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 * regarding copyright ownership.  The ASF licenses this file   *
 * to you under the Apache License, Version 2.0 (the            *
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 * software distributed under the License is distributed on an  *
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY       *
 * KIND, either express or implied.  See the License for the    *
 * specific language governing permissions and limitations      *
 * under the License.                                           *
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package org.apache.james.transport;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.PrivateKey;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertStore;
import java.security.cert.CertStoreException;
import java.security.cert.CertificateEncodingException;
import java.security.cert.CertificateException;
import java.security.cert.CollectionCertStoreParameters;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;

import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;

import org.bouncycastle.cert.jcajce.JcaCertStore;
import org.bouncycastle.cms.SignerInfoGenerator;
import org.bouncycastle.cms.jcajce.JcaSimpleSignerInfoGeneratorBuilder;
import org.bouncycastle.mail.smime.SMIMEException;
import org.bouncycastle.mail.smime.SMIMESignedGenerator;
import org.bouncycastle.operator.OperatorCreationException;

/**
 * <p>Loads a {@link java.security.KeyStore} in memory and keeps it ready for the
 * cryptographic activity.</p>
 * <p>It has the role of being a simpler intermediate to the crypto libraries.
 * Uses specifically the <a href="http://www.bouncycastle.org/">Legion of the Bouncy Castle</a>
 * libraries, particularly for the SMIME activity.</p>
 * @version CVS $Revision$ $Date$
 * @since 3.0
 */
public class SMIMEKeyHolder implements KeyHolder {

    private final JcaCertStore jcaCertStore;

    /**
     * Returns the default keystore type as specified in the Java security properties file,
     * or the string "jks" (acronym for "Java keystore") if no such property exists.
     * @return The defaultType, issuing a <CODE>KeyStore.getDefaultType()</CODE>.
     */
    public static String getDefaultType() {
        return KeyStore.getDefaultType();
    }
    
    /**
     * Holds value of property privateKey.
     */
    private final PrivateKey privateKey;
    
    /**
     * Holds value of property certificate.
     */
    private final X509Certificate certificate;
    
    /**
     * Holds value of property certStore.
     */
    private final CertStore certStore;
    
    /**
     * Creates a new instance of <CODE>KeyHolder</CODE> using {@link java.security.KeyStore} related parameters.
     * @param keyStoreFileName The (absolute) file name of the .keystore file to load the keystore from.
     * @param keyStorePassword The (optional) password used to check the integrity of the keystore.
     *      If given, it is used to check the integrity of the keystore data,
     *      otherwise, if null, the integrity of the keystore is not checked.
     * @param keyAlias The alias name of the key.
     *      If missing (is null) and if there is only one key in the keystore, will default to it.
     * @param keyAliasPassword The password of the alias for recovering the key.
     *      If missing (is null) will default to <I>keyStorePassword</I>. At least one of the passwords must be provided.
     * @param keyStoreType The type of keystore.
     *      If missing (is null) will default to the keystore type as specified in the Java security properties file,
     *      or the string "jks" (acronym for "Java keystore") if no such property exists.
     * @throws java.security.KeyStoreException Thrown when the <I>keyAlias</I> is specified and not found,
     *      or is not specified and either no alias is found or more than one is found.
     * @see java.security.KeyStore#getDefaultType
     * @see java.security.KeyStore#getInstance(String)
     * @see java.security.KeyStore#load
     * @see java.security.KeyStore#getKey
     * @see java.security.KeyStore#getCertificate
     */
    public SMIMEKeyHolder(String keyStoreFileName, String keyStorePassword, String keyAlias, String keyAliasPassword, String keyStoreType)
    throws KeyStoreException, IOException, NoSuchAlgorithmException, InvalidAlgorithmParameterException,
    CertificateException, UnrecoverableKeyException, NoSuchProviderException {
        
        try {
            InitJCE.init();
        } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
            NoSuchProviderException ex = new NoSuchProviderException("Error during cryptography provider initialization. Has bcprov-jdkxx-yyy.jar been copied in the lib directory or installed in the system?");
            ex.initCause(e);
            throw ex;
        }

        if (keyStoreType == null) {
            keyStoreType = KeyStore.getDefaultType();
        }
        
        KeyStore keyStore = KeyStore.getInstance(keyStoreType);
        keyStore.load(new BufferedInputStream(new FileInputStream(keyStoreFileName)), keyStorePassword.toCharArray());
        
        Enumeration<String> aliases = keyStore.aliases();
        if (keyAlias == null) {
            if (aliases.hasMoreElements()) {
                keyAlias = aliases.nextElement();
            } else {
                throw new KeyStoreException("No alias was found in keystore.");
            }
            if (aliases.hasMoreElements()) {
                throw new KeyStoreException("No <keyAlias> was given and more than one alias was found in keystore.");
                
            }
        }
        
        if (keyAliasPassword == null) {
            keyAliasPassword = keyStorePassword;
        }
        
        this.privateKey = (PrivateKey) keyStore.getKey(keyAlias, keyAliasPassword.toCharArray());
        if (this.privateKey == null) {
            throw new KeyStoreException("The \"" + keyAlias + "\" PrivateKey alias was not found in keystore.");
        }
        
        this.certificate = (X509Certificate) keyStore.getCertificate(keyAlias);
        if (this.certificate == null) {
            throw new KeyStoreException("The \"" + keyAlias + "\" X509Certificate alias was not found in keystore.");
        }
        java.security.cert.Certificate[] certificateChain = keyStore.getCertificateChain(keyAlias);
        ArrayList<java.security.cert.Certificate> certList = new ArrayList<>();
        if (certificateChain == null) {
            certList.add(this.certificate);
        } else {
            Collections.addAll(certList, certificateChain);
        }
        
