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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 baseca
import (
"context"
"crypto"
"crypto/rand"
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
ct "github.com/google/certificate-transparency-go"
cttls "github.com/google/certificate-transparency-go/tls"
ctx509 "github.com/google/certificate-transparency-go/x509"
"github.com/sigstore/fulcio/pkg/ca"
"github.com/sigstore/fulcio/pkg/identity"
)
var (
// OIDExtensionCTPoison is defined in RFC 6962 s3.1.
OIDExtensionCTPoison = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 11129, 2, 4, 3}
// OIDExtensionCTSCT is defined in RFC 6962 s3.3.
OIDExtensionCTSCT = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 11129, 2, 4, 2}
)
type BaseCA struct {
// contains the chain of certificates and signer
ca.SignerWithChain
}
func (bca *BaseCA) CreatePrecertificate(ctx context.Context, principal identity.Principal, publicKey crypto.PublicKey) (*ca.CodeSigningPreCertificate, error) {
cert, err := ca.MakeX509(ctx, principal, publicKey)
if err != nil {
return nil, err
}
certChain, privateKey := bca.GetSignerWithChain()
// Append poison extension
cert.ExtraExtensions = append(cert.ExtraExtensions, pkix.Extension{
Id: OIDExtensionCTPoison,
Critical: true,
Value: asn1.NullBytes,
})
finalCertBytes, err := x509.CreateCertificate(rand.Reader, cert, certChain[0], publicKey, privateKey)
if err != nil {
return nil, err
}
csc, err := ca.CreateCSCFromDER(finalCertBytes, certChain)
if err != nil {
return nil, err
}
return &ca.CodeSigningPreCertificate{
PreCert: csc.FinalCertificate,
CertChain: csc.FinalChain,
PrivateKey: privateKey,
}, nil
}
// From https://github.com/letsencrypt/boulder/blob/54b697d51b9f63cfd6055577cd317d4096aeab08/issuance/issuance.go#L497
func generateSCTListExt(scts []ct.SignedCertificateTimestamp) (pkix.Extension, error) {
list := ctx509.SignedCertificateTimestampList{}
for _, sct := range scts {
sctBytes, err := cttls.Marshal(sct)
if err != nil {
return pkix.Extension{}, err
}
list.SCTList = append(list.SCTList, ctx509.SerializedSCT{Val: sctBytes})
}
listBytes, err := cttls.Marshal(list)
if err != nil {
return pkix.Extension{}, err
}
extBytes, err := asn1.Marshal(listBytes)
if err != nil {
return pkix.Extension{}, err
}
return pkix.Extension{
Id: OIDExtensionCTSCT,
Value: extBytes,
}, nil
}
func (bca *BaseCA) IssueFinalCertificate(_ context.Context, precert *ca.CodeSigningPreCertificate, sct *ct.SignedCertificateTimestamp) (*ca.CodeSigningCertificate, error) {
// remove poison extension from precertificate.
var exts []pkix.Extension
for _, ext := range precert.PreCert.Extensions {
if !ext.Id.Equal(OIDExtensionCTPoison) {
exts = append(exts, ext)
}
}
// append SCT extension. Supports multiple SCTs, but Fulcio only writes to one log currently.
sctExt, err := generateSCTListExt([]ct.SignedCertificateTimestamp{*sct})
if err != nil {
return nil, err
}
exts = append(exts, sctExt)
cert := precert.PreCert
cert.ExtraExtensions = exts
finalCertBytes, err := x509.CreateCertificate(rand.Reader, cert, precert.CertChain[0], precert.PreCert.PublicKey, precert.PrivateKey)
if err != nil {
return nil, err
}
return ca.CreateCSCFromDER(finalCertBytes, precert.CertChain)
}
func (bca *BaseCA) CreateCertificate(ctx context.Context, principal identity.Principal, publicKey crypto.PublicKey) (*ca.CodeSigningCertificate, error) {
cert, err := ca.MakeX509(ctx, principal, publicKey)
if err != nil {
return nil, err
}
certChain, privateKey := bca.GetSignerWithChain()
finalCertBytes, err := x509.CreateCertificate(rand.Reader, cert, certChain[0], publicKey, privateKey)
if err != nil {
return nil, err
}
return ca.CreateCSCFromDER(finalCertBytes, certChain)
}
func (bca *BaseCA) TrustBundle(_ context.Context) ([][]*x509.Certificate, error) {
certs, _ := bca.GetSignerWithChain()
return [][]*x509.Certificate{certs}, nil
}
func (bca *BaseCA) Close() error {
return nil
}
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