In AP Cybersecurity, secure coding is the practice of writing applications with security built in from the start, using principles like secure by design and security by default plus techniques like user input sanitization to block attacks before they happen.
Secure coding is the habit of writing software that defends itself instead of leaving holes for attackers to find. Two big ideas drive it. Secure by design means security is a design principle, not a bolt-on feature you add at the end. Companies take ownership of customer security outcomes, build products that actually meet security needs, and embrace transparency about security news and updates (EK 5.5.A.1, EK 5.5.A.2). Security by default means a product ships in its safest configuration out of the box, so a user doesn't have to be a security expert to stay protected.
On the technical side, secure coding leans hard on user input sanitization. When someone types into an app, the program wraps that input in special control characters like the single quote ('), double quote ("), and semicolon (;) to process it (EK 5.5.B.1). The problem? An attacker can sneak those same characters into a form field to manipulate the system. Secure coding fixes this with a verification function that checks input against expected criteria and strips out malicious control characters before they ever reach the back end (EK 5.5.B.2).
Secure coding lives in Unit 5: Securing Applications and Data, specifically topic 5.5 Protecting Applications. It backs two learning objectives: AP Cybersecurity 5.5.A (identifying secure by design and security by default) and AP Cybersecurity 5.5.B (explaining how input sanitization protects applications). The reason it matters for the whole course is that most real attacks exploit sloppy code, not broken encryption. If you understand secure coding, you understand the root cause behind injection attacks, web vulnerabilities, and a chunk of the threats covered across the exam. It's the prevention side of the same coin as the attacks in other units.
Keep studying AP Cybersecurity Unit 5
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view galleryCross-Site Scripting (Unit 5)
XSS is exactly what secure coding stops. An attacker injects malicious script through an input field, and the fix is sanitizing input to strip control characters. Secure coding is the defense, XSS is the attack that gets through when you skip it.
Code Review (Unit 5)
Code review is how teams check that secure coding actually happened. Writing secure code is the goal, and a second set of eyes reviewing it catches the input-handling mistakes one programmer missed.
Security by Default (Unit 5)
This is the configuration twin of secure coding. Even perfectly written code can be deployed insecurely, so shipping a product locked-down by default makes sure good code doesn't get undone by a risky setting.
Expect multiple-choice stems that hand you a scenario and ask which secure coding principle applies. A question might describe a company baking security into the design phase and ask you to name it (secure by design), or show a login form vulnerable to manipulation and ask which technique fixes it (input sanitization). You may need to identify the three control characters by name (single quote, double quote, semicolon) or explain what a sanitization function does. The skill being tested is recognizing prevention built into the software itself, not after-the-fact monitoring. Tie any input-handling question back to stripping or validating control characters before processing.
Secure coding is the act of writing safe code in the first place. Code review is the process of inspecting code (yours or someone else's) to catch mistakes, including security flaws. One is the writing, the other is the checking. They work together, but they're different steps.
Secure coding builds security into software from the design phase instead of patching it on later.
Secure by design means security is a design principle and includes taking ownership of customer security outcomes and embracing transparency (EK 5.5.A.2).
Control characters are the single quote, double quote, and semicolon, and attackers abuse them to manipulate a system (EK 5.5.B.1).
Input sanitization uses a verification function to check that input meets expected criteria and to remove malicious control characters (EK 5.5.B.2).
Secure coding is the prevention behind attacks like cross-site scripting, which succeed when input isn't sanitized.
It's the practice of writing applications with security built in from the start, guided by secure by design and security by default and supported by input sanitization that strips malicious control characters. It maps to topic 5.5 in Unit 5.
No. Secure coding is writing the safe code yourself, while code review is the separate step of inspecting code to catch flaws. They complement each other, but the exam treats them as distinct concepts.
The single quote ('), the double quote ("), and the semicolon (;). Programs use them to encase user input, and attackers exploit them to manipulate the system, which is why sanitization removes them (EK 5.5.B.1).
A verification function checks that user input meets the expected criteria and removes any malicious control characters before the input reaches the back end (EK 5.5.B.2). This blocks injection-style attacks like cross-site scripting.
Secure by design means security is a planned principle throughout product development, including the design phase. Security by default means the product ships in its safest configuration so users are protected without having to change settings.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.