Sensitive data must be protected from eavesdropping and . 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 Transporting 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.
- Sensitive data must persist over an extended period of time (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.
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:
...
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.
| Code Block | ||
|---|---|---|
| ||
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 were sensitive, this example would also violate SER03-J. Do not serialize unencrypted sensitive data.
Noncompliant Code Example (Seal)
This noncompliant code example uses 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.
...
| Code Block | ||
|---|---|---|
| ||
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 the java.security.SignedObject class to sign an object when the integrity of the object 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.
...
| Code Block | ||
|---|---|---|
| ||
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);
}
|
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.
| Code Block | ||
|---|---|---|
| ||
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);
}
|
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.
Risk Assessment
Failure to sign and then seal objects during transit can lead to loss of object integrity or confidentiality.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
SER02-J | Medium | Probable | High | P4 | L3 |
Automated Detection
This rule is not amenable to static analysis in the general case.
| Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CodeSonar |
| JAVA.IO.INJ.ANDROID.MESSAGE | Android Message Injection (Java) |
Related Guidelines
Bibliography
[API 2014] |
Section 9.10, "Sealing Objects" | |
Chapter 11, "Object Serialization" | |
Item 64, "Use | |
Chapter 10, "Securing the Business Tier" |
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