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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 ca
import (
"bytes"
"context"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/x509"
"crypto/x509/pkix"
"encoding/json"
"encoding/pem"
"fmt"
"math/big"
"time"
"github.com/lestrrat-go/jwx/v2/jwa"
"github.com/openpubkey/openpubkey/cert"
"github.com/openpubkey/openpubkey/client"
"github.com/openpubkey/openpubkey/pktoken"
"github.com/openpubkey/openpubkey/verifier"
)
type Ca struct {
pksk *ecdsa.PrivateKey
Alg jwa.KeyAlgorithm
// CaCertBytes []byte
RootCertPem []byte
op client.OpenIdProvider
}
func New(op client.OpenIdProvider) (*Ca, error) {
ca := Ca{
op: op,
}
alg := string(jwa.ES256)
err := ca.KeyGen(alg)
if err != nil {
return nil, err
}
return &ca, nil
}
func (a *Ca) KeyGen(alg string) error {
a.Alg = jwa.KeyAlgorithmFrom(alg)
pksk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return err
}
a.pksk = pksk
caTemplate := &x509.Certificate{
SerialNumber: big.NewInt(2019),
Subject: pkix.Name{
Organization: []string{"Openpubkey-test-ca-cert"},
Country: []string{"International"},
Province: []string{""},
Locality: []string{""},
StreetAddress: []string{"255 Test St."},
PostalCode: []string{""},
},
NotBefore: time.Now(),
NotAfter: time.Now().AddDate(10, 0, 0),
IsCA: true,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageCodeSigning},
KeyUsage: x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
BasicConstraintsValid: true,
}
caBytes, err := x509.CreateCertificate(rand.Reader, caTemplate, caTemplate, &a.pksk.PublicKey, a.pksk)
if err != nil {
return err
}
caPEM := new(bytes.Buffer)
pem.Encode(caPEM, &pem.Block{
Type: "CERTIFICATE",
Bytes: caBytes,
})
a.RootCertPem = caPEM.Bytes()
return nil
}
func (a *Ca) CheckPKToken(pktJson []byte) (*pktoken.PKToken, error) {
pkt := new(pktoken.PKToken)
if err := json.Unmarshal(pktJson, pkt); err != nil {
return nil, err
}
verifier, err := verifier.New(a.op)
if err != nil {
return nil, err
}
if err := verifier.VerifyPKToken(context.TODO(), pkt); err != nil {
return nil, fmt.Errorf("failed to verify PK token: %w", err)
}
return pkt, nil
}
func (a *Ca) PktToSignedX509(pktJson []byte) ([]byte, error) {
pkt, err := a.CheckPKToken(pktJson)
if err != nil {
return nil, err
}
pktUpk, err := ExtractRawPubkey(pkt)
if err != nil {
return nil, err
}
subTemplate, err := cert.PktToX509Template(pkt)
if err != nil {
return nil, err
}
rootCert, _ := pem.Decode(a.RootCertPem)
if rootCert == nil {
return nil, fmt.Errorf("failed to parse certificate PEM")
}
caTemplate, err := x509.ParseCertificate(rootCert.Bytes)
if err != nil {
return nil, err
}
subCertBytes, err := x509.CreateCertificate(rand.Reader, subTemplate, caTemplate, pktUpk, a.pksk)
if err != nil {
return nil, err
}
subCert, err := x509.ParseCertificate(subCertBytes)
if err != nil {
return nil, err
}
var pemSubCert bytes.Buffer
err = pem.Encode(&pemSubCert, &pem.Block{Type: "CERTIFICATE", Bytes: subCert.Raw})
if err != nil {
return nil, err
}
return pemSubCert.Bytes(), nil
}
// VerifyPktCert checks that the X509 cert is signed by the CA and that
// the PK Token in the cert matches the public key in the cert.
func (a *Ca) VerifyPktCert(issuedCertPEM []byte) error {
roots := x509.NewCertPool()
ok := roots.AppendCertsFromPEM([]byte(a.RootCertPem))
if !ok {
return fmt.Errorf("failed to parse root certificate")
}
block, _ := pem.Decode([]byte(issuedCertPEM))
if block == nil {
return fmt.Errorf("failed to parse certificate PEM")
}
cert, err := x509.ParseCertificate(block.Bytes)
if err != nil {
return fmt.Errorf("failed to parse certificate PEM: %w", err)
}
_, err = cert.Verify(x509.VerifyOptions{
Roots: roots,
Intermediates: x509.NewCertPool(),
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageCodeSigning},
})
if err != nil {
return fmt.Errorf("failed to verify certificate: %w", err)
}
pktJson := cert.SubjectKeyId
pkt := new(pktoken.PKToken)
if err := json.Unmarshal(pktJson, pkt); err != nil {
return err
}
pktUpk, err := ExtractRawPubkey(pkt)
if err != nil {
return err
}
certPublickey := cert.PublicKey.(*ecdsa.PublicKey)
if !certPublickey.Equal(pktUpk) {
return fmt.Errorf("public key in cert does not match PK Token's public key")
}
certPublicKeyBytes, err := x509.MarshalPKIXPublicKey(certPublickey)
if err := json.Unmarshal(pktJson, pkt); err != nil {
return err
}
if string(cert.RawSubjectPublicKeyInfo) != string(certPublicKeyBytes) {
return fmt.Errorf("certificate raw subject public key info does not match ephemeral public key")
}
// Verification succeeds
return nil
}
func ExtractRawPubkey(pkt *pktoken.PKToken) (interface{}, error) {
cic, err := pkt.GetCicValues()
if err != nil {
return nil, err
}
upk := cic.PublicKey()
var rawUpk interface{} // This is the raw key, like *rsa.PrivateKey or *ecdsa.PrivateKey
if err := upk.Raw(&rawUpk); err != nil {
return nil, err
}
return rawUpk, nil
}
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