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sig-auth: TPM-based TLS bootstrap proposal #2022

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@awly awly commented Apr 9, 2018

@k8s-ci-robot k8s-ci-robot added size/L Denotes a PR that changes 100-499 lines, ignoring generated files. cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. labels Apr 9, 2018
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[APPROVALNOTIFIER] This PR is NOT APPROVED

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@k8s-ci-robot k8s-ci-robot added needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. kind/design Categorizes issue or PR as related to design. sig/auth Categorizes an issue or PR as relevant to SIG Auth. labels Apr 9, 2018
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awly commented Apr 9, 2018

/assign @ericchiang
/cc @mikedanese

@k8s-ci-robot k8s-ci-robot requested a review from mikedanese April 9, 2018 22:26
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/assign

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Having the TPM key sign the public key in the CSR is pretty clever. Nicely prevents replays by other agents that can see the CSR.

contributors/design-proposals/auth/node-tls-bootstrap-via-tpm.md
```
csrData, err := csr.MakeNodeCSR(privateKey, nodeName)
// handle err
switch config.BootstrapCSRAttestation {
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Lots of cloud based instance identity strategies will want to inject themselves here too. I'm skeptical of adding more hard coded hooks like this into the codebase. Maybe others can weigh in here?

contributors/design-proposals/auth/node-tls-bootstrap-via-tpm.md
1. Kubelet triggers AIK creation in the TPM
1. Kubelet requests that TPM certifies (signs) ECC public key with AIK
1. Kubelet loads TPM’s AIK cert into memory
1. Kubelet builds a Certificate Signing Request (CSR) using TLS key pair
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Just to clarify. "TLS key pair" is the same as the "ECC key pair" discussed earlier and no the AIK key pair, right?

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Yep, "TLS key pair" == "ECC key pair".

contributors/design-proposals/auth/node-tls-bootstrap-via-tpm.md
Note: in this doc `privateKey` is always `crypto.PrivateKey`, not a PEM-encoded
byte blob.

### Option 2: exec authentication plugin
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This section isn't very fleshed out, but based on our conversations this requires the exec auth plugin being able to interact with opaque private keys stored on the TPM. Would it be easier and more general to add pkcs11 support to our clients for using private keys?

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In the case of exec plugin, TLS key would actually be created outside of the TPM and stored on disk. It would only be leaded in temporarily to do the signing (or "certification" in TPM lingo).
Keys created/stored in the TPM can't be exported so exec plugin wouldn't be able to pass it to kubelet.

Abstracting to PKCS11 is an interesting idea. I don't know if it would be easier from plugin author's perspective, but probably more universal. I'll think about this some more...

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@mikedanese had some thoughts on pkcs11.

Also, to clarify, this section isn't very fleshed out because exec plugin would do exactly what kubelet does currently plus changes described above. The code just happens to live in a different binary. Let me know if you'd like more detail here.

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pkcs11 is a huge spec covering way more then we need, requires dynamic loading of symbols from object files to use, and is just a painful API to work with IMO:

http://docs.oasis-open.org/pkcs11/pkcs11-curr/v2.40/cs01/pkcs11-curr-v2.40-cs01.pdf

If I wanted to write a plugin that connected a key service to the kubelet TLS stack, I would much prefer a concise, designed to purpose API (like the kms.proto), vs implementing a pkcs11 backend.

This was referenced Apr 24, 2018
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awly commented Apr 30, 2018

ping

k8s-github-robot pushed a commit to kubernetes/kubernetes that referenced this pull request May 7, 2018
Merge pull request #63266 from awly/exec-plugin-kubeconfig
c59393e 
Automatic merge from submit-queue (batch tested with PRs 63340, 63266). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

gcp: allow non-bootstrap kubeconfig

**What this PR does / why we need it**:
Needed for kubernetes/community#2022
This change lets us generate a non-bootstrap kubeconfig with exec plugin for authn.
The plugin does TLS bootstrapping internally.

**Special notes for your reviewer**:
Defaults when no new env vars are set will behave same as before this change.
`KUBELET_AUTH_TYPE` should never be `tls-auth` in practice, but leaving it there just in case.

**Release note**:
```release-note
NONE
```
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awly commented May 31, 2018

/ok-to-test

@k8s-ci-robot k8s-ci-robot removed the needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. label May 31, 2018
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Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Send feedback to sig-testing, kubernetes/test-infra and/or fejta.
/lifecycle stale

@k8s-ci-robot k8s-ci-robot added the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Aug 29, 2018
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awly commented Aug 29, 2018

This should be possible to build via exec auth plugin and some kind of (unimplemented) remote TLS handshake mechanism to abstract TPM interactions.
Abandoning this proposal.

@awly awly closed this Aug 29, 2018
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