        // create a CertStore containing the certificates we want carried
        // in the signature
        this.certStore = CertStore.getInstance("Collection",
        new CollectionCertStoreParameters(certList), "BC");

        jcaCertStore = new JcaCertStore(certList);

    }
    
    /**
     * Getter for property privateKey.
     * @return Value of property privateKey.
     */
    public PrivateKey getPrivateKey() {
        return this.privateKey;
    }
    
    /**
     * Getter for property certificate.
     * @return Value of property certificate.
     */
    public X509Certificate getCertificate() {
        return this.certificate;
    }
    
    /**
     * Getter for property certStore.
     * @return Value of property certStore.
     */
    public CertStore getCertStore() {
        return this.certStore;
    }

    /**
     * Creates an <CODE>SMIMESignedGenerator</CODE>. Includes a signer private key and certificate,
     * and a pool of certs and cerls (if any) to go with the signature.
     * @return The generated SMIMESignedGenerator.
     */
    public SMIMESignedGenerator createGenerator() throws CertStoreException, SMIMEException, OperatorCreationException,
        CertificateEncodingException {
        
        // create the generator for creating an smime/signed message
        SMIMESignedGenerator generator = new SMIMESignedGenerator();
        
        // add a signer to the generator - this specifies we are using SHA1
        // the encryption algorithm used is taken from the key
        SignerInfoGenerator signerInfoGenerator = new JcaSimpleSignerInfoGeneratorBuilder()
            .setProvider("BC")
            .build("SHA1withRSA", privateKey, certificate);
        generator.addSignerInfoGenerator(signerInfoGenerator);
        
        // add our pool of certs and cerls (if any) to go with the signature
        generator.addCertificates(jcaCertStore);
        
        return generator;
        
    }
    
    /**
     * Generates a signed MimeMultipart from a MimeMessage.
     * @param message The message to sign.
     * @return The signed <CODE>MimeMultipart</CODE>.
     */    
    @Override
    public MimeMultipart generate(MimeMessage message) throws CertStoreException, NoSuchAlgorithmException, NoSuchProviderException,
        SMIMEException, OperatorCreationException, CertificateEncodingException {
        
        // create the generator for creating an smime/signed MimeMultipart
        SMIMESignedGenerator generator = createGenerator();
        
        // do it
        return generator.generate(message);
        
    }
    
    /**
     * Generates a signed MimeMultipart from a MimeBodyPart.
     * @param content The content to sign.
     * @return The signed <CODE>MimeMultipart</CODE>.
     */
    @Override
    public MimeMultipart generate(MimeBodyPart content) throws CertStoreException, NoSuchAlgorithmException, NoSuchProviderException,
        SMIMEException, OperatorCreationException, CertificateEncodingException {
        
        // create the generator for creating an smime/signed MimeMultipart
        SMIMESignedGenerator generator = createGenerator();
        
        // do it
        return generator.generate(content);
        
    }

    /**
     * Extracts the signer <I>distinguished name</I> (DN) from an <CODE>X509Certificate</CODE>.
     * @param certificate The certificate to extract the information from.
     * @return The requested information.
     */    
    public static String getSignerDistinguishedName(X509Certificate certificate) {
        
        return certificate.getSubjectDN().toString();
        
    }
    
    /**
     * Extracts the signer <I>common name</I> (CN=) from an <CODE>X509Certificate</CODE> <I>distinguished name</I>.
     * @param certificate The certificate to extract the information from.
     * @return The requested information.
     * @see #getSignerDistinguishedName(X509Certificate)
     */    
    public static String getSignerCN(X509Certificate certificate) {
        
        return extractAttribute(certificate.getSubjectDN().toString(), "CN=");
        
    }

    /**
     * Extracts the signer <I>email address</I> (EMAILADDRESS=) from an <CODE>X509Certificate</CODE> <I>distinguished name</I>.
     * @param certificate The certificate to extract the information from.
     * @return The requested information.
     * @see #getSignerDistinguishedName(X509Certificate)
     */    
    public static String getSignerAddress(X509Certificate certificate) {
        
        return extractAttribute(certificate.getSubjectDN().toString(), "EMAILADDRESS=");
        
    }
    
    /**
     * Getter for property signerDistinguishedName.
     * @return Value of property signerDistinguishedName.
     * @see #getSignerDistinguishedName(X509Certificate)
     */
    @Override
    public String getSignerDistinguishedName() {
        return getSignerDistinguishedName(getCertificate());
    }

    /**
     * Getter for property signerCN.
     * @return Value of property signerCN.
     * @see #getSignerCN(X509Certificate)
     */
    @Override
    public String getSignerCN() {
        return getSignerCN(getCertificate());
    }

    /**
     * Getter for property signerAddress.
     * @return Value of property signerMailAddress.
     * @see #getSignerAddress(X509Certificate)
     */
    @Override
    public String getSignerAddress() {
        return getSignerAddress(getCertificate());
    }
    
   private static String extractAttribute(String DistinguishedName, String attributeName) {
        
        int i = DistinguishedName.indexOf(attributeName);
        
        if (i < 0) {
            return null;
        }
        
        i += attributeName.length();
        int j = DistinguishedName.indexOf(",", i);
        
        if (j - 1 <= 0) {
            return null;
        }
        
        return DistinguishedName.substring(i, j).trim();
        
    }
    
}
