First write-up for the new "offline attestation" functionality

Signed-off-by: Marcio Silva <[email protected]>

Author: Marcio Silva

73-offline-attestation.md

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+# enhancement-#40: TPM 2.0 Pre-Boot Event log support
+
+<!--
+This is the title of your enhancement.  Keep it short, simple, and descriptive.  A good
+title can help communicate what the enhancement is and should be considered as part of
+any review.
+-->
+
+<!--
+A table of contents is helpful for quickly jumping to sections of a enhancement and for
+highlighting any additional information provided beyond the standard enhancement
+template.
+-->
+
+<!-- toc -->
+
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [User Stories (optional)](#user-stories-optional)
+    - [Story 1](#story-1)
+    - [Story 2](#story-2)
+  - [Notes/Constraints/Caveats (optional)](#notesconstraintscaveats-optional)
+  - [Risks and Mitigations](#risks-and-mitigations)
+- [Design Details](#design-details)
+  - [Test Plan](#test-plan)
+  - [Upgrade / Downgrade Strategy](#upgrade--downgrade-strategy)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+- [Infrastructure Needed (optional)](#infrastructure-needed-optional)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
+<!--
+**ACTION REQUIRED:** In order to merge code into a release, there must be an
+issue in [keylime/enhancements] referencing this enhancement and targeting a release**.
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+For enhancements that make changes to code or processes/procedures in core
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+Signoff checklist to be completed.
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+Check these off as they are completed for the Release Team to track. These
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+- [ ] Enhancement issue in release milestone, which links to pull request in [keylime/enhancements]
+- [ ] Core members have approved the issue with the label `implementable`
+- [ ] Design details are appropriately documented
+- [ ] Test plan is in place
+- [ ] User-facing documentation has been created in [keylime/keylime-docs]
+
+<!--
+**Note:** This checklist is iterative and should be reviewed and updated every time this enhancement is being considered for a milestone.
+-->
+
+## Summary
+
+<!--
+This section is incredibly important for producing high quality user-focused
+documentation such as release notes or a development roadmap.  It should be
+possible to collect this information before implementation begins in order to
+avoid requiring implementers to split their attention between writing release
+notes and implementing the feature itself. Reviewers
+should help to ensure that the tone and content of the `Summary` section is
+useful for a wide audience.
+
+A good summary is probably at least a paragraph in length.
+-->
+
+Provide Keylime with the ability to store all the required information to
+perform a full attestation, in a persistent external time-series datastore.
+This should also include some proof that a given AIK created on a TPM by an
+`agent` was indeed tied to a given EK, a process that is done by the
+`registrar` and whose responsibility is to store it on a tamper-resistant
+metadatastore (e.g. transparency log)
+
+## Motivation
+
+<!--
+This section is for explicitly listing the motivation, goals and non-goals of
+this enhancement.  Describe why the change is important and the benefits to users.
+-->
+
+The main motivation for adding this functionality is to give auditors and other
+compliance officers the ability to answer, with a proper degree of certainty
+and trust the following question: did node N had its software stack fully
+attested at date T?  Being date "T" a point time that could be well in the
+past, we cannot rely on the accessibility (or even the existence) of the given
+node. Furthermore we cannot even rely on the accessibility (or even the
+existence) of the server-side components of the Keylime cluster (i.e.,
+`registrar` and `verifier`) and thus need to design with these boundary
+conditions in mind.  
+
+### Goals
+
+<!--
+List the specific goals of the enhancement.  What is it trying to achieve?  How will we
+know that this has succeeded?
+-->
+
+- Add functionality on the `registrar` to record (in a tamper-resistant
+  transparency log) the association between the EK and AIK (i.e.
+`tpm2_makecredential`)
+- Add functionality on the `verifier` to record (in a time-series persistent
+  datastore) all the information needed to perform attestation standlone (i.e.,
+quotes and MB/IMA logs)
+- Add a new CLI which will interface with the aforementioned persistent stores,
+  and will call the main, umodified `verifier` code in order to do post-facto
+attestation.  
+
+### Non-Goals
+
+<!--
+What is out of scope for this enhancement?  Listing non-goals helps to focus discussion
+and make progress.
+-->
+
+- The interaction between the time-series persistent datastore and
+  tamper-resistant transparency log will be done by keylime user/operator.
+Inside the core Keylime, a "plugin" architecture will be adopted (very much
+like the "policies" for Measured Boot) and the implementation details of the
+code which will interact with such stores are outside of the scope.
+
+
+## Proposal
+
+<!--
+This is where we get down to the specifics of what the proposal actually is.
+This should have enough detail that reviewers can understand exactly what
+you're proposing, but should not include things like API designs or
+implementation.  The "Design Details" section below is for the real
+nitty-gritty.
+-->
+
+- The `registrar` will be modified to, upon initial `agent` registration -
+  which includes the execution of `tpm2_makecredential` - record the EK, AIK
+into a JSON file, sign it (using the private key generated as part of the
+certificates for mTLS interaction with both `tenant` and `registrar`) and then
+make a record of it on a tamper-resistant transparency log (e.g., Rekor). In
