The strongest indicator of spoofing is that the DKIM signature domain is evil.com, not paypal.com. This is because DKIM (DomainKeys Identified Mail) cryptographically signs an email with a private key, and the public key is published in the DNS of the domain listed in the d= tag of the DKIM-Signature header. When the signing domain (evil.com) does not match the domain in the email’s From address (paypal.com), it reveals that the message was not authorized by the claimed sender, making it a classic dkim domain mismatch email spoofing scenario. On the CHFI exam, this concept tests your ability to analyze email headers for forensic evidence of forgery; a common trap is focusing on the IP address or the Received chain instead of the cryptographic mismatch. Remember the memory tip: “The d= domain must match the From domain—if they differ, the email is a spoofed offender.”
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.
During an email forensics investigation, an analyst examines headers and sees `Received: from mail.evil.com (192.168.1.100) by mail.victim.com` followed by `DKIM-Signature: v=1; a=rsa-sha256; d=evil.com; s=selector; bh=...; h=...; b=...`. The email claims to be from support@paypal.com. Which finding is the strongest indicator of spoofing?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DKIM signature domain is evil.com, not paypal.com
The DKIM-Signature domain (evil.com) does not match the claimed sender domain (paypal.com). This mismatch indicates the email is likely spoofed.
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.
✗
The email was received via SMTP
Why it's wrong here
SMTP is the standard protocol for email delivery; its presence is normal.
✗
The email lacks a SPF record in the header
Why it's wrong here
While SPF failure is also an indicator, the question asks for the strongest among the options. The DKIM domain mismatch is more definitive.
✗
The email originated from IP 192.168.1.100
Why it's wrong here
The IP itself is not conclusive; it could be a legitimate mail server.
✓
The DKIM signature domain is evil.com, not paypal.com
Why this is correct
A valid DKIM signature for paypal.com should have d=paypal.com. The mismatch is a strong spoofing indicator.
Related concept
Static NAT maps one inside address to one outside address.
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: The DKIM signature domain is evil.com, not paypal.com — The DKIM-Signature domain (evil.com) does not match the claimed sender domain (paypal.com). This mismatch indicates the email is likely spoofed.
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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