java基础每日学习20131029--序列化

原则4.1 敏感对象发送出信任区域前进行签名并加密

说明：敏感数据传输过程中要防止窃取和非法篡改。使用安全的加密算法给数据加密可以防止数据被窃取。而对数据加上数字签名则可以防止数据被非法篡改。在以下场景中，需要加密和数字签名的机制保证数据安全：
1）序列化或传输敏感数据；2）无SSL传输通道或者代价太高；3）敏感数据需要长久保存；应该要避免使用私有加密算法，以免引入更多的漏洞。应用程序在readObject()和writeObject()方法中使用私有加密算法是典型的反例。本规则的错误示例代码和推荐做法都是基于下面的代码来说明:

class SerializableMap<K, V> implements Serializable 
{ 
    final static long serialVersionUID = -2648720192864531932L; 
    
    private Map<K, V> map; 
    
    public SerializableMap() 
    { 
        map = new HashMap<K, V>(); 
    } 
    
    public Object getData(K key) 
    { 
        return map.get(key); 
    } 
    
    public void setData(K key, V data) 
    { 
        map.put(key, data); 
    } 
} 

public class MapSerializer 
{ 
    public static SerializableMap<String, Integer> buildMap() 
    { 
        SerializableMap<String, Integer> map = new SerializableMap<String, Integer>(); 
        map.setData("John Doe", new Integer(123456789)); 
        map.setData("Richard Roe", new Integer(246813579)); 
        return map; 
    } 
    
    public static void InspectMap(SerializableMap<String, Integer> map) 
    { 
        System.out.println("John Doe's number is " + map.getData("John Doe")); 
        System.out.println("Richard Roe's number is " 
                + map.getData("Richard Roe")); 
    } 
    
    public static void main(String[] args) 
    { 
        // ... 
    } 
} 
错误示例1：未做任何安全防护 
public static void main(String[] args) throws IOException, 
    ClassNotFoundException 
{ 
    // Build map 
    SerializableMap<String, Integer> map = buildMap(); 
    // Serialize map 
    ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data")); 
    out.writeObject(map); 
    out.close(); 
    // Deserialize map 
    ObjectInputStream in = new ObjectInputStream(new FileInputStream("data")); 
    map = (SerializableMap<String, Integer>) in.readObject(); 
    in.close(); 
    // Inspect map 
    InspectMap(map);       
} 
错误示例2：只加密 
public static void main(String[] args) throws IOException, 
        GeneralSecurityException, ClassNotFoundException 
{ 
    // Build map 
    SerializableMap<String, Integer> map = buildMap(); 
    // Generate sealing key & seal map 
    KeyGenerator generator; 
    generator = KeyGenerator.getInstance("AES"); 
    generator.init(new SecureRandom()); 
    Key key = generator.generateKey(); 
    Cipher cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.ENCRYPT_MODE, key); 
    SealedObject sealedMap = new SealedObject(map, cipher); 
    // Serialize map 
    ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data")); 
    out.writeObject(sealedMap); 
    out.close(); 
    // Deserialize map 
    ObjectInputStream in = new ObjectInputStream(new FileInputStream("data")); 
    sealedMap = (SealedObject) in.readObject(); 
    in.close(); 
    // Unseal map 
    cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.DECRYPT_MODE, key); 
    map = (SerializableMap<String, Integer>) sealedMap.getObject(cipher); 
    // Inspect map 
    InspectMap(map); 
} 
错误示例3：先加密后签名 
public static void main(String[] args) throws IOException, GeneralSecurityException, ClassNotFoundException 
{ 
    // Build map 
    SerializableMap<String, Integer> map = buildMap(); 
    // Generate sealing key & seal map 
    KeyGenerator generator; 
    generator = KeyGenerator.getInstance("AES"); 
    generator.init(new SecureRandom()); 
    Key key = generator.generateKey(); 
    Cipher cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.ENCRYPT_MODE, key); 
    SealedObject sealedMap = new SealedObject(map, cipher); 
    // Generate signing public/private key pair & sign map 
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA"); 
    KeyPair kp = kpg.generateKeyPair(); 
    Signature sig = Signature.getInstance("SHA1withDSA"); 
    SignedObject signedMap = new SignedObject(sealedMap, kp.getPrivate(), sig); 
        // Serialize map 
    ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data")); 
    out.writeObject(signedMap); 
    out.close(); 
    // Deserialize map 
    ObjectInputStream in = new ObjectInputStream(new FileInputStream("data")); 
    signedMap = (SignedObject) in.readObject(); 
    in.close(); 
    // Verify signature and retrieve map 
    if (!signedMap.verify(kp.getPublic(), sig)) 
    { 
        throw new GeneralSecurityException("Map failed verification"); 
    } 
    sealedMap = (SealedObject) signedMap.getObject(); 
    // Unseal map 
    cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.DECRYPT_MODE, key); 
    map = (SerializableMap<String, Integer>) sealedMap.getObject(cipher); 
    // Inspect map 
    InspectMap(map); 
} 
这段代码先对数据进行加密，然后再对加密后的数据进行签名。这样做无法保证签名来自数据的原始来源。 
任何恶意的第三方可以截获原始加密签名后的数据，剔除原始的签名，并对密封的数据加上自己的签名。 
这样的话，即使恶意第三方无法获取原始的数据内容，正常的接收者也无法得到原始的数据。 
推荐做法：先签名后加密 
public static void main(String[] args) throws IOException, GeneralSecurityException, ClassNotFoundException 
{ 
    // Build map 
    SerializableMap<String, Integer> map = buildMap(); 
    // Generate signing public/private key pair & sign map 
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA"); 
    KeyPair kp = kpg.generateKeyPair(); 
    Signature sig = Signature.getInstance("SHA1withDSA"); 
    SignedObject signedMap = new SignedObject(map, kp.getPrivate(), sig); 
    // Generate sealing key & seal map 
    KeyGenerator generator; 
    generator = KeyGenerator.getInstance("AES"); 
    generator.init(new SecureRandom()); 
    Key key = generator.generateKey(); 
    Cipher cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.ENCRYPT_MODE, key); 
    SealedObject sealedMap = new SealedObject(signedMap, cipher); 
    // Serialize map 
    ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream( 
                "data")); 
    out.writeObject(sealedMap); 
    out.close(); 
    // Deserialize map 
    ObjectInputStream in = new ObjectInputStream(new FileInputStream("data")); 
    sealedMap = (SealedObject) in.readObject(); 
    in.close(); 
    // Unseal map cipher = Cipher.getInstance("AES"); 
    cipher.init(Cipher.DECRYPT_MODE, key); 
    signedMap = (SignedObject) sealedMap.getObject(cipher); 
    // Verify signature and retrieve map 
    if (!signedMap.verify(kp.getPublic(), sig)) 
    { 
        throw new GeneralSecurityException("Map failed verification"); 
    } 
    map = (SerializableMap<String, Integer>) signedMap.getObject(); 
    // Inspect map 
    InspectMap(map); 
} 
先签名后加密，既能保证数据的真实可靠性，又能防止“中间人攻击”(man-in-middle attacks)。