SEC16-J. Sign and seal sensitive objects before transit

Sensitive data must be protected from eavesdropping and malicious tampering during transit. An Obfuscated Transfer Object [[Steel 2005]] 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.

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

• Serializing or transporting sensitive data is necessary
• A secure communication channel such as SSL is absent or is too costly for limited transactions
• Some sensitive data must persist over an extended period of time (e.g. on an external hard drive)

Avoid using home-brewed cryptographic algorithms; such algorithms almost certainly introduce unnecessary vulnerabilities. Applications that apply home-brewed "cryptography" in the readObject() and writeObject() methods are prime examples of anti-patterns.

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 unravel the HashMap containing sensitive social security numbers.

class SimpleObject<E,V> implements Serializable {
  final static long serialVersionUID = -2648720192864531932L;
  private HashMap<E,V> ssnMap;
  
  public SimpleObject() {
    ssnMap = new HashMap<E,V>();
  }

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

  public void setData(E key, V data)  {
    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<E,V> implements Serializable {
  final static long serialVersionUID = 2648720192864531932L;
  private HashMap<E,V> ssnMap;
  private SealedObject sealedSsnMap;
  private SignedObject signedSsnMap;
  
  public SignSealUtility() {
    ssnMap = new HashMap<E,V>();
  }

  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<E,V>)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<E,V>)signedSsnMap.getObject();
    }
  }

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

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 seal objects during transit can lead to loss of object integrity or confidentiality.

Automated Detection

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]]
[[Gong 2003]] 9.10 Sealing Objects
[[Harold 1999]] Chapter 11: Object Serialization, Sealed Objects
[[Neward 2004]] Item 64: Use SignedObject to provide integrity of Serialized objects and Item 65: Use SealedObject to provide confidentiality of Serializable objects
[[MITRE 2009]] CWE ID 319 "Cleartext Transmission of Sensitive Information"
[[Steel 2005]] Chapter 10: Securing the Business Tier, Obfuscated Transfer Object

SEC15-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