/*
    * Copyright 2009-2010 Capgemini
    * Licensed under the Apache License, Version 2.0 (the "License"); 
    * you may not use this file except in compliance with the License. 
    * You may obtain a copy of the License at 
    * 
    * http://www.apache.org/licenses/LICENSE-2.0 
    * 
    * Unless required by applicable law or agreed to in writing, 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. 
   * 
   */
  package net.sourceforge.statelessfilter.utils;
  
  import java.io.UnsupportedEncodingException;
  import java.security.InvalidKeyException;
  import java.security.NoSuchAlgorithmException;
  import java.security.SignatureException;
  
  import javax.crypto.Mac;
  import javax.crypto.spec.SecretKeySpec;
  
  import org.apache.commons.codec.binary.Hex;
  
  /**
   * HMAC utility methods.
   */
  public final class HmacUtils {
  
  	private static final String HMAC_SHA1_ALGORITHM = "HmacSHA1";
  
  	/**
  	 * Private constructor
  	 */
  	private HmacUtils() {
  	}
  
  	public static String calculateRFC2104HMAC(String data, String key)
  			throws SignatureException {
  		String result;
  
  		if (data == null || key == null) {
  			throw new IllegalArgumentException(
  					"data and key must be not null. data:" + data + " key: "
  							+ key == null ? "null" : "not null");
  		}
  		// Get an hmac_sha1 key from the raw key bytes
  		byte[] keyBytes = key.getBytes();
  		SecretKeySpec signingKey = new SecretKeySpec(keyBytes,
  				HMAC_SHA1_ALGORITHM);
  
  		try {
  			// Get an hmac_sha1 Mac instance and initialize with the signing key
  			Mac mac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
  			mac.init(signingKey);
  
  			// Compute the hmac on input data bytes
  			byte[] rawHmac = mac.doFinal(data.getBytes());
  
  			// Convert raw bytes to Hex
  			byte[] hexBytes = new Hex().encode(rawHmac);
  
  			// Covert array of Hex bytes to a String
  			result = new String(hexBytes, "ISO-8859-1");
  		} catch (InvalidKeyException e) {
  			throw new SignatureException("Failed to generate HMAC : "
  					+ e.getMessage(), e);
  		} catch (NoSuchAlgorithmException e) {
  			throw new SignatureException("Failed to generate HMAC : "
  					+ e.getMessage(), e);
  		} catch (UnsupportedEncodingException e) {
  			throw new SignatureException("Failed to generate HMAC : "
  					+ e.getMessage(), e);
  		}
  
  		return result;
  	}
  
  	public static String signRFC2104HMAC(String data, String key,
  			String separator) throws SignatureException {
  
  		String hash = HmacUtils.calculateRFC2104HMAC(data, key);
  		String signedData = data + separator + hash;
  
  		return signedData;
  	}
  
  	public static String verifyRFC2104HMAC(String data, String key,
  			String separator) throws SignatureException {
  		int idx = data.lastIndexOf(separator);
  		if (idx >= 0) {
  			String unsignedValue = data.substring(0, idx);
  
  			String hash = data.substring(idx + 1);
  
  			if (hash.equals(calculateRFC2104HMAC(unsignedValue, key))) {
 				return unsignedValue;
 			}
 		}
 		return null;
 	}
 }