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// Copyright 2024 OpenPubkey
//
// 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.
//
// SPDX-License-Identifier: Apache-2.0
package cert
import (
"crypto"
"crypto/rand"
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"encoding/json"
"encoding/pem"
"fmt"
"math/big"
"time"
"github.com/openpubkey/openpubkey/oidc"
"github.com/openpubkey/openpubkey/pktoken"
)
// CreateX509Cert generates a self-signed x509 cert from a PK token
// - OP 'sub' claim is mapped to the CN and SANs fields
// - User public key is mapped to the RawSubjectPublicKeyInfo field
// - Raw PK token is mapped to the SubjectKeyId field
func CreateX509Cert(pkToken *pktoken.PKToken, signer crypto.Signer) ([]byte, error) {
template, err := PktToX509Template(pkToken)
if err != nil {
return nil, fmt.Errorf("error creating X.509 template: %w", err)
}
// create a self-signed X.509 certificate
certDER, err := x509.CreateCertificate(rand.Reader, template, template, signer.Public(), signer)
if err != nil {
return nil, fmt.Errorf("error creating X.509 certificate: %w", err)
}
certBlock := &pem.Block{Type: "CERTIFICATE", Bytes: certDER}
return pem.EncodeToMemory(certBlock), nil
}
// PktToX509Template takes a PK Token and returns a X.509 certificate template
// with the fields of the template set to the values in the X509
func PktToX509Template(pkt *pktoken.PKToken) (*x509.Certificate, error) {
pktJson, err := json.Marshal(pkt)
if err != nil {
return nil, fmt.Errorf("error marshalling PK token to JSON: %w", err)
}
// get subject identifier from pk token
idtClaims := new(oidc.OidcClaims)
if err := json.Unmarshal(pkt.Payload, idtClaims); err != nil {
return nil, err
}
cic, err := pkt.GetCicValues()
if err != nil {
return nil, err
}
upk := cic.PublicKey()
var rawkey interface{} // This is the raw key, like *rsa.PrivateKey or *ecdsa.PrivateKey
if err := upk.Raw(&rawkey); err != nil {
return nil, err
}
// encode ephemeral public key
ecPub, err := x509.MarshalPKIXPublicKey(rawkey)
if err != nil {
return nil, fmt.Errorf("error marshalling public key: %w", err)
}
template := &x509.Certificate{
SerialNumber: big.NewInt(1),
Subject: pkix.Name{CommonName: idtClaims.Subject},
RawSubjectPublicKeyInfo: ecPub,
NotBefore: time.Now(),
NotAfter: time.Now().Add(365 * 24 * time.Hour), // valid for 1 year
KeyUsage: x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageCodeSigning},
BasicConstraintsValid: true,
DNSNames: []string{idtClaims.Subject},
IsCA: false,
ExtraExtensions: []pkix.Extension{{
// OID for OIDC Issuer extension
Id: asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 1},
Critical: false,
Value: []byte(idtClaims.Issuer),
}},
SubjectKeyId: pktJson,
}
return template, nil
}
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