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tls.go
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tls.go
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// Copyright (c) 2023 Proton AG
//
// This file is part of Proton Mail Bridge.
//
// Proton Mail Bridge is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Proton Mail Bridge is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
package certs
import (
"bytes"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"fmt"
"math/big"
"net"
"time"
"github.com/pkg/errors"
)
// ErrTLSCertExpiresSoon is returned when the TLS certificate is about to expire.
var ErrTLSCertExpiresSoon = fmt.Errorf("TLS certificate will expire soon")
// NewTLSTemplate creates a new TLS template certificate with a random serial number.
func NewTLSTemplate() (*x509.Certificate, error) {
serialNumber, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
if err != nil {
return nil, errors.Wrap(err, "failed to generate serial number")
}
return &x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
Country: []string{"CH"},
Organization: []string{"Proton AG"},
OrganizationalUnit: []string{"Proton Mail"},
CommonName: "127.0.0.1",
},
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
BasicConstraintsValid: true,
IsCA: true,
IPAddresses: []net.IP{net.ParseIP("127.0.0.1")},
NotBefore: time.Now(),
NotAfter: time.Now().Add(20 * 365 * 24 * time.Hour),
}, nil
}
// GenerateCert generates a new TLS certificate and returns it as PEM.
var GenerateCert = func(template *x509.Certificate) ([]byte, []byte, error) { //nolint:gochecknoglobals
priv, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
return nil, nil, errors.Wrap(err, "failed to generate private key")
}
derBytes, err := x509.CreateCertificate(rand.Reader, template, template, &priv.PublicKey, priv)
if err != nil {
return nil, nil, errors.Wrap(err, "failed to create certificate")
}
certPEM := new(bytes.Buffer)
if err := pem.Encode(certPEM, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
return nil, nil, err
}
keyPEM := new(bytes.Buffer)
if err := pem.Encode(keyPEM, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)}); err != nil {
return nil, nil, err
}
return certPEM.Bytes(), keyPEM.Bytes(), nil
}
// GetConfig tries to load TLS config or generate new one which is then returned.
func GetConfig(certPEM, keyPEM []byte) (*tls.Config, error) {
c, err := tls.X509KeyPair(certPEM, keyPEM)
if err != nil {
return nil, errors.Wrap(err, "failed to load keypair")
}
c.Leaf, err = x509.ParseCertificate(c.Certificate[0])
if err != nil {
return nil, errors.Wrap(err, "failed to parse certificate")
}
if time.Now().Add(31 * 24 * time.Hour).After(c.Leaf.NotAfter) {
return nil, ErrTLSCertExpiresSoon
}
caCertPool := x509.NewCertPool()
caCertPool.AddCert(c.Leaf)
//nolint:gosec // We need to support older TLS versions for AppleMail and Outlook
return &tls.Config{
Certificates: []tls.Certificate{c},
ServerName: "127.0.0.1",
ClientAuth: tls.VerifyClientCertIfGiven,
RootCAs: caCertPool,
ClientCAs: caCertPool,
}, nil
}