- A
cosign sign myimage:latest --key cosign.pub
Why wrong: cosign.pub is a public key; signing requires a private key.
- B
cosign sign --key env://COSIGN_PRIVATE_KEY myimage:latest
This is the correct syntax to use a key from an environment variable.
- C
cosign sign --key $COSIGN_PRIVATE_KEY myimage:latest
Why wrong: This would use the key content as a file path, not the key itself.
- D
cosign sign --key file://cosign.key myimage:latest
Why wrong: This expects a file, not an environment variable.
Question 365 of 997
Signing Container Images with Cosign Using a Key from Environment Variable
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.
You need to sign a container image using cosign with a key stored in an environment variable. Which command should you use?
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 env://COSIGN_PRIVATE_KEY myimage:latest
Option B is correct because `cosign sign --key env://COSIGN_PRIVATE_KEY` instructs Cosign to read the private key from the environment variable named `COSIGN_PRIVATE_KEY` using the `env://` URI scheme. This is the standard way to reference a key stored in an environment variable, avoiding exposure on the command line or in files.
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 sign myimage:latest --key cosign.pub
Why it's wrong here
cosign.pub is a public key; signing requires a private key.
- ✓
cosign sign --key env://COSIGN_PRIVATE_KEY myimage:latest
Why this is correct
This is the correct syntax to use a key from an environment variable.
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 sign --key $COSIGN_PRIVATE_KEY myimage:latest
Why it's wrong here
This would use the key content as a file path, not the key itself.
- ✗
cosign sign --key file://cosign.key myimage:latest
Why it's wrong here
This expects a file, not an environment variable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The CKS exam often tests the distinction between shell variable expansion (`$VAR`) and Cosign's native `env://` URI scheme, tricking candidates into thinking that simply passing the variable value as an argument is sufficient, when in fact the `env://` prefix is required for secure key retrieval.
Detailed technical explanation
How to think about this question
Cosign supports multiple key reference URI schemes: `env://` for environment variables, `file://` for files, and `kms://` for cloud KMS providers. The `env://` scheme tells Cosign to read the key material from the named environment variable without exposing it in the process arguments, which is critical for security in CI/CD pipelines where command-line arguments may be logged. Under the hood, Cosign uses Go's `os.Getenv` to retrieve the variable value and then decodes it as a PEM-encoded private key.
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.
- →
Supply Chain Security — study guide chapter
Learn the concepts, then practise the questions
- →
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Targeted practice on this topic area only
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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 env://COSIGN_PRIVATE_KEY myimage:latest — Option B is correct because `cosign sign --key env://COSIGN_PRIVATE_KEY` instructs Cosign to read the private key from the environment variable named `COSIGN_PRIVATE_KEY` using the `env://` URI scheme. This is the standard way to reference a key stored in an environment variable, avoiding exposure on the command line or in files.
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
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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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