Update: thanks to peterSO the error seems to be that random bytes, read as strings will include " " which causes a newline and the error. The problem is neither
io.Copy(conn, bytes.NewReader(encrypted))
nor
conn.Write([]byte(encrypted))
work. Anyone has an idea how to write the chipertext to conn?
Original post: The chat program consists of one server and two clients. It uses TLS and NaCl for (end-to-end-)encryption. In 3/4 of cases it works, but sometimes I get an error:
panic: runtime error: slice bounds out of range
goroutine 34 [running]:
main.handleConnection(0x600a60, 0xc04246c000)
path-to/client.go:79
+0x3a6
created by main.main
path-to/client.go:44
+0x436
exit status 2
Line 44 calls
go handleConnection(conn)
Line 79 is the "decrypted" line:
func handleConnection(conn net.Conn) {
defer conn.Close()
input := bufio.NewScanner(conn)
for input.Scan() {
senderPublicKey := readKey("localPublic")
recipientPrivateKey := readKey("remotePrivate")
var decryptNonce [24]byte
encrypted := input.Bytes()
copy(decryptNonce[:], encrypted[:24])
decrypted, ok := box.Open(nil, encrypted[24:], &decryptNonce, senderPublicKey, recipientPrivateKey)
if !ok {
fmt.Println("decryption error")
}
fmt.Println(BytesToString(decrypted))
}
}
The full code is further down. As it works flawlessly without encryption and a test-implementation of just the encryption also works, I would point to the transmission between client-server-client. Normally the length of the slice shouldn't change, as the output should remain the same?
The client reads:
package main
import (
"bufio"
crypto_rand "crypto/rand"
"crypto/tls"
"crypto/x509"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"golang.org/x/crypto/nacl/box"
)
func main() {
cert, err := tls.LoadX509KeyPair("cert.pem", "key.pem")
if err != nil {
log.Fatalln("Unable to load cert", err)
}
clientCACert, err := ioutil.ReadFile("cert.pem")
if err != nil {
log.Fatal("Unable to open cert", err)
}
clientCertPool := x509.NewCertPool()
clientCertPool.AppendCertsFromPEM(clientCACert)
conf := &tls.Config{
Certificates: []tls.Certificate{cert},
RootCAs: clientCertPool,
//InsecureSkipVerify: true,
}
conn, err := tls.Dial("tcp", "localhost:443", conf)
if err != nil {
log.Fatal(err)
}
defer conn.Close()
go handleConnection(conn)
for {
stdin := bufio.NewReader(os.Stdin)
textIn, err := stdin.ReadBytes('
')
if err != nil {
fmt.Println(err)
}
var nonce [24]byte
if _, err := io.ReadFull(crypto_rand.Reader, nonce[:]); err != nil {
panic(err)
}
senderPrivateKey := readKey("localPrivate")
recipientPublicKey := readKey("remotePublic")
encrypted := box.Seal(nonce[:], textIn, &nonce, recipientPublicKey, senderPrivateKey)
text := BytesToString(encrypted)
fmt.Fprintf(conn, text+"
")
}
}
func handleConnection(conn net.Conn) {
defer conn.Close()
input := bufio.NewScanner(conn)
for input.Scan() {
senderPublicKey := readKey("localPublic")
recipientPrivateKey := readKey("remotePrivate")
var decryptNonce [24]byte
encrypted := input.Bytes()
copy(decryptNonce[:], encrypted[:24])
decrypted, ok := box.Open(nil, encrypted[24:], &decryptNonce, senderPublicKey, recipientPrivateKey)
if !ok {
fmt.Println("decryption error")
}
fmt.Println(BytesToString(decrypted))
}
}
//BytesToString converts []byte to str
func BytesToString(data []byte) string {
return string(data[:])
}
//Read the keys from file, pass filename without .ending
func readKey(name string) (prv *[32]byte) {
prv = new([32]byte)
f, err := os.Open(name + ".key")
if err != nil {
panic(err)
}
_, err = io.ReadFull(f, prv[:])
if err != nil {
panic(err)
}
return
}
The server side:
package main
import (
"bufio"
"crypto/tls"
"fmt"
"log"
"net"
)
type client chan<- string // an outgoing message channel
var (
entering = make(chan client)
leaving = make(chan client)
messages = make(chan string) // all incoming client messages
)
// Broadcast incoming message to all clients' outgoing message channels.
func broadcaster() {
clients := make(map[client]bool) // all connected clients
for {
select {
case msg := <-messages:
for cli := range clients {
cli <- msg
}
case cli := <-entering:
clients[cli] = true
case cli := <-leaving:
delete(clients, cli)
close(cli)
}
}
}
func handleConn(conn net.Conn) {
ch := make(chan string) // outgoing client messages
go clientWriter(conn, ch)
//who := conn.RemoteAddr().String()
entering <- ch
//messages <- who + " has arrived"
input := bufio.NewScanner(conn)
for input.Scan() {
messages <- input.Text()
}
//messages <- who + " has left"
leaving <- ch
conn.Close()
}
func clientWriter(conn net.Conn, ch <-chan string) {
for msg := range ch {
fmt.Fprintln(conn, msg)
}
}
func main() {
cer, err := tls.LoadX509KeyPair("cert.pem", "key.pem")
if err != nil {
log.Println(err)
return
}
config := &tls.Config{
Certificates: []tls.Certificate{cer},
//PFS, this will reject client with RSA certificates
CipherSuites: []uint16{tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384},
//Force it server side
PreferServerCipherSuites: true,
//Force TLS Version
MinVersion: tls.VersionTLS12}
listener, err := tls.Listen("tcp", "localhost:443", config)
if err != nil {
log.Fatal(err)
}
go broadcaster()
for {
conn, err := listener.Accept()
if err != nil {
log.Print(err)
continue
}
go handleConn(conn)
}
}