+addition to that, it will store the JSON file, the signature, and the public
+key on the time-series persistent datastore. This should allow an external
+component/user to check, provided that there is trust on the `registrar`, that
+a particular AIK is indeed tied to a particular EK. The reason for having this
+data stored into a time-series is due to the fact that AIKs are regenereated
+every time an `agent` is restarted on Keylime.
+- The `verifier` will be modified to take the `json_response` (python
+  dictionary) from the `agent` - which will include both quotes and logs (MB
+and IMA) - `agent` data (python dictionary) from the SQL database (internal to
+Keylime) and the `agentAttestState` python object, combine it into a single
+record and store it on the time-series persistent datastore. 
+- Two pieces of information: the name of a python module to be dynamically
+  imported (which will contain code used to interact with these new proposed
+stores) and the connection paramaters (for these new proposed stores) will be
+supplied by the user as two new parameters under `[cloud_verifier]` and
+`[registrar]` section: `persistent_store_import` and
+`persistent_store_connection_data`)
+- A new CLI interface - `keylime_attest` - will contact both the transparency
+  log and the time-series datastore, get a list of AIKs proven to be associated
+with an EK, and then call the same code used by the `verifier` (i.e.,
+`cloud_verifier_common.process_quote_response`) to perform a series of point in
+time attestation on all records retrieved from the persistent datastore.
+- An additional minor change: it is expected that the `verifier` will extract
+  the "TPM clock information" (i.e, "clock", "resetCount", "restartCount",
+"safe") and make it available as part of the `json_response` 
+
+### Notes/Constraints/Caveats (optional)
+
+<!--
+What are the caveats to the proposal?
+What are some important details that didn't come across above.
+Go in to as much detail as necessary here.
+This might be a good place to talk about core concepts and how they relate.
+-->
+
+- The `keylime_attest` CLI will call the attestation code used by the
+  `verifier` without any modification, and should be up to the user to write a
+more complex policy if he choses to do so.
+
+### Risks and Mitigations
+
+<!--
+What are the risks of this proposal and how do we mitigate.  Think broadly.
+For example, consider both security and how this will impact the larger
+enhancement ecosystem.
+
+How will security be reviewed and by whom?
+-->
+
+- The key security aspect here is to convince ourselves (and others) that the
+  record generated by the `registrar` to indicate the association between EK
+and AIK is enough. Once this is done, offline attestation has basically the
+same level of security of the online attestation (which was already evaluated)
+as it uses the very same code base. 
+- While we do expect very little impact on KeyLime's scalability by adding this
+  capability, it is important to remember that we are constantly testing KL in
+a configuration with 5K nodes (with both MB and IMA simultaneously activated),
+and can provide experimental evidence to back this hypothesis.
+
+## Design Details
+
+<!--
+This section should contain enough information that the specifics of your
+change are understandable.  This may include API specs (though not always
+required) or even code snippets.  If there's any ambiguity about HOW your
+proposal will be implemented, this is the place to discuss them.
+-->
+
+- The first PR will provide the "persistent datastore" plugin capability, to be
+  called from with both `registrar` and `verifier` code. It will include a
+default, "null operation" and all the required changes into `config.py` and
+`keylime.conf`
+- A second PR will give the `verifier` the ability to extract and store "TPM
+  clock information". This might include changes on the database schema.
+- A third PR will provide a CLI utility to perform offline attestation ### Test
+  Plan
+
+<!--
+**Note:** *Not required until targeted at a release.*
+
+Consider the following in developing a test plan for this enhancement:
+- Will there be e2e and integration tests, in addition to unit tests?
+- How will it be tested in isolation vs with other components?
+
+No need to outline all of the test cases, just the general strategy.  Anything
+that would count as tricky in the implementation and anything particularly
+challenging to test should be called out.
+
+All code is expected to have adequate tests (eventually with coverage
+expectations).
+-->
+
+- The default "null operation" plugin for the persistent datastore will allow
+  the base keylime code to be continuosly tested as it is today.
+- Given that we are not mandating any kind of specific persistent store,
+  neither for the time-series datastore nor for the tamper-resistant
+transparency log, there are no plans to perform any continous testing on it.
+
+### Upgrade / Downgrade Strategy
+
+<!--
+If applicable, how will the component be upgraded and downgraded? Make sure
+this is in the test plan.
+
+Consider the following in developing an upgrade/downgrade strategy for this enhancement
+-->
+
+- This is an optional feature, and thoroughly backward compatible with current
+  Keylime deployments.
+
+## Drawbacks
+
+<!--
+Why should this enhancement _not_ be implemented?
+-->
+
+- No known drawbacks.
+
+## Alternatives
+
+<!--
+What other approaches did you consider and why did you rule them out?  These do
+not need to be as detailed as the proposal, but should include enough
+information to express the idea and why it was not acceptable.
+-->
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+- No known alternatives.
+
+## Infrastructure Needed (optional)
+
+<!--
+Use this section if you need things infrastructure related specific to your enhancement.  Examples include a
+new subproject, repos requested, github webhook, changes to CI (travis).
+-->
+
+- Some sort of external time-series datastore and tamper-resistant transparency log will be needed in order to enable this feature.