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# Helm Provenance and Integrity
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Helm has provenance tools which help chart users verify the integrity and origin
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of a package. Using industry-standard tools based on PKI, GnuPG, and well-respected
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package managers, Helm can generate and verify signature files.
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## Overview
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Integrity is established by comparing a chart to a provenance record. Provenance
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records are stored in _provenance files_, which are stored alongside a packaged
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chart. For example, if a chart is named `myapp-1.2.3.tgz`, its provenance file
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will be `myapp-1.2.3.tgz.prov`.
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Provenance files are generated at packaging time (`helm package --sign ...`), and
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can be checked by multiple commands, notable `helm install --verify`.
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## The Workflow
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This section describes a potential workflow for using provenance data effectively.
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Prerequisites:
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- A valid PGP keypair in a binary (not ASCII-armored) format
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- The `helm` command line tool
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- GnuPG command line tools (optional)
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- Keybase command line tools (optional)
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**NOTE:** If your PGP private key has a passphrase, you will be prompted to enter
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that passphrase for any commands that support the `--sign` option.
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Creating a new chart is the same as before:
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```
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$ helm create mychart
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Creating mychart
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```
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Once ready to package, add the `--sign` flag to `helm package`. Also, specify
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the name under which the signing key is known and the keyring containing the corresponding private key:
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```
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$ helm package --sign --key 'helm signing key' --keyring path/to/keyring.secret mychart
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```
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**TIP:** for GnuPG users, your secret keyring is in `~/.gnupg/secring.gpg`. You can
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use `gpg --list-secret-keys` to list the keys you have.
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**Warning:** the GnuPG v2 store your secret keyring using a new format 'kbx' on the default location '~/.gnupg/pubring.kbx'. Please use the following command to convert your keyring to the legacy gpg format:
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```
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$ gpg --export-secret-keys >~/.gnupg/secring.gpg
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```
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At this point, you should see both `mychart-0.1.0.tgz` and `mychart-0.1.0.tgz.prov`.
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Both files should eventually be uploaded to your desired chart repository.
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You can verify a chart using `helm verify`:
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```
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$ helm verify mychart-0.1.0.tgz
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```
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A failed verification looks like this:
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```
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$ helm verify topchart-0.1.0.tgz
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Error: sha256 sum does not match for topchart-0.1.0.tgz: "sha256:1939fbf7c1023d2f6b865d137bbb600e0c42061c3235528b1e8c82f4450c12a7" != "sha256:5a391a90de56778dd3274e47d789a2c84e0e106e1a37ef8cfa51fd60ac9e623a"
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```
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To verify during an install, use the `--verify` flag.
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```
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$ helm install --verify mychart-0.1.0.tgz
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```
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If the keyring (containing the public key associated with the signed chart) is not in the default location, you may need to point to the
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keyring with `--keyring PATH` as in the `helm package` example.
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If verification fails, the install will be aborted before the chart is even rendered.
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### Using Keybase.io credentials
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The [Keybase.io](https://keybase.io) service makes it easy to establish a chain of
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trust for a cryptographic identity. Keybase credentials can be used to sign charts.
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Prerequisites:
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- A configured Keybase.io account
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- GnuPG installed locally
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- The `keybase` CLI installed locally
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#### Signing packages
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The first step is to import your keybase keys into your local GnuPG keyring:
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```
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$ keybase pgp export -s | gpg --import
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```
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This will convert your Keybase key into the OpenPGP format, and then import it
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locally into your `~/.gnupg/secring.gpg` file.
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You can double check by running `gpg --list-secret-keys`.
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```
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$ gpg --list-secret-keys 1 ↵
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/Users/mattbutcher/.gnupg/secring.gpg
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-------------------------------------
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sec 2048R/1FC18762 2016-07-25
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uid technosophos (keybase.io/technosophos) <technosophos@keybase.io>
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ssb 2048R/D125E546 2016-07-25
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```
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Note that your secret key will have an identifier string:
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```
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technosophos (keybase.io/technosophos) <technosophos@keybase.io>
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```
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That is the full name of your key.
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Next, you can package and sign a chart with `helm package`. Make sure you use at
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least part of that name string in `--key`.
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```
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$ helm package --sign --key technosophos --keyring ~/.gnupg/secring.gpg mychart
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```
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As a result, the `package` command should produce both a `.tgz` file and a `.tgz.prov`
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file.
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#### Verifying packages
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You can also use a similar technique to verify a chart signed by someone else's
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Keybase key. Say you want to verify a package signed by `keybase.io/technosophos`.
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To do this, use the `keybase` tool:
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```
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$ keybase follow technosophos
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$ keybase pgp pull
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```
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The first command above tracks the user `technosophos`. Next `keybase pgp pull`
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downloads the OpenPGP keys of all of the accounts you follow, placing them in
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your GnuPG keyring (`~/.gnupg/pubring.gpg`).
