This CKS practice question tests your understanding of supply chain security. 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.
Developer A runs 'cosign verify --key cosign.pub myregistry/myimage:tag' and receives an error: 'No signatures found'. Developer B previously ran 'cosign sign --key cosign.key myregistry/myimage:tag'. What is the most likely cause of the verification failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The signing command failed to push the signature to the registry
Option A is correct. The error 'No signatures found' indicates that the image does not have a signature attached to it. This could happen if the signing command did not push the signature to the registry. Option B is irrelevant because the image tag exists. Option C is incorrect because the signing command uses the private key. Option D is incorrect; the verification command uses the public key, but the error is about missing signatures, not key mismatch.
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 image tag does not exist in the registry
Why it's wrong here
If the image tag did not exist, the cosign command would return a different error.
✓
The signing command failed to push the signature to the registry
Why this is correct
If the signature is not pushed, the verify command will find no signatures.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Developer B used a different private key to sign than the public key used for verification
Why it's wrong here
This would cause a signature verification failure, not 'No signatures found'.
✗
Developer A used the public key instead of the private key
Why it's wrong here
Verification uses the public key; the error is about missing signatures, not key type.
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.
Trap categories for this question
Command / output trap
If the image tag did not exist, the cosign command would return a different error.
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 CKS 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 CKS NAT questions on configuration and troubleshooting.
Supply Chain Security — This question tests Supply Chain Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The signing command failed to push the signature to the registry — Option A is correct. The error 'No signatures found' indicates that the image does not have a signature attached to it. This could happen if the signing command did not push the signature to the registry. Option B is irrelevant because the image tag exists. Option C is incorrect because the signing command uses the private key. Option D is incorrect; the verification command uses the public key, but the error is about missing signatures, not key mismatch.
What should I do if I get this CKS 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 CKS NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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