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

labs/lab8/keys/cosign.pub

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+-----BEGIN PUBLIC KEY-----
+MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE+ANKEK9etDd23tvTC3xBnCZ8U/GV
+AeUHSNDQqh8Z5/TDSyARCP+uKdFauCQdhfnXVJ0vvpcnKkdCjx6ub7DRnA==
+-----END PUBLIC KEY-----

submissions/lab8.md

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+# Lab 8 — Submission
+
+## Task 1: Sign + Tamper Demo
+
+### Registry + image push
+- Registry container: `lab8-registry` running on `localhost:5000`
+- Image pushed: `localhost:5000/juice-shop:v20.0.0`
+- Image digest: `localhost:5000/juice-shop@sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe`
+
+### Signing
+- Output of `cosign sign` (just the success line is fine):
+```
+Signing artifact...
+Pushing signature to: localhost:5000/juice-shop
+```
+
+### Verification (PASSED)
+Output of `cosign verify` on original digest:
+```json
+[{"critical":{"identity":{"docker-reference":"localhost:5000/juice-shop@sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe"},"image":{"docker-manifest-digest":"sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe"},"type":"https://sigstore.dev/cosign/sign/v1"},"optional":{}}]
+```
+
+### Tamper Demo (FAILED — correctly)
+Output of `cosign verify` on tampered digest:
+```
+WARNING: Skipping tlog verification is an insecure practice that lacks transparency and auditability verification for the signature.
+Error: no signatures found
+error during command execution: no signatures found
+```
+
+### Sanity — original still verifies
+```
+WARNING: Skipping tlog verification is an insecure practice that lacks transparency and auditability verification for the signature.
+Verification for localhost:5000/juice-shop@sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe --
+The following checks were performed on each of these signatures:
+  - The cosign claims were validated
+  - Existence of the claims in the transparency log was verified offline
+  - The signatures were verified against the specified public key
+
+[{"critical":{"identity":{"docker-reference":"localhost:5000/juice-shop@sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe"},"image":{"docker-manifest-digest":"sha256:28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe"},"type":"https://sigstore.dev/cosign/sign/v1"},"optional":{}}]
+```
+
+### Why digest binding matters (Lecture 8 slide 6)
+The tampered tag pointed to a different digest, while the Cosign signature was bound to the original immutable digest. If Cosign signed only the mutable tag, an attacker could retag a malicious image as `v20.0.0` and inherit trust from the old tag name. Digest binding prevents that tag-mutation attack because verification follows the exact manifest hash.
+
+## Task 2: SBOM + Provenance Attestations
+
+### SBOM attestation
+- Attached: yes (`cosign attest --type cyclonedx` exit 0)
+- Verify-attestation output (first 30 lines of decoded payload):
+```json
+{
+  "_type": "https://in-toto.io/Statement/v0.1",
+  "subject": [
+    {
+      "name": "localhost:5000/juice-shop",
+      "digest": {
+        "sha256": "28870b9d2bec49e605d6ebbf4b22ed1ec1ca0a72347ef19217bbbb21ea44e3fe"
+      }
+    }
+  ],
+  "predicateType": "https://cyclonedx.org/bom",
+  "predicate": {
+    "$schema": "http://cyclonedx.org/schema/bom-1.6.schema.json",
+    "bomFormat": "CycloneDX",
+    "components": [
+      {
+        "author": "Benjamin Byholm <bbyholm@abo.fi> (https://github.com/kkoopa/), Mathias Küsel (https://github.com/mathiask88/)",
+        "bom-ref": "pkg:npm/1to2@1.0.0?package-id=3cea2309a653e6ed",
+        "cpe": "cpe:2.3:a:nodejs:1to2:1.0.0:*:*:*:*:*:*:*",
+        "description": "NAN 1 -> 2 Migration Script",
+        "externalReferences": [
+          {
+            "type": "distribution",
+            "url": "git://github.com/nodejs/nan.git"
+          }
+        ],
+        "licenses": [
+          {
+```
+- Component count matches Lab 4 source: yes
+- diff between Lab 4 SBOM and the extracted-from-attestation SBOM: `<>`
+
+### Provenance attestation
+- Attached: yes
+- Builder ID in predicate: `https://localhost/lab8-student`
+- buildType in predicate: `https://example.com/lab8/local-build`
+
+### What this gives a Lab 9 verifier (2-3 sentences)
+At K8s admission time, a Kyverno verify-images policy can require the image signature and the CycloneDX attestation before allowing deployment. A signed image without an SBOM only proves who signed the digest; it does not provide a queryable component inventory. A signed image with an SBOM lets the verifier or incident workflow answer the next Log4Shell-style question by checking whether the attested image contains the affected package.
+
+## Bonus: Blob Signing (Codecov 2021 mitigation)
+
+### Sign + verify
+- Signed: `my-tool.tar.gz` + `my-tool.tar.gz.bundle`
+- Verify-blob success output:
+```
+Verified OK
+```
+
+### Tamper test failed (correctly)
+```
+Error: failed to verify signature: could not verify message: invalid signature when validating ASN.1 encoded signature
+error during command execution: failed to verify signature: could not verify message: invalid signature when validating ASN.1 encoded signature
+```
+
+### Codecov 2021 mitigation (2-3 sentences)
+Codecov's bash uploader was distributed through `curl | bash` without verifying the downloaded bytes. If consumers had required `cosign verify-blob --key cosign.pub --bundle uploader.bundle uploader.sh` before execution, the modified uploader would not have matched the signed byte stream. The pipeline would fail before running the attacker-controlled script and before CI environment variables could be exfiltrated.