- A
cosign docker-sign myimage:latest
Why wrong: No such cosign subcommand.
- B
cosign verify --key cosign.pub myimage:latest
Why wrong: This verifies a signature, not signs.
- C
cosign sign --key cosign.key myimage:latest
Correct command to sign an image.
- D
cosign attach signature --key cosign.key myimage:latest
Why wrong: 'attach' is not a valid cosign command for signing.
Question 830 of 997
Cosign Sign Command
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.
Which command is used to sign a container image with Cosign and store the signature in an OCI registry?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"which command"Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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
✓
cosign sign --key cosign.key myimage:latest
Option C is correct because `cosign sign --key cosign.key myimage:latest` is the standard Cosign command to sign a container image using a private key and store the resulting signature in the OCI registry as an attached artifact (e.g., a `.sig` layer). This command generates a signature that is automatically pushed to the same registry alongside the image, enabling verification without external storage.
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.
- ✗
cosign docker-sign myimage:latest
Why it's wrong here
No such cosign subcommand.
- ✗
cosign verify --key cosign.pub myimage:latest
Why it's wrong here
This verifies a signature, not signs.
- ✓
cosign sign --key cosign.key myimage:latest
Why this is correct
Correct command to sign an image.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
cosign attach signature --key cosign.key myimage:latest
Why it's wrong here
'attach' is not a valid cosign command for signing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF-CKS often tests the distinction between signing (`cosign sign`) and verifying (`cosign verify`), and the trap here is that candidates may confuse the `attach` subcommand (used for non-signature artifacts) with the signing process, or assume a non-existent `docker-sign` subcommand is valid.
Trap categories for this question
Command / output trap
No such cosign subcommand.
Detailed technical explanation
How to think about this question
Under the hood, Cosign uses the `cosign sign` command to create a digital signature of the image manifest using a private key (e.g., ECDSA-P256), then stores the signature as a separate OCI artifact in the same registry, typically with a digest reference like `sha256-<digest>.sig`. This leverages the OCI Distribution Spec's support for referrers, allowing the signature to be discovered and verified without modifying the original image. In a real-world CI/CD pipeline, this ensures that only signed images are deployed, preventing tampering or unauthorized images from entering production.
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.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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.
- →
Supply Chain Security — study guide chapter
Learn the concepts, then practise the questions
- →
Supply Chain Security practice questions
Targeted practice on this topic area only
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All CKS questions
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- →
Certified Kubernetes Security Specialist CKS study guide
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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: cosign sign --key cosign.key myimage:latest — Option C is correct because `cosign sign --key cosign.key myimage:latest` is the standard Cosign command to sign a container image using a private key and store the resulting signature in the OCI registry as an attached artifact (e.g., a `.sig` layer). This command generates a signature that is automatically pushed to the same registry alongside the image, enabling verification without external storage.
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: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
4 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. Which kubectl command signs a container image using Cosign?
medium- A.crictl sign myimage:latest
- B.kubectl sign image myimage:latest
- ✓ C.cosign sign myimage:latest
- D.kubectl cosign sign myimage:latest
Why C: Cosign is a standalone tool for signing and verifying container images, not a kubectl subcommand. The correct command is `cosign sign myimage:latest`, which signs the image and stores the signature in an OCI-compliant registry alongside the image. This is part of the supply chain security workflow for ensuring image integrity and provenance.
Variation 2. Which command is used to sign a container image with Cosign?
easy- A.cosign attest
- ✓ B.cosign sign
- C.cosign generate
- D.cosign verify
Why B: The `cosign sign` command is used to sign container images and other artifacts, creating a digital signature that is stored alongside the image in the registry. This signature can later be verified with `cosign verify` to ensure the image's integrity and origin. The other options serve different purposes: `cosign attest` attaches an in-toto attestation, `cosign generate` creates key pairs, and `cosign verify` checks signatures.
Variation 3. Which command is used with Cosign to sign a container image?
easy- A.cosign verify <image>
- B.cosign attest <image>
- ✓ C.cosign sign <image>
- D.cosign generate <image>
Why C: The `cosign sign <image>` command is used to sign a container image by attaching a digital signature to the image manifest in the container registry. This signature, typically stored as a separate tag or in an OCI artifact, allows verification of the image's origin and integrity using the corresponding public key.
Variation 4. Which command would you use to sign a container image with Cosign?
easy- A.cosign push <image>
- B.cosign verify <image>
- C.cosign attest <image>
- ✓ D.cosign sign <image>
Why D: The `cosign sign <image>` command is used to sign a container image with Cosign, attaching a digital signature to the image manifest in the container registry. This signature can later be verified to ensure the image's integrity and origin, which is a core requirement for supply chain security in Kubernetes environments.
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Last reviewed: Jul 4, 2026
This CKS practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKS exam.
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