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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.its.jcajce;

import java.security.PrivateKey;
import java.security.Provider;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;

import org.bouncycastle.its.operator.ETSIDataDecryptor;
import org.bouncycastle.jcajce.spec.IESKEMParameterSpec;
import org.bouncycastle.jcajce.util.JcaJceHelper;
import org.bouncycastle.jcajce.util.NamedJcaJceHelper;
import org.bouncycastle.jcajce.util.ProviderJcaJceHelper;
import org.bouncycastle.util.Arrays;


public class JcaETSIDataDecryptor
    implements ETSIDataDecryptor
{
    private final PrivateKey privateKey;
    private final JcaJceHelper helper;
    private final byte[] recipientHash;

    private SecretKey secretKey = null;

    JcaETSIDataDecryptor(PrivateKey recipientInfo, byte[] recipientHash, JcaJceHelper provider)
    {
        this.privateKey = recipientInfo;
        this.helper = provider;
        this.recipientHash = recipientHash;
    }

    public byte[] decrypt(byte[] wrappedKey, byte[] content, byte[] nonce)
    {
        try
        {
            Cipher etsiKem = helper.createCipher("ETSIKEMwithSHA256");
            etsiKem.init(Cipher.UNWRAP_MODE, privateKey, new IESKEMParameterSpec(recipientHash));

            // [ephemeral public key][encrypted key][tag]
            secretKey = (SecretKey)etsiKem.unwrap(wrappedKey, "AES", Cipher.SECRET_KEY);

            Cipher ccm = helper.createCipher("CCM");
            ccm.init(Cipher.DECRYPT_MODE, secretKey, ClassUtil.getGCMSpec(nonce, 128));
            return ccm.doFinal(content);
        }
        catch (Exception gex)
        {
            throw new RuntimeException(gex.getMessage(), gex);
        }
    }

    public byte[] getKey()
    {
        if (secretKey == null)
        {
            throw new IllegalStateException("no secret key recovered");
        }

        return secretKey.getEncoded();
    }


    public static Builder builder(PrivateKey privateKey, byte[] recipientHash)
    {
        return new Builder(privateKey, recipientHash);
    }

    public static class Builder
    {
        private JcaJceHelper provider;
        private final byte[] recipientHash;
        private final PrivateKey key;

        public Builder(PrivateKey key, byte[] recipientHash)
        {
            this.key = key;
            this.recipientHash = Arrays.clone(recipientHash);
        }

        public Builder provider(Provider provider)
        {
            this.provider = new ProviderJcaJceHelper(provider);
            return this;
        }

        public Builder provider(String provider)
        {
            this.provider = new NamedJcaJceHelper(provider);
            return this;
        }

        public JcaETSIDataDecryptor build()
        {
            return new JcaETSIDataDecryptor(key, recipientHash, provider);
        }
    }


}