Add info about cosign

Signed-off-by: Itxaka <[email protected]>

content/en/docs/Creating derivatives/creating_bootable_images.md

@@ -25,6 +25,7 @@ The image needs to ship:
 - grub (required)
 - dracut (optional, kernel and initrd can be consumed from the cOS repositories)
 - microcode (optional, not required in order to boot, but recomended)
+- [cosign and luet-cosign](../../getting-started/cosign) packages (optional, required if you want to verify the images installed by luet)
 
 ## Example
 
@@ -38,10 +39,16 @@ FROM quay.io/luet/base:$LUET_VERSION AS luet
 FROM opensuse/leap:15.3 # or Fedora, Ubuntu
 ARG ARCH=amd64
 ENV ARCH=${ARCH}
+ENV COSIGN_EXPERIMENTAL=1 # keyless verify
+ENV COSIGN_REPOSITORY=raccos/releases-green  # repo with the signatures
 RUN zypper in -y ... # apt-get, dnf...
 
+# Here we install cosign and luet-cosign so we can verify that the images installed have been signed
+RUN luet install -y toolchain/cosign toolchain/luet-cosign
+
 # That's where we install the minimal cos-toolkit meta-package (which pulls the minimal packages needed in order to boot)
-RUN luet install -y meta/cos-minimal
+# note that we are setting `--plugin luet-cosign` so luet verifies the correct signatures of the packages on install
+RUN luet install --plugin luet-cosign -y meta/cos-minimal
 
 # Other custom logic. E.g, customize statically the upgrade channel, default users, packages.
 ...
@@ -55,6 +62,14 @@ In the example above, the cos-toolkit parts that are **required** are pulled in
 {{<package package="system/cloud-config" >}} is optional, but provides `cOS` defaults setting, like default user/password and so on. If you are not installing it directly, an equivalent cloud-config has to be provided in order to properly boot and run a system, see [oem configuration](../../customizing/oem_configuration).
 {{% /alert %}}
 
+#### Using cosign in your derivative
+
+The {{<package package="toolchain/cosign" >}} and {{<package package="toolchain/luet-cosign" >}} are optional packages that would install cosign and luet-cosign in order to verify the packages installed by luet in the next step.
+
+You can use cosign to both verify that packages coming from cos-toolkit are verified and sign your own derivative artifacts
+
+For more info, check the [cosign](../../getting-started/cosign) page.
+
 ## Initrd
 The image should provide at least `grub`, `systemd`, `dracut`, a kernel and an initrd. Those are the common set of packages between derivatives. See also [package stack](../package_stack). 
 By default the initrd is expected to be symlinked to `/boot/initrd` and the kernel to `/boot/vmlinuz`, otherwise you can specify a custom path while [building an iso](../build_iso) and [by customizing grub](../../customizing/configure_grub).

content/en/docs/Getting started/cosign.md

@@ -0,0 +1,72 @@
+
+---
+title: "Cosign"
+linkTitle: "Cosign"
+weight: 2
+date: 2020-11-02
+description: >
+  How we use cosign in cos-toolkit
+---
+
+[Cosign](https://github.com/sigstore/cosign) is a project that signs and verifies containers and stores the signatures on OCI registries.
+
+You can check the cosign [github repo](https://github.com/sigstore/cosign) for more information.
+
+In cos-toolkit we sign every container that we generate as part of our publish process so the signature can be verified during package installation with luet or during deploy/upgrades from a deployed system to verify that the containers have not been altered in any way since their build.
+
+Currently cosign provides 2 methods for signing and verifying.
+
+ - private/public key
+ - keyless
+
+We use keyless signatures based on OIDC Identity tokens provided by github, so nobody has access to any private keys and can use them. (For more info about keyless signing/verification check [here](https://github.com/sigstore/cosign/blob/main/KEYLESS.md))
+
+This signature generation is provided by [luet-cosign](https://github.com/rancher-sandbox/luet-cosign) which is a luet plugin that generates the signatures on image push when building, and verifies them on package unpack when installing/upgrading/deploying.
+
+The process is completely transparent to the end user when upgrading/deploying a running system and using our published artifacts.
+
+When using luet-cosign as part of `luet install` you need to set `COSIGN_REPOSITORY=raccos/releases-green` and `COSIGN_EXPERIMENTAL=1` so it can find the proper signatures and use keyless verification
+
+
+{{% alert title="Note" %}}
+Currently setting `COSIGN_REPOSITORY` value is due to quay.io not supporting OCI artifacts. It may be removed in the future and signatures stored along the artifacts.
+{{% /alert %}}
+
+
+## Derivatives
+
+If building a derivative, you can also sign and verify you final artifacts with the use of [luet-cosign](https://github.com/rancher-sandbox/luet-cosign).
+
+As keyless is only possible to do in an CI environment (as it needs an OIDC token) you would need to set up private/public signature and verification.
+
+{{% alert title="Note" %}}
+If you are building and publishing your derivatives with luet on github, you can see an example on how we generate and push the keyless signatures ourselves on [this workflow](https://github.com/rancher-sandbox/cOS-toolkit/blob/master/.github/workflows/build-master-green-x86_64.yaml#L445)
+{{% /alert %}}
+
+
+### Verify cos-toolkit artifacts as part of derivative building
+
+If you consume cos-toolkit artifacts in your Dockerfile as part of building a derivative you can verify the signatures of the artifacts by setting:
+
+```dockerfile
+ENV COSIGN_REPOSITORY=raccos/releases-green
+ENV COSIGN_EXPERIMENTAL=1
+RUN luet install -y toolchain/cosign toolchain/luet-cosign # install dependencies for signature checking
+```
+
+And then making sure you call luet with `--plugin luet-cosign`. You can see an example of this in our [standard Dockerfile example](https://github.com/rancher-sandbox/cOS-toolkit/tree/master/examples/standard) 
+
+That would verify the artifacts coming from our repository.
+
+
+For signing resulting containers with a private/public key, please refer to the [cosign](https://github.com/sigstore/cosign) documents.
+
+For verifying with a private/public key, the only thing you need is to set the env var `COSIGN_PUBLIC_KEY_LOCATION` to point to the public key that signed and enable the luet-cosign plugin.
+
+{{% alert title="Note" %}}
+Currently there is an issue in which if there is more than one repo and one of those repos is not signed the whole install will fail due to cosign failing to verify the unsigned repo.
+
+If you are using luet with one or more unsigned repos, its not possible to use cosign to verify the chain.
+
+Please follow up in https://github.com/rancher-sandbox/luet-cosign/issues/6 for more info.
+{{% /alert %}}