The answer is second preimage resistance, along with preimage resistance and collision resistance, as the three necessary properties of a hash function for digital signatures. These properties ensure non-repudiation by making it computationally infeasible to reverse the hash, find a different input that produces the same hash, or find any two distinct inputs that hash to the same value. On the CISSP exam, this concept tests your understanding of how digital signatures guarantee integrity and non-repudiation, often appearing in questions about cryptographic controls or secure communications. A common trap is confusing determinism—which is a functional characteristic, not a security property—with these core requirements. Remember that a hash function must be one-way and unique in output to prevent forgery. For a quick memory tip, think of the three properties as the “three pillars of hash security”: preimage, second preimage, and collision resistance—all essential to prevent an attacker from undermining a digital signature’s trust.
CISSP Security Architecture and Engineering Practice Question
This CISSP practice question tests your understanding of security architecture and engineering. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is implementing a digital signature system to ensure non-repudiation. The security architect must select a hash function that meets the required security properties. Which THREE of the following are necessary properties for the hash function?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Preimage resistance
A hash function must be preimage resistant (unable to invert), second preimage resistant (cannot find another input with the same hash), and collision resistant (cannot find two inputs with the same hash). Reversibility is not a property of hash functions—they are one-way. Determinism is inherent to all hash functions but is not a security property.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Preimage resistance
Why this is correct
Correct: Preimage resistance ensures that given a hash, it is computationally infeasible to find any input that produces that hash.
Related concept
Static NAT maps one inside address to one outside address.
✗
Reversibility
Why it's wrong here
Incorrect: Hash functions are designed to be one-way; reversibility is not a property and would compromise security.
✓
Collision resistance
Why this is correct
Correct: Collision resistance ensures that it is infeasible to find two distinct inputs that produce the same hash.
Related concept
Static NAT maps one inside address to one outside address.
✓
Second preimage resistance
Why this is correct
Correct: Second preimage resistance ensures that given an input, it is infeasible to find a different input that produces the same hash.
Related concept
Static NAT maps one inside address to one outside address.
✗
Determinism
Why it's wrong here
Incorrect: While hash functions are deterministic, this is an inherent characteristic, not a required security property.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISSP NAT questions on configuration and troubleshooting.
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Preimage resistance — A hash function must be preimage resistant (unable to invert), second preimage resistant (cannot find another input with the same hash), and collision resistant (cannot find two inputs with the same hash). Reversibility is not a property of hash functions—they are one-way. Determinism is inherent to all hash functions but is not a security property.
What should I do if I get this CISSP question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISSP NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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