The answer is to set 'PasswordAuthentication no' in /etc/ssh/sshd_config on the EC2 instance. This configuration directly disables the SSH daemon’s ability to accept password-based logins, forcing all connections to use SSH key pairs for authentication. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of host-level security controls versus network-level or IAM-based controls—a common trap is confusing security group rules (which filter traffic, not authentication methods) with SSH configuration. Remember that while security groups control *who can reach* the instance, only the sshd_config file controls *how they authenticate* once connected. A useful memory tip: think of it as "keys in the config, not in the cloud"—the enforcement happens inside the EC2 instance’s operating system, not through AWS services like IAM or Instance Connect.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 security engineer needs to ensure that an EC2 instance can only be accessed using SSH key pairs, not passwords. Which configuration is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set 'PasswordAuthentication no' in /etc/ssh/sshd_config on the EC2 instance
Option B is correct because disabling password authentication in the SSH daemon configuration ensures only key-based authentication is allowed. Option A is wrong because security groups control network access, not authentication method. Option C is wrong because IAM roles do not affect SSH authentication. Option D is wrong because EC2 Instance Connect is an alternative, not a method to enforce key-only.
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.
✗
Use EC2 Instance Connect instead of SSH
Why it's wrong here
EC2 Instance Connect uses SSH keys or browser-based SSH, but does not enforce key-only on the instance.
✓
Set 'PasswordAuthentication no' in /etc/ssh/sshd_config on the EC2 instance
Why this is correct
This disables password-based SSH login, enforcing key-based authentication.
Related concept
Static NAT maps one inside address to one outside address.
✗
Attach an IAM role to the instance that denies password-based access
Why it's wrong here
IAM roles do not control SSH authentication; they control AWS API permissions.
✗
Configure the security group to allow SSH only from specific IP addresses
Why it's wrong here
Security groups control network access, not authentication method.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
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 SCS-C02 NAT questions on configuration and troubleshooting.
Infrastructure Security — This question tests Infrastructure Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Set 'PasswordAuthentication no' in /etc/ssh/sshd_config on the EC2 instance — Option B is correct because disabling password authentication in the SSH daemon configuration ensures only key-based authentication is allowed. Option A is wrong because security groups control network access, not authentication method. Option C is wrong because IAM roles do not affect SSH authentication. Option D is wrong because EC2 Instance Connect is an alternative, not a method to enforce key-only.
What should I do if I get this SCS-C02 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 SCS-C02 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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