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Add documentation for setting up Fulcio instance
This adds docs for each supported signing backend. Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>
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| # Setting up a local Fulcio instance | ||
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| There are two simple ways to set up Fulcio. | ||
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| The first is to use `docker-compose up`. This sets up both Fulcio and the Trillian instance | ||
| used for the certificate transparency (CT) log. See below for details on customizing the signing | ||
| backend, as the default uses an ephemeral CA that is not persisted. | ||
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| The other way is running the Fulcio binary: | ||
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| ``` | ||
| go run main.go serve --port 5555 --ca ephemeralca --ct-log-url="" | ||
| ``` | ||
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| This serves the API without a CT log, which is not recommended for production. | ||
| See [sigstore-the-local-way](https://github.com/tstromberg/sigstore-the-local-way) to | ||
| learn more about setting up Trillian. | ||
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| ## Signing backend | ||
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| Fulcio supports various modes to generate its code-signing certificates. These modes | ||
| support different signing backends that are responsible for both generating and | ||
| signing a certificate. | ||
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| Note that when using `docker-compose`, you may need to mount files under `volumes`. | ||
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| ### KMS | ||
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| The KMS signing backend uses KMS to generate a certificate signature. This requires | ||
| setting up a KMS key with a cloud provider, such as AWS, GCP, Azure or Hashicorp Vault. | ||
| You will also need to certify the public key of the signer, providing a certificate | ||
| chain. The CA can either run as an intermediate CA chaining up to an offline root CA, | ||
| or as a root CA, though the KMS signing backend is primarily meant to be used as an | ||
| intermediate CA. | ||
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| Configuration: | ||
| * `--ca=kmsca` | ||
| * `--kms-resource=gcpkms://<resource>`, also supporting `awskms://`, `azurekms://` or `hashivault://` | ||
| * `--kms-cert-chain-path=/...`, a PEM-encoded certificate chain | ||
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| ### Google Cloud Platform CA Service | ||
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| The GCP CA Service signing backend delegates creation and signing of the certificates | ||
| to a CA managed in GCP. You will need to create a DevOps-tier CA pool and one CA in the | ||
| CA pool. This can either be an intermediate or root CA. | ||
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| We currently do not support the following CA Service configurations. Please file an | ||
| issue if you need support. | ||
| * Enterprise-tier CA pools (The certificate ID is not sent in the request) | ||
| * CA pools with multiple CAs (Multiple places in the code expect only one certificate chain) | ||
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| Configuration: | ||
| * `--ca=googleca` | ||
| * `--gcp_private_ca_parent=projects/<project>/locations/<location>/caPools/<CA-pool>` | ||
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| ### On-disk file | ||
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| The on-disk file-based signing backend loads an encrypted key and certificate chain, and also | ||
| monitors for changes to either, reloading the key and chain without requiring a server reboot. | ||
| This signer supports a CA as either a root or intermediate. | ||
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| See [generate.sh](https://github.com/sigstore/fulcio/blob/f024a03d981f9f955b259ee7c126dd5c08d534b3/pkg/ca/fileca/testdata/generate.sh) | ||
| for examples of how to generate an encrypted private key using OpenSSL. | ||
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| Configuration: | ||
| * `--ca=fileca` | ||
| * `--fileca-cert=/...`, a PEM-encoded certificate chain | ||
| * `--fileca-key`, a PEM-encoded encrypted signing key (RSA, ECDSA, and ED25519 are supported) | ||
| * `--fileca-key-passwd`, the password to decrypt the signing key | ||
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| ### PKCS11 HSM | ||
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| The PKCS11 signing backend supports using an HSM to sign certificates. | ||
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| Configuration: | ||
| * `--ca=pkcs11ca` | ||
| * `--pkcs11-config-path=/...`, a path to a PKCS11 configuration. See `config/crypto11.conf` | ||
| * `--hsm-caroot-id=...` | ||
| * Optional: `--aws-hsm-root-ca-path=...`, a path to an AWS HSM resource | ||
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| ### Ephemeral - For testing only | ||
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| Ephemeral CAs create the key material in memory and destroy the key material on server | ||
| turndown. Do not use ephemeral CAs for production. | ||
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| Configuration: | ||
| * `--ca=ephemeralca` | ||
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| ## Certificate Transparency Log support | ||
