The correct answer is DKIM, or DomainKeys Identified Mail, because it is the only email authentication protocol that cryptographically signs each outgoing message with a private key, allowing the recipient’s mail server to verify both the sender’s domain and that the email body has not been altered in transit. Unlike SPF, which only checks the sending IP address, or DMARC, which builds on SPF and DKIM for policy enforcement, DKIM’s digital signature ensures integrity and non-repudiation. On the Computer Hacking Forensic Investigator CHFI exam, this question tests your understanding of how forensic investigators trace email spoofing and tampering; a common trap is confusing DKIM’s signature-based verification with SPF’s IP-based check. To remember, think “DKIM = Digital Key Integrity Mail” — the signature proves the domain and that the message hasn’t been doctored.
CHFI Application, Email and Cloud Forensics Practice Question
This CHFI practice question tests your understanding of application, email and cloud forensics. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which of the following email authentication protocols uses a digital signature to verify the sender's domain and that the email has not been tampered with?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DKIM
DKIM (DomainKeys Identified Mail) uses a digital signature to authenticate the email's domain and integrity.
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.
✗
DMARC
Why it's wrong here
DMARC is a policy framework that uses SPF and DKIM, but does not itself provide a signature.
✓
DKIM
Why this is correct
DKIM adds a digital signature to the email headers, allowing verification of the domain and message integrity.
Related concept
Static NAT maps one inside address to one outside address.
✗
SPF
Why it's wrong here
SPF (Sender Policy Framework) checks the sending server's IP against a list, not a digital signature.
✗
STARTTLS
Why it's wrong here
STARTTLS is used to upgrade a plaintext connection to an encrypted one, not for authentication.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI 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 CHFI NAT questions on configuration and troubleshooting.
Application, Email and Cloud Forensics — This question tests Application, Email and Cloud Forensics — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: DKIM — DKIM (DomainKeys Identified Mail) uses a digital signature to authenticate the email's domain and integrity.
What should I do if I get this CHFI 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 CHFI 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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