/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions Copyright [year] [name of copyright owner]".
 *
 * Copyright 2006-2008 Sun Microsystems, Inc.
 * Portions Copyright 2010-2015 ForgeRock AS.
 */
package org.opends.server.extensions;



import java.security.MessageDigest;
import java.util.Arrays;
import java.util.Random;

import org.forgerock.i18n.LocalizableMessage;
import org.opends.server.admin.std.server.SaltedSHA256PasswordStorageSchemeCfg;
import org.opends.server.api.PasswordStorageScheme;
import org.forgerock.opendj.config.server.ConfigException;
import org.opends.server.core.DirectoryServer;
import org.forgerock.i18n.slf4j.LocalizedLogger;
import org.opends.server.types.*;
import org.forgerock.opendj.ldap.ResultCode;
import org.forgerock.opendj.ldap.ByteString;
import org.forgerock.opendj.ldap.ByteSequence;
import org.opends.server.util.Base64;

import static org.opends.messages.ExtensionMessages.*;
import static org.opends.server.extensions.ExtensionsConstants.*;
import static org.opends.server.util.StaticUtils.*;



/**
 * This class defines a Directory Server password storage scheme based on the
 * 256-bit SHA-2 algorithm defined in FIPS 180-2.  This is a one-way digest
 * algorithm so there is no way to retrieve the original clear-text version of
 * the password from the hashed value (although this means that it is not
 * suitable for things that need the clear-text password like DIGEST-MD5).  The
 * values that it generates are also salted, which protects against dictionary
 * attacks. It does this by generating a 64-bit random salt which is appended to
 * the clear-text value.  A SHA-2 hash is then generated based on this, the salt
 * is appended to the hash, and then the entire value is base64-encoded.
 */
public class SaltedSHA256PasswordStorageScheme
       extends PasswordStorageScheme<SaltedSHA256PasswordStorageSchemeCfg>
{
  private static final LocalizedLogger logger = LocalizedLogger.getLoggerForThisClass();

  /**
   * The fully-qualified name of this class.
   */
  private static final String CLASS_NAME =
       "org.opends.server.extensions.SaltedSHA256PasswordStorageScheme";



  /**
   * The number of bytes of random data to use as the salt when generating the
   * hashes.
   */
  private static final int NUM_SALT_BYTES = 8;

  /** Size of the dgiest in bytes. */
  private static final int SHA256_LENGTH = 256 / 8;

  /**
   * The message digest that will actually be used to generate the 256-bit SHA-2
   * hashes.
   */
  private MessageDigest messageDigest;

  /** The lock used to provide threadsafe access to the message digest. */
  private Object digestLock;

  /** The secure random number generator to use to generate the salt values. */
  private Random random;



  /**
   * Creates a new instance of this password storage scheme.  Note that no
   * initialization should be performed here, as all initialization should be
   * done in the <CODE>initializePasswordStorageScheme</CODE> method.
   */
  public SaltedSHA256PasswordStorageScheme()
  {
    super();
  }



  /** {@inheritDoc} */
  @Override
  public void initializePasswordStorageScheme(
                   SaltedSHA256PasswordStorageSchemeCfg configuration)
         throws ConfigException, InitializationException
  {
    try
    {
      messageDigest =
           MessageDigest.getInstance(MESSAGE_DIGEST_ALGORITHM_SHA_256);
    }
    catch (Exception e)
    {
      logger.traceException(e);

      LocalizableMessage message = ERR_PWSCHEME_CANNOT_INITIALIZE_MESSAGE_DIGEST.get(
          MESSAGE_DIGEST_ALGORITHM_SHA_256, e);
      throw new InitializationException(message, e);
    }


    digestLock = new Object();
    random     = new Random();
  }



  /** {@inheritDoc} */
  @Override
  public String getStorageSchemeName()
  {
    return STORAGE_SCHEME_NAME_SALTED_SHA_256;
  }



  /** {@inheritDoc} */
  @Override
  public ByteString encodePassword(ByteSequence plaintext)
         throws DirectoryException
  {
    int plainBytesLength = plaintext.length();
    byte[] saltBytes     = new byte[NUM_SALT_BYTES];
    byte[] plainPlusSalt = new byte[plainBytesLength + NUM_SALT_BYTES];

    plaintext.copyTo(plainPlusSalt);

    byte[] digestBytes;

    synchronized (digestLock)
    {
      try
      {
        // Generate the salt and put in the plain+salt array.
        random.nextBytes(saltBytes);
        System.arraycopy(saltBytes,0, plainPlusSalt, plainBytesLength,
                         NUM_SALT_BYTES);

