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Wiki MarkupSensitive data must be protected from eavesdropping and malicious tampering during transit. An Obfuscated Transfer Object \[[Steel 2005|AA. Bibliography#Steel 05]\] that is strongly encrypted can protect data in exchanges that involve multiple business tiers or end user systems. This approach is known as _sealing_ the object. To guarantee object integrity, apply a digital signature to the sealed object. eavesdropping. All data that crosses a trust boundary must be protected from malicious tampering. An obfuscated transfer object [Steel 2005] that is strongly encrypted can protect data. This approach is known as sealing the object. To guarantee object integrity, apply a digital signature to the sealed object.

Sealing and signing objects is the preferred mechanism to secure data when

• Serializing or transporting sensitive data is necessaryTransporting sensitive data or serializing any data.
• A secure communication channel such as Secure Sockets Layer (SSL) is absent or is too costly for limited transactions.
• Some sensitive Sensitive data must persist over an extended period of time (e.g. on an external for example, on a hard drive).

Avoid using home-brewed cryptographic algorithms; such algorithms will almost certainly introduce unnecessary vulnerabilities. Applications that apply home-brewed "cryptography" in the readObject() and writeObject() methods are prime examples of anti-patterns. However, using existing cryptography libraries inside readObject() and writeObject() is perfrectly warranted.

Noncompliant Code Example

This noncompliant code example is capable of being serialized and transferred across different business tiers. Unfortunately, there are no safeguards against byte stream manipulation attacks while the binary data is in transit. Likewise, anyone can reverse engineer the stream data from its hexadecimal notation to reveal the data in the HashMap.

This rule applies to the intentional serialization of sensitive information. SER03-J. Do not serialize unencrypted sensitive data is meant to prevent the unintentional serialization of sensitive information.

Noncompliant Code Example

The code examples for this rule are all based on the following code example:

class SerializableMap<K,V> implements Serializable {
  final static long serialVersionUID = -2648720192864531932L;
  private HashMap<KMap<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) {
    // ...
  }
}

This code sample defines a serializable map, a method to populate the map with values, and a method to check the map for those values.

This noncompliant code example simply serializes then deserializes the map. Consequently, the map can be serialized and transferred across different business tiers. Unfortunately, the example lacks any safeguards against byte stream manipulation attacks while the binary data is in transit. Likewise, anyone can reverse-engineer the serialized stream data to recover the data in the HashMap. Anyone would also be able to tamper with the map and produce an object that made the deserializer crash or hang.

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);
}

If the data in the map is considered were sensitive, this example will would also violate SER03-J. Do not serialize unencrypted , sensitive data.

Compliant Solution

Noncompliant Code Example (Seal)

This noncompliant code example uses To provide message confidentiality, use the javax.crypto.SealedObject class to provide message confidentiality. This class encapsulates a serialized object and encrypts (or seals) it. A strong cryptographic algorithm that uses a secure cryptographic key and padding scheme must be employed to initialize the Cipher object parameter. The seal() and unseal() utility methods provide the encryption and decryption facilities respectively.

This noncompliant code example encrypts the map into a SealedObject, rendering the data inaccessible to prying eyes. However, the program fails to sign the data, rendering it impossible to authenticate.

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);
}

Noncompliant Code Example (Seal Then Sign)

This noncompliant code example uses In addition, use the java.security.SignedObject class to sign the an object , when the integrity of the object is to must be ensured. The two new arguments passed in to the SignedObject() method to sign the object are Signature and a private key derived from a KeyPair object. To verify the signature, a PublicKey as well as a Signature argument is passed to the SignedObject.verify() method. This enables the code to comply with SEC17-J. Create and sign a SignedObject before creating a SealedObject

This noncompliant code example signs the object as well as seals it. According to Abadi and Needham [Abadi 1996],

When a principal signs material that has already been encrypted, it should not be inferred that the principal knows the content of the message. On the other hand, it is proper to infer that the principal that signs a message and then encrypts it for privacy knows the content of the message.

