Question 80 of 997

Supply Chain Security →hardMultiple ChoiceObjective-mapped

Troubleshoot Cosign Verify: No Signatures Found

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.

A
The image tag does not exist in the registry
Why wrong: If the image tag did not exist, the cosign command would return a different error.
B
The signing command failed to push the signature to the registry
If the signature is not pushed, the verify command will find no signatures.
C
Developer B used a different private key to sign than the public key used for verification
Why wrong: This would cause a signature verification failure, not 'No signatures found'.
D
Developer A used the public key instead of the private key
Why wrong: Verification uses the public key; the error is about missing signatures, not key type.

Full breakdown with real-world context →

Answer choices

Why each option matters

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

The error 'No signatures found' indicates that the verification process could not locate any signature associated with the image in the registry. Since Developer B attempted to sign the image with 'cosign sign', the most likely cause is that the signing command failed to push the signature artifact (typically stored as a separate tag like 'myimage:sha256-<digest>.sig' in the same registry) to the registry. Without the signature being successfully uploaded, the 'cosign verify' command finds nothing to validate against the provided public key.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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
Read the scenario before looking for a memorised answer.
✗
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: answer the scenario, not the keyword

The CKS exam often tests the distinction between signature absence (no signatures found) and signature mismatch (invalid signature), where candidates mistakenly think a key mismatch would cause a 'no signatures' error instead of a validation failure.

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

Cosign stores signatures as separate OCI artifacts in the same registry, using a predictable naming convention based on the image digest. The 'cosign sign' command computes the signature and pushes it as a new layer; if the push fails (e.g., due to network issues, authentication, or registry permissions), the signature is never stored. The 'cosign verify' command then queries the registry for these signature artifacts and returns 'No signatures found' if none exist. This behavior is defined by the Cosign specification (sigstore/cosign) and is independent of key validity.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the CKS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this CKS question test?

Supply Chain Security — This question tests Supply Chain Security — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The signing command failed to push the signature to the registry — The error 'No signatures found' indicates that the verification process could not locate any signature associated with the image in the registry. Since Developer B attempted to sign the image with 'cosign sign', the most likely cause is that the signing command failed to push the signature artifact (typically stored as a separate tag like 'myimage:sha256-<digest>.sig' in the same registry) to the registry. Without the signature being successfully uploaded, the 'cosign verify' command finds nothing to validate against the provided public key.

What should I do if I get this CKS question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

About these practice questions

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Same concept, more angles

1 more ways this is tested on CKS

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A CI pipeline fails with the error 'cosign: error: unable to verify image: no matching signatures' when running 'cosign verify --key pubkey.pem myregistry/myapp:latest'. The image was previously signed with a private key. What is the MOST likely cause?

hard

A.The public key is incorrect
B.The registry requires authentication
C.Cosign is not installed correctly
✓ D.The image tag was overwritten without signing

Why D: If the image tag was overwritten (e.g., pushed again without signing), the old signatures are lost and the new image is unsigned.

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