        // Create the hash from the concatenated value.
        digestBytes = messageDigest.digest(plainPlusSalt);
      }
      catch (Exception e)
      {
        logger.traceException(e);

        LocalizableMessage message = ERR_PWSCHEME_CANNOT_ENCODE_PASSWORD.get(
            CLASS_NAME, getExceptionMessage(e));
        throw new DirectoryException(DirectoryServer.getServerErrorResultCode(),
                                     message, e);
      }
      finally
      {
        Arrays.fill(plainPlusSalt, (byte) 0);
      }
    }

    // Append the salt to the hashed value and base64-the whole thing.
    byte[] hashPlusSalt = new byte[digestBytes.length + NUM_SALT_BYTES];

    System.arraycopy(digestBytes, 0, hashPlusSalt, 0, digestBytes.length);
    System.arraycopy(saltBytes, 0, hashPlusSalt, digestBytes.length,
                     NUM_SALT_BYTES);

    return ByteString.valueOfUtf8(Base64.encode(hashPlusSalt));
  }



  /** {@inheritDoc} */
  @Override
  public ByteString encodePasswordWithScheme(ByteSequence plaintext)
         throws DirectoryException
  {
    StringBuilder buffer = new StringBuilder();
    buffer.append('{');
    buffer.append(STORAGE_SCHEME_NAME_SALTED_SHA_256);
    buffer.append('}');

    int plainBytesLength = plaintext.length();
    byte[] saltBytes     = new byte[NUM_SALT_BYTES];
    byte[] plainPlusSalt = new byte[plainBytesLength + NUM_SALT_BYTES];

    plaintext.copyTo(plainPlusSalt);

    byte[] digestBytes;

    synchronized (digestLock)
    {
      try
      {
        // Generate the salt and put in the plain+salt array.
        random.nextBytes(saltBytes);
        System.arraycopy(saltBytes,0, plainPlusSalt, plainBytesLength,
                         NUM_SALT_BYTES);

        // Create the hash from the concatenated value.
        digestBytes = messageDigest.digest(plainPlusSalt);
      }
      catch (Exception e)
      {
        logger.traceException(e);

        LocalizableMessage message = ERR_PWSCHEME_CANNOT_ENCODE_PASSWORD.get(
            CLASS_NAME, getExceptionMessage(e));
        throw new DirectoryException(DirectoryServer.getServerErrorResultCode(),
                                     message, e);
      }
      finally
      {
        Arrays.fill(plainPlusSalt, (byte) 0);
      }
    }

    // Append the salt to the hashed value and base64-the whole thing.
    byte[] hashPlusSalt = new byte[digestBytes.length + NUM_SALT_BYTES];

    System.arraycopy(digestBytes, 0, hashPlusSalt, 0, digestBytes.length);
    System.arraycopy(saltBytes, 0, hashPlusSalt, digestBytes.length,
                     NUM_SALT_BYTES);
    buffer.append(Base64.encode(hashPlusSalt));

    return ByteString.valueOfUtf8(buffer);
  }



  /** {@inheritDoc} */
  @Override
  public boolean passwordMatches(ByteSequence plaintextPassword,
                                 ByteSequence storedPassword)
  {
    // Base64-decode the stored value and take the first 256 bits
    // (SHA256_LENGTH) as the digest.
    byte[] saltBytes;
    byte[] digestBytes = new byte[SHA256_LENGTH];
    int saltLength = 0;

    try
    {
      byte[] decodedBytes = Base64.decode(storedPassword.toString());

      saltLength = decodedBytes.length - SHA256_LENGTH;
      if (saltLength <= 0)
      {
        logger.error(ERR_PWSCHEME_INVALID_BASE64_DECODED_STORED_PASSWORD, storedPassword);
        return false;
      }
      saltBytes = new byte[saltLength];
      System.arraycopy(decodedBytes, 0, digestBytes, 0, SHA256_LENGTH);
      System.arraycopy(decodedBytes, SHA256_LENGTH, saltBytes, 0,
                       saltLength);
    }
    catch (Exception e)
    {
      logger.traceException(e);
      logger.error(ERR_PWSCHEME_CANNOT_BASE64_DECODE_STORED_PASSWORD, storedPassword, e);
      return false;
    }


