feat(lab8): cosign sign + SBOM/provenance attestations + blob signing

[Wilikson173]

Goal

Sign the Juice Shop image with Cosign, attach SBOM + provenance attestations, and demonstrate blob signing as a mitigation for tag-mutation and unsigned-artifact supply-chain attacks (Codecov 2021 class).

Changes

• labs/lab8/keys/cosign.pub — public key used for all verify/verify-attestation/verify-blob operations
• submissions/lab8.md — full writeup: sign + tamper demo, SBOM/provenance attestations, bonus blob signing

Testing

Registry + image push
docker run -d --name lab8-registry -p 127.0.0.1:5000:5000 registry:3
docker tag bkimminich/juice-shop:v20.0.0 localhost:5000/juice-shop:v20.0.0
docker push localhost:5000/juice-shop:v20.0.0
Sign + verify original digest
cosign sign --key labs/lab8/keys/cosign.key --yes "$DIGEST"
cosign verify --key labs/lab8/keys/cosign.pub --insecure-ignore-tlog "$DIGEST"

→ Verified OK, docker-manifest-digest matches sha256:8c76bce9...

Tamper demo (alpine re-tagged as juice-shop)
cosign verify --key labs/lab8/keys/cosign.pub --insecure-ignore-tlog "$TAMPERED_DIGEST"

→ Error: no signatures found (correctly rejected)

Sanity recheck — original still verifies after tamper attempt
cosign verify --key labs/lab8/keys/cosign.pub --insecure-ignore-tlog "$DIGEST"

→ Verified OK

SBOM attestation
cosign attest --key labs/lab8/keys/cosign.key --type cyclonedx --predicate labs/lab4/juice-shop.cdx.json --yes "$DIGEST"
cosign verify-attestation --key labs/lab8/keys/cosign.pub --insecure-ignore-tlog --type cyclonedx "$DIGEST"
diff <(jq -S '.components | length' labs/lab4/juice-shop.cdx.json)
<(jq -S '.components | length' labs/lab8/results/sbom-from-attestation.json)
→ empty diff, both 3069 components
Provenance attestation
cosign attest --key labs/lab8/keys/cosign.key --type slsaprovenance --predicate /tmp/predicate-only.json --tlog-upload=false --yes "$DIGEST"
cosign verify-attestation --key labs/lab8/keys/cosign.pub --insecure-ignore-tlog --type slsaprovenance "$DIGEST"
→ verified, builder.id = https://localhost/lab8-student
Bonus: blob signing
cosign sign-blob --key labs/lab8/keys/cosign.key --yes --bundle labs/lab8/results/my-tool.tar.gz.bundle labs/lab8/results/my-tool.tar.gz
cosign verify-blob --key cosign.pub --bundle my-tool.tar.gz.bundle --insecure-ignore-tlog my-tool.tar.gz

→ Verified OK

Tamper test on blob

echo "MALICIOUS PAYLOAD" >> my-tool.tar.gz
cosign verify-blob --key cosign.pub --bundle my-tool.tar.gz.bundle --insecure-ignore-tlog my-tool.tar.gz

→ Error: invalid signature when validating ASN.1 encoded signature (correctly rejected)

Artifacts & Screenshots

• submissions/lab8.md — full task writeup with all verification outputs

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Checklist

• Title follows feat(labN): <topic> style
• No secrets or large temp files committed
• Submission file exists at submissions/lab8.md