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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.operator.jcajce;

import java.io.InputStream;
import java.security.Provider;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.cryptopro.GOST28147Parameters;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.jcajce.io.CipherInputStream;
import org.bouncycastle.jcajce.spec.GOST28147ParameterSpec;
import org.bouncycastle.jcajce.util.DefaultJcaJceHelper;
import org.bouncycastle.jcajce.util.JcaJceHelper;
import org.bouncycastle.jcajce.util.NamedJcaJceHelper;
import org.bouncycastle.jcajce.util.ProviderJcaJceHelper;
import org.bouncycastle.operator.InputDecryptor;
import org.bouncycastle.operator.InputDecryptorProvider;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.util.Arrays;

/**
 * A generic decryptor provider for IETF style algorithms.
 */
public class JceInputDecryptorProviderBuilder
{
    private JcaJceHelper helper = new DefaultJcaJceHelper();

    public JceInputDecryptorProviderBuilder()
    {
    }

    public JceInputDecryptorProviderBuilder setProvider(Provider provider)
    {
        this.helper = new ProviderJcaJceHelper(provider);

        return this;
    }

    public JceInputDecryptorProviderBuilder setProvider(String providerName)
    {
        this.helper = new NamedJcaJceHelper(providerName);

        return this;
    }

    /**
     * Build a decryptor provider which will use the passed in bytes for the symmetric key.
     *
     * @param keyBytes bytes representing the key to use.
     * @return an decryptor provider.
     */
    public InputDecryptorProvider build(byte[] keyBytes)
    {
        final byte[] encKeyBytes = Arrays.clone(keyBytes);

        return new InputDecryptorProvider()
        {
            private Cipher cipher;
            private AlgorithmIdentifier encryptionAlg;

            public InputDecryptor get(final AlgorithmIdentifier algorithmIdentifier)
                throws OperatorCreationException
            {
                encryptionAlg = algorithmIdentifier;

                ASN1ObjectIdentifier algorithm = algorithmIdentifier.getAlgorithm();

                try
                {
                    cipher = helper.createCipher(algorithm.getId());
                    SecretKey key = new SecretKeySpec(encKeyBytes, algorithm.getId());
                    
                    ASN1Encodable encParams = algorithmIdentifier.getParameters();

                    if (encParams instanceof ASN1OctetString)
                    {
                        cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(ASN1OctetString.getInstance(encParams).getOctets()));
                    }
                    else
                    {
                        // TODO: at the moment it's just GOST, but...
                        GOST28147Parameters gParams = GOST28147Parameters.getInstance(encParams);

                        cipher.init(Cipher.DECRYPT_MODE, key, new GOST28147ParameterSpec(gParams.getEncryptionParamSet(), gParams.getIV()));
                    }
                }
                catch (Exception e)
                {
                    throw new OperatorCreationException("unable to create InputDecryptor: " + e.getMessage(), e);
                }

                return new InputDecryptor()
                {
                    public AlgorithmIdentifier getAlgorithmIdentifier()
                    {
                        return encryptionAlg;
                    }

                    public InputStream getInputStream(InputStream input)
                    {
                        return new CipherInputStream(input, cipher);
                    }
                };
            }
        };
    }
}