    // Use the salt to generate a digest based on the provided plain-text value.
    int plainBytesLength = plaintextPassword.length();
    byte[] plainPlusSalt = new byte[plainBytesLength + saltLength];
    plaintextPassword.copyTo(plainPlusSalt);
    System.arraycopy(saltBytes, 0,plainPlusSalt, plainBytesLength,
                     saltLength);

    byte[] userDigestBytes;

    synchronized (digestLock)
    {
      try
      {
        userDigestBytes = messageDigest.digest(plainPlusSalt);
      }
      catch (Exception e)
      {
        logger.traceException(e);

        return false;
      }
      finally
      {
        Arrays.fill(plainPlusSalt, (byte) 0);
      }
    }

    return Arrays.equals(digestBytes, userDigestBytes);
  }



  /** {@inheritDoc} */
  @Override
  public boolean supportsAuthPasswordSyntax()
  {
    // This storage scheme does support the authentication password syntax.
    return true;
  }



  /** {@inheritDoc} */
  @Override
  public String getAuthPasswordSchemeName()
  {
    return AUTH_PASSWORD_SCHEME_NAME_SALTED_SHA_256;
  }



  /** {@inheritDoc} */
  @Override
  public ByteString encodeAuthPassword(ByteSequence plaintext)
         throws DirectoryException
  {
    int plaintextLength = plaintext.length();
    byte[] saltBytes     = new byte[NUM_SALT_BYTES];
    byte[] plainPlusSalt = new byte[plaintextLength + NUM_SALT_BYTES];

    plaintext.copyTo(plainPlusSalt);

    byte[] digestBytes;

    synchronized (digestLock)
    {
      try
      {
        // Generate the salt and put in the plain+salt array.
        random.nextBytes(saltBytes);
        System.arraycopy(saltBytes,0, plainPlusSalt, plaintextLength,
                         NUM_SALT_BYTES);

        // Create the hash from the concatenated value.
        digestBytes = messageDigest.digest(plainPlusSalt);
      }
      catch (Exception e)
      {
        logger.traceException(e);

        LocalizableMessage message = ERR_PWSCHEME_CANNOT_ENCODE_PASSWORD.get(
            CLASS_NAME, getExceptionMessage(e));
        throw new DirectoryException(DirectoryServer.getServerErrorResultCode(),
                                     message, e);
      }
      finally
      {
        Arrays.fill(plainPlusSalt, (byte) 0);
      }
    }


    // Encode and return the value.
    StringBuilder authPWValue = new StringBuilder();
    authPWValue.append(AUTH_PASSWORD_SCHEME_NAME_SALTED_SHA_256);
    authPWValue.append('$');
    authPWValue.append(Base64.encode(saltBytes));
    authPWValue.append('$');
    authPWValue.append(Base64.encode(digestBytes));

    return ByteString.valueOfUtf8(authPWValue);
  }



  /** {@inheritDoc} */
  @Override
  public boolean authPasswordMatches(ByteSequence plaintextPassword,
                                     String authInfo, String authValue)
  {
    byte[] saltBytes;
    byte[] digestBytes;
    try
    {
      saltBytes   = Base64.decode(authInfo);
      digestBytes = Base64.decode(authValue);
    }
    catch (Exception e)
    {
      logger.traceException(e);

      return false;
    }


    int plainBytesLength = plaintextPassword.length();
    byte[] plainPlusSaltBytes = new byte[plainBytesLength + saltBytes.length];
    plaintextPassword.copyTo(plainPlusSaltBytes);
    System.arraycopy(saltBytes, 0, plainPlusSaltBytes, plainBytesLength,
                     saltBytes.length);

    synchronized (digestLock)
    {
      try
      {
        return Arrays.equals(digestBytes,
                                  messageDigest.digest(plainPlusSaltBytes));
      }
      finally
      {
        Arrays.fill(plainPlusSaltBytes, (byte) 0);
      }
    }
  }



  /** {@inheritDoc} */
  @Override
  public boolean isReversible()
  {
    return false;
  }



  /** {@inheritDoc} */
  @Override
  public ByteString getPlaintextValue(ByteSequence storedPassword)
         throws DirectoryException
  {
    LocalizableMessage message =
        ERR_PWSCHEME_NOT_REVERSIBLE.get(STORAGE_SCHEME_NAME_SALTED_SHA_256);
    throw new DirectoryException(ResultCode.CONSTRAINT_VIOLATION, message);
  }



  /** {@inheritDoc} */
  @Override
  public ByteString getAuthPasswordPlaintextValue(String authInfo,
                                                  String authValue)
         throws DirectoryException
  {
    LocalizableMessage message = ERR_PWSCHEME_NOT_REVERSIBLE.get(
        AUTH_PASSWORD_SCHEME_NAME_SALTED_SHA_256);
    throw new DirectoryException(ResultCode.CONSTRAINT_VIOLATION, message);
  }



  /** {@inheritDoc} */
  @Override
  public boolean isStorageSchemeSecure()
  {
    // SHA-2 should be considered secure.
    return true;
  }
}