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| All signing backends can be configured to write issued certificates to a transparency log. | ||
| Signed certificate timestamps (SCTs), proof of inclusion in the log, are returned in a | ||
| custom HTTP header or gRPC field. | ||
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| Only the KMS and File-based signing backends support embedded SCTs currently. Embedded | ||
| SCTs are recommended, since a client can easily verify proof of inclusion when using | ||
| the certificate for artifact verification, without needing to store the detached SCT | ||
| alongside the certificate. | ||
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| See [ctlog.md] for more information. | ||
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| ## CA Certificate requirements | ||
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| Certain signing backends, such as the KMS and file-based backends, require providing | ||
| your own CA certificate chain. An example PEM-encoded certificate chain: | ||
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| ``` | ||
| -----BEGIN CERTIFICATE----- | ||
| MIICGjCCAaGgAwIBAgIUALnViVfnU0brJasmRkHrn/UnfaQwCgYIKoZIzj0EAwMw | ||
| KjEVMBMGA1UEChMMc2lnc3RvcmUuZGV2MREwDwYDVQQDEwhzaWdzdG9yZTAeFw0y | ||
| MjA0MTMyMDA2MTVaFw0zMTEwMDUxMzU2NThaMDcxFTATBgNVBAoTDHNpZ3N0b3Jl | ||
| LmRldjEeMBwGA1UEAxMVc2lnc3RvcmUtaW50ZXJtZWRpYXRlMHYwEAYHKoZIzj0C | ||
| AQYFK4EEACIDYgAE8RVS/ysH+NOvuDZyPIZtilgUF9NlarYpAd9HP1vBBH1U5CV7 | ||
| 7LSS7s0ZiH4nE7Hv7ptS6LvvR/STk798LVgMzLlJ4HeIfF3tHSaexLcYpSASr1kS | ||
| 0N/RgBJz/9jWCiXno3sweTAOBgNVHQ8BAf8EBAMCAQYwEwYDVR0lBAwwCgYIKwYB | ||
| BQUHAwMwEgYDVR0TAQH/BAgwBgEB/wIBADAdBgNVHQ4EFgQU39Ppz1YkEZb5qNjp | ||
| KFWixi4YZD8wHwYDVR0jBBgwFoAUWMAeX5FFpWapesyQoZMi0CrFxfowCgYIKoZI | ||
| zj0EAwMDZwAwZAIwPCsQK4DYiZYDPIaDi5HFKnfxXx6ASSVmERfsynYBiX2X6SJR | ||
| nZU84/9DZdnFvvxmAjBOt6QpBlc4J/0DxvkTCqpclvziL6BCCPnjdlIB3Pu3BxsP | ||
| mygUY7Ii2zbdCdliiow= | ||
| -----END CERTIFICATE----- | ||
| -----BEGIN CERTIFICATE----- | ||
| MIIB9zCCAXygAwIBAgIUALZNAPFdxHPwjeDloDwyYChAO/4wCgYIKoZIzj0EAwMw | ||
| KjEVMBMGA1UEChMMc2lnc3RvcmUuZGV2MREwDwYDVQQDEwhzaWdzdG9yZTAeFw0y | ||
| MTEwMDcxMzU2NTlaFw0zMTEwMDUxMzU2NThaMCoxFTATBgNVBAoTDHNpZ3N0b3Jl | ||
| LmRldjERMA8GA1UEAxMIc2lnc3RvcmUwdjAQBgcqhkjOPQIBBgUrgQQAIgNiAAT7 | ||
| XeFT4rb3PQGwS4IajtLk3/OlnpgangaBclYpsYBr5i+4ynB07ceb3LP0OIOZdxex | ||
| X69c5iVuyJRQ+Hz05yi+UF3uBWAlHpiS5sh0+H2GHE7SXrk1EC5m1Tr19L9gg92j | ||
| YzBhMA4GA1UdDwEB/wQEAwIBBjAPBgNVHRMBAf8EBTADAQH/MB0GA1UdDgQWBBRY | ||
| wB5fkUWlZql6zJChkyLQKsXF+jAfBgNVHSMEGDAWgBRYwB5fkUWlZql6zJChkyLQ | ||
| KsXF+jAKBggqhkjOPQQDAwNpADBmAjEAj1nHeXZp+13NWBNa+EDsDP8G1WWg1tCM | ||
| WP/WHPqpaVo0jhsweNFZgSs0eE7wYI4qAjEA2WB9ot98sIkoF3vZYdd3/VtWB5b9 | ||
| TNMea7Ix/stJ5TfcLLeABLE4BNJOsQ4vnBHJ | ||
| -----END CERTIFICATE----- | ||
| ``` | ||
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| Save the chain to `chain.crt` and parse with | ||
| `openssl crl2pkcs7 -nocrl -certfile chain.crt | openssl pkcs7 -print_certs -text -noout`. | ||
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| For the root certificate: | ||
| * Subject with a common name and organization | ||
| * Key usages: Certificate Sign, CRL Sign | ||
| * CA basic constraints: CA:TRUE | ||
| * You can optionally limit the root with a path length to prevent additional | ||
| CA certificates from being issued beneath that root. | ||
| * Subject public key: We recommend using ECDSA-P384 (secp384r1) or higher, or RSA-4096. | ||
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| For the intermediate certificate: | ||
| * Subject with a common name and organization | ||
| * Key usages: Certificate Sign, CRL Sign | ||
| * Extended key usage: Code Signing | ||
| * Lifetime does not exceed the parent certificate | ||
| * CA basic constraints: CA:TRUE, pathlen:0 | ||
| * You can choose to add a different path length constraint, but we recommend limiting | ||
| the intermediate CA to only issue leaf certificates. | ||
| * Subject public key: We recommend using ECDSA-P384 (secp384r1) or higher, or RSA-4096. | ||
| We don't recommend mixing signing algorithms within the chain. | ||
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| ## Calling the Fulcio API | ||
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| To call Fulcio, you can either use `curl` or the gRPC client. It's easiest to use | ||
| Cosign to call the local instance of Fulcio. You can configure Cosign to call | ||
| the local instance with `--fulcio-url`, for example: | ||
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| ``` | ||
| COSIGN_EXPERIMENTAL=1 cosign sign --fulcio-url http://localhost:5555 container | ||
| ``` | ||
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| You will also need to configure Cosign with the local instance's root | ||
| certificate and CT log public key. You can do so by setting up a local | ||
| TUF repository, following | ||
| [this guide](https://blog.sigstore.dev/sigstore-bring-your-own-stuf-with-tuf-40febfd2badd) | ||
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| Alternatively, **for non-production testing only**, you can use environment | ||
| variables to configure the root certificate and public key. | ||
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| Set `SIGSTORE_ROOT_FILE` with the path to a PEM-encoded root certificate. | ||
| To get the root certificate, call `curl -o fulcio.crt.pem http://localhost:5555/api/v1/rootCert`. | ||
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| Set `SIGSTORE_CT_LOG_PUBLIC_KEY_FILE` with the path to a PEM or DER-encoded CT log public key. | ||
| If using `docker-compose`, the public key is available at `config/ctfe/pubkey.pem`. |