, byte[] encryptedEncryptionKey)
        throws CMSException
    {
        checkContentAlgorithm(encryptedKeyAlgorithm);

        AsymmetricKeyUnwrapper unwrapper = new BcRSAAsymmetricKeyUnwrapper(keyEncryptionAlgorithm, recipientKey);

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