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Add intermediate CA implementation with KMS-backed signer
This CA implementation will use an on-disk certificate chain and a remote KMS signer to sign certificates. There is validation on server startup that the provided chain matches the provided key. I've also added a utility to generate the intermediate certificate by calling GCP CA Service. This will be used to set up Fulcio. This also refactors the code to add an intermediate CA struct that implements the common methods. This makes it simple to add new intermediate CA types, with each only needing to provide a method to fetch a signer and certificate chain. Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2022 The Sigstore Authors. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // | ||
|
|
||
| package main | ||
|
|
||
| import ( | ||
| "context" | ||
| "crypto" | ||
| "crypto/x509" | ||
| "errors" | ||
| "flag" | ||
| "log" | ||
| "os" | ||
| "time" | ||
|
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| privateca "cloud.google.com/go/security/privateca/apiv1" | ||
| "github.com/sigstore/sigstore/pkg/cryptoutils" | ||
| privatecapb "google.golang.org/genproto/googleapis/cloud/security/privateca/v1" | ||
| "google.golang.org/protobuf/types/known/durationpb" | ||
|
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| // Register the provider-specific plugins | ||
| "github.com/sigstore/sigstore/pkg/signature/kms" | ||
| _ "github.com/sigstore/sigstore/pkg/signature/kms/aws" | ||
| _ "github.com/sigstore/sigstore/pkg/signature/kms/azure" | ||
| _ "github.com/sigstore/sigstore/pkg/signature/kms/gcp" | ||
| _ "github.com/sigstore/sigstore/pkg/signature/kms/hashivault" | ||
| ) | ||
|
|
||
| /* | ||
| To run: | ||
| go run cmd/fetch_ca_cert/fetch_ca_cert.go \ | ||
| --kms-resource="gcpkms://projects/<project>/locations/<region>/keyRings/<key-ring>/cryptoKeys/<key>/versions/1" \ | ||
| --gcp-ca-parent="projects/<project>/locations/<region>/caPools/<ca-pool>" \ | ||
| --output="chain.crt.pem" | ||
| You must have the permissions to read the KMS key, and create a certificate in the CA pool. | ||
| */ | ||
|
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| var ( | ||
| gcpCaParent = flag.String("gcp-ca-parent", "", "Resource path to GCP CA Service CA") | ||
| kmsKey = flag.String("kms-resource", "", "Resource path to KMS key, starting with gcpkms://, awskms://, azurekms:// or hashivault://") | ||
| outputPath = flag.String("output", "", "Path to the output file") | ||
| ) | ||
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| func fetchCACertificate(ctx context.Context, parent, kmsKey string, client *privateca.CertificateAuthorityClient) ([]*x509.Certificate, error) { | ||
| kmsSigner, err := kms.Get(ctx, kmsKey, crypto.SHA256) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| signer, _, err := kmsSigner.CryptoSigner(ctx, func(err error) {}) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
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| pemPubKey, err := cryptoutils.MarshalPublicKeyToPEM(signer.Public()) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
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| isCa := true | ||
| // default value of 0 for int32 | ||
| var maxIssuerPathLength int32 | ||
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| csr := &privatecapb.CreateCertificateRequest{ | ||
| Parent: parent, | ||
| Certificate: &privatecapb.Certificate{ | ||
| // Default to a very large lifetime - CA Service will truncate the | ||
| // lifetime to be no longer than the root's lifetime. | ||
| // 20 years (24 hours * 365 days * 20) | ||
| Lifetime: durationpb.New(time.Hour * 24 * 365 * 20), | ||
| CertificateConfig: &privatecapb.Certificate_Config{ | ||
| Config: &privatecapb.CertificateConfig{ | ||
| PublicKey: &privatecapb.PublicKey{ | ||
| Format: privatecapb.PublicKey_PEM, | ||
| Key: pemPubKey, | ||
| }, | ||
| X509Config: &privatecapb.X509Parameters{ | ||
| KeyUsage: &privatecapb.KeyUsage{ | ||
| BaseKeyUsage: &privatecapb.KeyUsage_KeyUsageOptions{ | ||
| CertSign: true, | ||
| CrlSign: true, | ||
| }, | ||
| ExtendedKeyUsage: &privatecapb.KeyUsage_ExtendedKeyUsageOptions{ | ||
| CodeSigning: true, | ||
| }, | ||
| }, | ||
| CaOptions: &privatecapb.X509Parameters_CaOptions{ | ||
| IsCa: &isCa, | ||
| MaxIssuerPathLength: &maxIssuerPathLength, | ||
| }, | ||
| }, | ||
| SubjectConfig: &privatecapb.CertificateConfig_SubjectConfig{ | ||
| Subject: &privatecapb.Subject{ | ||
| CommonName: "sigstore-intermediate", | ||
| Organization: "sigstore.dev", | ||
| }, | ||
| }, | ||
| }, | ||
| }, | ||
| }, | ||
| } | ||
|
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| resp, err := client.CreateCertificate(ctx, csr) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| var pemCerts []string | ||
| pemCerts = append(pemCerts, resp.PemCertificate) | ||
| pemCerts = append(pemCerts, resp.PemCertificateChain...) | ||
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| var parsedCerts []*x509.Certificate | ||
| for _, c := range pemCerts { | ||
| certs, err := cryptoutils.UnmarshalCertificatesFromPEM([]byte(c)) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| if len(certs) != 1 { | ||
| return nil, errors.New("unexpected number of certificates returned") | ||
| } | ||
| parsedCerts = append(parsedCerts, certs[0]) | ||
| } | ||
|
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| return parsedCerts, nil | ||
| } | ||
|
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| func main() { | ||
| flag.Parse() | ||
|
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| if *gcpCaParent == "" { | ||
| log.Fatal("gcp-ca-parent must be set") | ||
| } | ||
| if *kmsKey == "" { | ||
| log.Fatal("kms-resource must be set") | ||
| } | ||
| if *outputPath == "" { | ||
| log.Fatal("output must be set") | ||
| } | ||
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| client, err := privateca.NewCertificateAuthorityClient(context.Background()) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| parsedCerts, err := fetchCACertificate(context.Background(), *gcpCaParent, *kmsKey, client) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| pemCerts, err := cryptoutils.MarshalCertificatesToPEM(parsedCerts) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
|
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| err = os.WriteFile(*outputPath, pemCerts, 0600) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| } |
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