SEC08-J. Sign and seal sensitive objects before transit

It is imperative that sensitive data should be protected from eavesdropping and malicious tampering during transit. An Obfuscated Transfer Object [[Steel 05]] can be used to encrypt data in exchanges that involve multiple business tiers or end user systems. This design pattern can further be supplemented to provide signature capabilities for guaranteeing object integrity.

Signing and sealing objects takes preference over other similar measures when:

• The data is sensitive but its serialization or transportation is necessary
• A secure communication channel such as SSL is absent or is a costly operation for a short interaction
• Some sensitive data needs to persist over an extended period of time (for example, on an external hard drive)
• Implementing custom cryptographic algorithms such as in the readObject and writeObject methods can leave the application exposed to security holes. It is advisable to not reinvent the broken wheel.

Noncompliant Code Example

The code in this noncompliant 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 unroll the HashMap containing sensitive social security numbers.

class SimpleObject implements Serializable {
  final long serialVersionUID = -2648720192864531932L;
  private HashMap ssnMap;
  private SealedObject sealedSsnMap;

  public SimpleObject() {
    ssnMap = new HashMap();
  }

  public Object getdata(Object key) throws Exception {
    return ssnMap.get(key);
  }

  public void setData(Object key, Object data) throws Exception {
    ssnMap.put(key, data);
  }
}

Compliant Solution

To provide message confidentiality, use the javax.crypto.SealedObject class. 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.

In addition, use the sign and unsign utility methods when the integrity of the object is to 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.

class SignSealUtility implements Serializable {
  final long serialVersionUID = 2648720192864531932L;
  private HashMap ssnMap;
  private SealedObject sealedSsnMap;
  private SignedObject signedSsnMap;
  
  public SignSealUtility() {
    ssnMap = new HashMap();
  }

  public void seal(Cipher cipher) throws Exception {
    sealedSsnMap = new SealedObject(ssnMap, cipher);
    // Now set the Map to null so that original data does not remain in cleartext
    ssnMap = null; 
  }

  public void unseal(Cipher cipher) throws Exception {
    ssnMap = (HashMap)sealedSsnMap.getObject(cipher);
  }
  
  public void sign(Signature sig, PrivateKey key) throws Exception {
    signedSsnMap = new SignedObject(ssnMap, key, sig);
    ssnMap = null;
  }

  public void unsign(Signature sig, PublicKey key) throws Exception {
    if(signedSsnMap.verify(key, sig)) {
      ssnMap = (HashMap)signedSsnMap.getObject();
    }
  }

  public Object getdata(Object key) throws Exception {
    return ssnMap.get(key);
  }
 
  public void setData(Object key, Object data) throws Exception {
    ssnMap.put(key, data);
  }
}

Note that the compliant solution throws a general Exception to limit the minutest of the information leaks that relate to the cryptographic implementation. Finally, one should refrain from signing encrypted (sealed) data. (See SEC09-J. Create and sign a SignedObject before creating a SealedObject)

Risk Assessment

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

Automated Detection

TODO

Related Vulnerabilities

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

References

[[API 06]]
[[Steel 05]] Chapter 10: Securing the Business Tier, Obfuscated Transfer Object
[[Gong 03]] 9.10 Sealing Objects
[[Harold 99]] Chapter 11: Object Serialization, Sealed Objects
[[Neward 04]] Item 64: Use SignedObject to provide integrity of Serialized objects and Item 65: Use SealedObject to provide confidentiality of Serializable objects
[[MITRE 09]] CWE ID 319 "Cleartext Transmission of Sensitive Information"

SEC07-J. Minimize accessibility of classes and their members      00. Security (SEC)      SEC09-J. Create and sign a SignedObject before creating a SealedObject