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At this point, you can now use `helm verify` or any of the commands with a `--verify`
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flag:
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```
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$ helm verify somechart-1.2.3.tgz
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```
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### Reasons a chart may not verify
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These are common reasons for failure.
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- The prov file is missing or corrupt. This indicates that something is misconfigured
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or that the original maintainer did not create a provenance file.
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- The key used to sign the file is not in your keyring. This indicate that the
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entity who signed the chart is not someone you've already signaled that you trust.
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- The verification of the prov file failed. This indicates that something is wrong
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with either the chart or the provenance data.
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- The file hashes in the provenance file do not match the hash of the archive file. This
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indicates that the archive has been tampered with.
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If a verification fails, there is reason to distrust the package.
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## The Provenance File
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The provenance file contains a chart’s YAML file plus several pieces of
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verification information. Provenance files are designed to be automatically
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generated.
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The following pieces of provenance data are added:
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* The chart file (Chart.yaml) is included to give both humans and tools an easy
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view into the contents of the chart.
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* The signature (SHA256, just like Docker) of the chart package (the .tgz file)
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is included, and may be used to verify the integrity of the chart package.
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* The entire body is signed using the algorithm used by PGP (see
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[http://keybase.io] for an emerging way of making crypto signing and
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verification easy).
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The combination of this gives users the following assurances:
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* The package itself has not been tampered with (checksum package tgz).
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* The entity who released this package is known (via the GnuPG/PGP signature).
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The format of the file looks something like this:
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```
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-----BEGIN PGP SIGNED MESSAGE-----
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name: nginx
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description: The nginx web server as a replication controller and service pair.
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version: 0.5.1
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keywords:
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- https
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- http
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- web server
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- proxy
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source:
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- https://github.com/foo/bar
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home: http://nginx.com
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...
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files:
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nginx-0.5.1.tgz: “sha256:9f5270f50fc842cfcb717f817e95178f”
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-----BEGIN PGP SIGNATURE-----
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Version: GnuPG v1.4.9 (GNU/Linux)
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iEYEARECAAYFAkjilUEACgQkB01zfu119ZnHuQCdGCcg2YxF3XFscJLS4lzHlvte
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WkQAmQGHuuoLEJuKhRNo+Wy7mhE7u1YG
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=eifq
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-----END PGP SIGNATURE-----
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```
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Note that the YAML section contains two documents (separated by `...\n`). The
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first is the Chart.yaml. The second is the checksums, a map of filenames to
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SHA-256 digests (value shown is fake/truncated)
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The signature block is a standard PGP signature, which provides [tamper
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resistance](http://www.rossde.com/PGP/pgp_signatures.html).
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## Chart Repositories
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Chart repositories serve as a centralized collection of Helm charts.
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Chart repositories must make it possible to serve provenance files over HTTP via
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a specific request, and must make them available at the same URI path as the chart.
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For example, if the base URL for a package is `https://example.com/charts/mychart-1.2.3.tgz`,
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the provenance file, if it exists, MUST be accessible at `https://example.com/charts/mychart-1.2.3.tgz.prov`.
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From the end user's perspective, `helm install --verify myrepo/mychart-1.2.3`
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should result in the download of both the chart and the provenance file with no
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additional user configuration or action.
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## Establishing Authority and Authenticity
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When dealing with chain-of-trust systems, it is important to be able to
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establish the authority of a signer. Or, to put this plainly, the system
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above hinges on the fact that you trust the person who signed the chart.
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That, in turn, means you need to trust the public key of the signer.
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One of the design decisions with Kubernetes Helm has been that the Helm
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project would not insert itself into the chain of trust as a necessary
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party. We don't want to be "the certificate authority" for all chart
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signers. Instead, we strongly favor a decentralized model, which is part
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of the reason we chose OpenPGP as our foundational technology.
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So when it comes to establishing authority, we have left this
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step more-or-less undefined in Helm 2.0.0.
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However, we have some pointers and recommendations for those interested
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in using the provenance system:
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- The [Keybase](https://keybase.io) platform provides a public
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centralized repository for trust information.
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- You can use Keybase to store your keys or to get the public keys of others.
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- Keybase also has fabulous documentation available
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- While we haven't tested it, Keybase's "secure website" feature could
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be used to serve Helm charts.
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- The [official Kubernetes Charts project](https://github.com/helm/charts)
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is trying to solve this problem for the official chart repository.
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- There is a long issue there [detailing the current thoughts](https://github.com/helm/charts/issues/23).
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- The basic idea is that an official "chart reviewer" signs charts with
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her or his key, and the resulting provenance file is then uploaded
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to the chart repository.
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- There has been some work on the idea that a list of valid signing
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keys may be included in the `index.yaml` file of a repository.
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Finally, chain-of-trust is an evolving feature of Helm, and some
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community members have proposed adapting part of the OSI model for
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signatures. This is an open line of inquiry in the Helm team. If you're
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interested, jump on in.
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