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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.bc;

import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.pkcs.PBKDF2Params;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.cms.CMSException;
import org.bouncycastle.cms.PasswordRecipient;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.PBEParametersGenerator;
import org.bouncycastle.crypto.Wrapper;
import org.bouncycastle.crypto.generators.PKCS5S2ParametersGenerator;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;

/**
 * the RecipientInfo class for a recipient who has been sent a message
 * encrypted using a password.
 */
public abstract class BcPasswordRecipient
    implements PasswordRecipient
{
    private final char[] password;

    private int schemeID = PasswordRecipient.PKCS5_SCHEME2_UTF8;

    BcPasswordRecipient(
        char[] password)
    {
        this.password = password;
    }

    public BcPasswordRecipient setPasswordConversionScheme(int schemeID)
    {
        this.schemeID = schemeID;

        return this;
    }

    protected KeyParameter extractSecretKey(AlgorithmIdentifier keyEncryptionAlgorithm, AlgorithmIdentifier contentEncryptionAlgorithm, byte[] derivedKey, byte[] encryptedContentEncryptionKey)
        throws CMSException
    {
        Wrapper keyEncryptionCipher = EnvelopedDataHelper.createRFC3211Wrapper(keyEncryptionAlgorithm.getAlgorithm());

        keyEncryptionCipher.init(false, new ParametersWithIV(new KeyParameter(derivedKey), ASN1OctetString.getInstance(keyEncryptionAlgorithm.getParameters()).getOctets()));

        try
        {
            return new KeyParameter(keyEncryptionCipher.unwrap(encryptedContentEncryptionKey, 0, encryptedContentEncryptionKey.length));
        }
        catch (InvalidCipherTextException e)
        {
            throw new CMSException("unable to unwrap key: " + e.getMessage(), e);
        }
    }

    public byte[] calculateDerivedKey(int schemeID, AlgorithmIdentifier derivationAlgorithm, int keySize)
        throws CMSException
    {
        PBKDF2Params params = PBKDF2Params.getInstance(derivationAlgorithm.getParameters());
        byte[] encodedPassword = (schemeID == PasswordRecipient.PKCS5_SCHEME2) ? PBEParametersGenerator.PKCS5PasswordToBytes(password) : PBEParametersGenerator.PKCS5PasswordToUTF8Bytes(password);

        try
        {
            PKCS5S2ParametersGenerator gen = new PKCS5S2ParametersGenerator(EnvelopedDataHelper.getPRF(params.getPrf()));

            gen.init(encodedPassword, params.getSalt(), params.getIterationCount().intValue());

            return ((KeyParameter)gen.generateDerivedParameters(keySize)).getKey();
        }
        catch (Exception e)
        {
            throw new CMSException("exception creating derived key: " + e.getMessage(), e);
        }
    }

    public int getPasswordConversionScheme()
    {
        return schemeID;
    }

    public char[] getPassword()
    {
        return password;
    }
}