Any malicious party can intercept the originally signed encrypted message from the originator, strip the signature, and add its own signature to the encrypted message. Both the malicious party and the receiver have no information about the contents of the original message because it is encrypted and then signed (it can be decrypted only after verifying the signature). The receiver has no way of confirming the sender's identity unless the legitimate sender's public key is obtained over a secure channel. One of the three Internal Telegraph and Telephone Consultative Committee (CCITT) X.509 standard protocols was susceptible to such an attack [CCITT 1988].

Because the signing occurs after the sealing, it cannot be assumed that the signer is the true originator of the object.

public static void main(String[] args)
                        throws IOException, GeneralSecurityException, 
                               ClassNotFoundException
class SerializableMap<K,V> implements Serializable {
  // other fields and methods...


  private SignedObject signedMap;

  public void sign(Signature sig, PrivateKey key)
    throws IOException, GeneralSecurityException {
    signedMap = new SignedObject( map, key 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 = null 
      new ObjectOutputStream(new FileOutputStream("data"));
  out.writeObject(signedMap);
  }out.close();

  public void unsign(Signature sig, PublicKey key)
    throws IOException, GeneralSecurityException, ClassNotFoundException {
  // 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(key), sig)) {
    throw new GeneralSecurityException("Map failed verification");
  }
  mapsealedMap = (HashMap<K,V>SealedObject) signedMap.getObject();

  // Unseal map
  cipher = Cipher.getInstance("AES");
  cipher.init(Cipher.DECRYPT_MODE, key);
  signedMapmap = null;(SerializableMap<String, Integer>) sealedMap.getObject(cipher);

  // Inspect map
  InspectMap(map);
}

Compliant Solution (Sign Then Seal)

This compliant solution correctly signs the object before sealing it. This approach provides a guarantee of authenticity to the object in addition to protection from man-in-the-middle attacks.

public static  }


  private SealedObject sealedMap;

  public void seal(Cipher cipher)
    throws IOException, IllegalBlockSizeException {
    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);

    // NowSerialize setmap
 the MapObjectOutputStream toout null= so
 that original data does not remainnew in cleartextObjectOutputStream(new FileOutputStream("data"));
    signedMap = null; 
  }

  public void unseal(Cipher cipher)
    throws IOException, GeneralSecurityException, ClassNotFoundException {
    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");
  }
  sealedMapmap = null; (SerializableMap<String, Integer>) signedMap.getObject();

  // Inspect map
  }InspectMap(map);
}

Exceptions

SER02-J-EX0: A reasonable use for signing a sealed object is to certify the authenticity of a sealed object passed from elsewhere. This use represents a commitment about the sealed object itself rather than about its content [Abadi 1996].

SER02-J-EX1: Signing and sealing is required only for objects that must cross a trust boundary. Objects that never leave the trust boundary need not be signed or sealed. For example, when an entire network is contained within a trust boundary, objects that never leave that network need not be signed or sealed. Another example is objects that are only sent down a signed binary stream.Finally, refrain from signing encrypted (sealed) data. (See guideline SEC17-J. Create and sign a SignedObject before creating a SealedObject.)

Risk Assessment

Failure to sign and /or then seal objects during transit can lead to loss of object integrity or confidentiality.

Automated Detection

Not This rule is not amenable to static analysis in the general case.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this guideline on the CERT website.

Bibliography

\[[API 2006|AA. Bibliography#API 06]\] 
\[[Gong 2003|AA. Bibliography#Gong 03]\] 9.10 Sealing Objects
\[[Harold 1999|AA. Bibliography#Harold 99]\] Chapter 11: Object Serialization, Sealed Objects 
\[[Neward 2004|AA. Bibliography#Neward 04]\] Item 64: Use SignedObject to provide integrity of Serialized objects and Item 65: Use SealedObject to provide confidentiality of Serializable objects
\[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE ID 319|http://cwe.mitre.org/data/definitions/319.html] "Cleartext Transmission of Sensitive Information"
\[[Steel 2005|AA. Bibliography#Steel 05]\] Chapter 10: Securing the Business Tier, Obfuscated Transfer Object

Related Guidelines

Bibliography

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Image Added Image Added Image AddedSEC15-J. Use SSLSockets rather than Sockets for secure data exchange      14. Platform Security (SEC)      SEC17-J. Create and sign a SignedObject before creating a SealedObject