Understanding Secure Coding Concepts

Secure coding concepts are important for application developers to understand. Additionally, IT security managers who manage development projects should understand these concepts, even if they aren’t writing the code. If you’re planning to take the SY0-501 exam, you should have a basic understanding of some common secure application development and deployment concepts.

For example, can you answer this practice test question?

Q. Developers have created an application that users can download and install on their computers. Management wants to provide users with a reliable method of verifying that the application has not been modified. Which of the following methods provides the BEST solution?

A. Code signing

B. Input validation

C. Code obfuscation

D. Stored procedures

E. Normalization

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation are available at the end of this post.

Cryptographic Techniques

In general, sensitive data is often encrypted to prevent the unauthorized disclosure of data. If an application is accessing any sensitive data, developers need to ensure that this access doesn’t result in inadvertent data exposure. For example, if an application accesses encrypted data on a different server, the application needs to ensure that the data is encrypted while in transit.

Applications need to decrypt data before processing it. When done processing the data, applications need to encrypt the data before storing it. Additionally, applications need to ensure that all remnants of the data are flushed from memory.

Certificates are used for various purposes such as authenticating users and computers. They can also be used to authenticate and validate software code. As an example, developers can purchase a certificate and associate it with an application or code. This code signing process provides a digital signature for the code and the certificate includes a hash of the code. This provides two benefits. First, the certificate identifies the author. Second, the hash verifies the code has not been modified. If malware changes the code, the hash no longer matches, alerting the user that the code has been modified.

Code Reuse and SDKs

Developers are encouraged to reuse code whenever possible. As an example, imagine a developer created code for a web application to create, modify, and authenticate users and this code has been in use for a year. The code has gone through internal testing and has survived the use within the application. Instead of creating brand-new code for a new application, it’s best to use this tested code. Code reuse saves time and helps prevent the introduction of new bugs.

However, when reusing code, developers should ensure that they are using all the code that they copy into another application. As an example, imagine a developer has created a module that has three purposes: create users, modify users, and authenticate users. While working on a new application, he realizes he needs a module that will authenticate users. If he simply copies the entire module into the new application, it creates dead code. Dead code is code that is never executed or used. In this example, the copied code to create and modify users isn’t used in the new application, so it is dead code.

Logic errors can also create dead code. For example, imagine a function tests the value of a variable called Donuts. If Donuts has a value (such as 12), it squares it. If Donuts is null (a value of nothing), it returns an error and exits the function.

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Next, the function checks to see if Donuts is null and if so, it prints a message in an error log. Do you see the error? The code to print to an error log never executes. If Donuts is null, the previous check exited the function, so the second check never occurs. This logic error creates the dead code.

Another popular method of code reuse is the use of third-party libraries. As an example, JavaScript is a rich, interpreted language used by many web applications. Netscape originally developed it and it was ultimately standardized as an open source language.

Software development kits (SDKs) are like third-party libraries, but they are typically tied to a single vendor. For example, if you’re creating an Android app, you can use the Android SDK. It includes software tools that will help you create apps for Android-based devices.

Code Obfuscation

Developers often spend a lot of time developing code. If it is JavaScript, it is rather easy for other developers to just copy the code and use it. One way to slow this down is with an obfuscation/camouflage method.

Obfuscation attempts to make something unclear or difficult to understand. Code obfuscation (or code camouflage) attempts to make the code unreadable. It does things like rename variables, replace numbers with expressions, replace strings of characters with hexadecimal codes, and remove comments. For example, a meaningful variable of strFirstName might be renamed to 94mdiwl, and the number 11 might be changed to 0xF01B – 0x73 – 0xEF9D (which still results in the decimal number 11).

It’s worth noting that most security experts reject security through obscurity as a reliable method of maintaining security. Similarly, code obfuscation might make the code difficult to understand by most people. However, it’s still possible for someone with skills to dissect the code.

Q. Developers have created an application that users can download and install on their computers. Management wants to provide users with a reliable method of verifying that the application has not been modified. Which of the following methods provides the BEST solution?

A. Code signing

B. Input validation

C. Code obfuscation

D. Stored procedures

E. Normalization

Answer is A. Code signing provides a digital signature for the code and verifies the publisher of the code and verifies that it hasn’t been modified since the publisher released it.

None of the other answers verify the application hasn’t been modified.

Input validation verifies data is valid before using it.

Code obfuscation makes the code more difficult to read.

Stored procedures are used with SQL databases and can be used for input validation.

Normalization refers to organizing tables and columns in a database to reduce redundant data and improve overall database performance.

See Chapter 7 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on secure coding concepts.