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tls.go
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tls.go
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// Copyright (C) 2014 The Syncthing Authors.
//
// This program 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.
//
// This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
package main
import (
"bufio"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/binary"
"encoding/pem"
"io"
"math/big"
mr "math/rand"
"net"
"os"
"path/filepath"
"time"
)
const (
tlsRSABits = 3072
tlsName = "syncthing"
)
func loadCert(dir string, prefix string) (tls.Certificate, error) {
cf := filepath.Join(dir, prefix+"cert.pem")
kf := filepath.Join(dir, prefix+"key.pem")
return tls.LoadX509KeyPair(cf, kf)
}
func certSeed(bs []byte) int64 {
hf := sha256.New()
hf.Write(bs)
id := hf.Sum(nil)
return int64(binary.BigEndian.Uint64(id))
}
func newCertificate(dir string, prefix string) {
l.Infoln("Generating RSA key and certificate...")
priv, err := rsa.GenerateKey(rand.Reader, tlsRSABits)
if err != nil {
l.Fatalln("generate key:", err)
}
notBefore := time.Now()
notAfter := time.Date(2049, 12, 31, 23, 59, 59, 0, time.UTC)
template := x509.Certificate{
SerialNumber: new(big.Int).SetInt64(mr.Int63()),
Subject: pkix.Name{
CommonName: tlsName,
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
BasicConstraintsValid: true,
}
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
if err != nil {
l.Fatalln("create cert:", err)
}
certOut, err := os.Create(filepath.Join(dir, prefix+"cert.pem"))
if err != nil {
l.Fatalln("save cert:", err)
}
err = pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
if err != nil {
l.Fatalln("save cert:", err)
}
err = certOut.Close()
if err != nil {
l.Fatalln("save cert:", err)
}
keyOut, err := os.OpenFile(filepath.Join(dir, prefix+"key.pem"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
l.Fatalln("save key:", err)
}
err = pem.Encode(keyOut, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
if err != nil {
l.Fatalln("save key:", err)
}
err = keyOut.Close()
if err != nil {
l.Fatalln("save key:", err)
}
}
type DowngradingListener struct {
net.Listener
TLSConfig *tls.Config
}
type WrappedConnection struct {
io.Reader
net.Conn
}
func (l *DowngradingListener) Accept() (net.Conn, error) {
conn, err := l.Listener.Accept()
if err != nil {
return nil, err
}
br := bufio.NewReader(conn)
bs, err := br.Peek(1)
if err != nil {
// We hit a read error here, but the Accept() call succeeded so we must not return an error.
// We return the connection as is and let whoever tries to use it deal with the error.
return conn, nil
}
wrapper := &WrappedConnection{br, conn}
// 0x16 is the first byte of a TLS handshake
if bs[0] == 0x16 {
return tls.Server(wrapper, l.TLSConfig), nil
}
return wrapper, nil
}
func (c *WrappedConnection) Read(b []byte) (n int, err error) {
return c.Reader.Read(b)
}