Desuglify a bit

common.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"errors"
 	"time"
 )
 
@@ -16,9 +15,9 @@ const (
 var (
 	CertMagic              = [4]byte{0x44, 0x4e, 0x53, 0x43}
 	ServerMagic            = [8]byte{0x72, 0x36, 0x66, 0x6e, 0x76, 0x57, 0x6a, 0x38}
-	MinDNSPacketSize       = uint(12)
-	MaxDNSPacketSize       = uint(4096)
-	InitialMinQuestionSize = uint(128)
+	MinDNSPacketSize       = 12
+	MaxDNSPacketSize       = 4096
+	InitialMinQuestionSize = 128
 	TimeoutMin             = 1 * time.Second
 	TimeoutMax             = 5 * time.Second
 )
@@ -26,28 +25,3 @@ var (
 func HasTCFlag(packet []byte) bool {
 	return packet[2]&2 == 2
 }
-
-func Pad(packet []byte, minSize uint) []byte {
-	packet = append(packet, 0x80)
-	for uint(len(packet)) < minSize {
-		packet = append(packet, 0)
-	}
-	return packet
-}
-
-func Unpad(packet []byte) ([]byte, error) {
-	i := len(packet)
-	for {
-		if i == 0 {
-			return nil, errors.New("Invalid padding (short packet)")
-		}
-		i--
-		if packet[i] == 0x80 {
-			break
-		}
-		if packet[i] != 0x00 {
-			return nil, errors.New("Invalid padding (delimiter not found)")
-		}
-	}
-	return packet[:i], nil
-}

crypto.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"bytes"
+	"crypto/rand"
+	"errors"
+
+	"github.com/jedisct1/xsecretbox"
+)
+
+const (
+	NonceSize     = xsecretbox.NonceSize
+	HalfNonceSize = xsecretbox.NonceSize / 2
+	TagSize       = xsecretbox.TagSize
+)
+
+func pad(packet []byte, minSize int) []byte {
+	packet = append(packet, 0x80)
+	for len(packet) < minSize {
+		packet = append(packet, 0)
+	}
+	return packet
+}
+
+func unpad(packet []byte) ([]byte, error) {
+	for i := len(packet); ; {
+		if i == 0 {
+			return nil, errors.New("Invalid padding (short packet)")
+		}
+		i--
+		if packet[i] == 0x80 {
+			return packet[:i], nil
+		} else if packet[i] != 0x00 {
+			return nil, errors.New("Invalid padding (delimiter not found)")
+		}
+	}
+}
+func (proxy *Proxy) Crypt(serverInfo *ServerInfo, packet []byte) (encrypted []byte, clientNonce []byte) {
+	nonce, clientNonce := make([]byte, NonceSize), make([]byte, HalfNonceSize)
+	rand.Read(clientNonce)
+	copy(nonce, clientNonce)
+	encrypted = append(serverInfo.MagicQuery[:], proxy.proxyPublicKey[:]...)
+	encrypted = append(encrypted, nonce[:HalfNonceSize]...)
+	encrypted = xsecretbox.Seal(encrypted, nonce, pad(packet, proxy.minQuestionSize), serverInfo.SharedKey[:])
+	return
+}
+
+func (proxy *Proxy) Decrypt(serverInfo *ServerInfo, encrypted []byte, nonce []byte) ([]byte, error) {
+	serverMagicLen := len(ServerMagic)
+	responseHeaderLen := serverMagicLen + NonceSize
+	if len(encrypted) < responseHeaderLen+TagSize+int(MinDNSPacketSize) ||
+		!bytes.Equal(encrypted[:serverMagicLen], ServerMagic[:]) {
+		return encrypted, errors.New("Short message")
+	}
+	serverNonce := encrypted[serverMagicLen:responseHeaderLen]
+	if !bytes.Equal(nonce[:HalfNonceSize], serverNonce[:HalfNonceSize]) {
+		return encrypted, errors.New("Unexpected nonce")
+	}
+	packet, err := xsecretbox.Open(nil, serverNonce, encrypted[responseHeaderLen:], serverInfo.SharedKey[:])
+	if err != nil {
+		return encrypted, errors.New("Incorrect tag")
+	}
+	packet, err = unpad(packet)
+	if err != nil || len(packet) < MinDNSPacketSize {
+		return encrypted, errors.New("Incorrect padding")
+	}
+	return packet, nil
+}

dnscrypt-proxy.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"bytes"
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
@@ -10,7 +9,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/jedisct1/xsecretbox"
 	"golang.org/x/crypto/curve25519"
 	"golang.org/x/crypto/ed25519"
 )
@@ -18,7 +16,7 @@ import (
 type Proxy struct {
 	proxyPublicKey  [32]byte
 	proxySecretKey  [32]byte
-	minQuestionSize uint
+	minQuestionSize int
 	serversInfo     []ServerInfo
 }
 
@@ -88,14 +86,19 @@ type ServerInfo struct {
 	TCPAddr            *net.TCPAddr
 }
 
+func (proxy *Proxy) adjustMinQuestionSize() {
+	if MaxDNSPacketSize-proxy.minQuestionSize < proxy.minQuestionSize {
+		proxy.minQuestionSize = MaxDNSPacketSize
+	} else {
+		proxy.minQuestionSize *= 2
+	}
+}
+
 func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, packet []byte, clientAddr net.Addr, clientPc net.PacketConn) {
-	packet = Pad(packet, proxy.minQuestionSize)
-	nonce := make([]byte, xsecretbox.NonceSize)
-	rand.Read(nonce[0 : xsecretbox.NonceSize/2])
-	encrypted := serverInfo.MagicQuery[:]
-	encrypted = append(encrypted, proxy.proxyPublicKey[:]...)
-	encrypted = append(encrypted, nonce[:xsecretbox.NonceSize/2]...)
-	encrypted = xsecretbox.Seal(encrypted, nonce, packet, serverInfo.SharedKey[:])
+	if len(packet) < MinDNSPacketSize {
+		return
+	}
+	encrypted, clientNonce := proxy.Crypt(serverInfo, packet)
 	pc, err := net.DialUDP("udp", nil, serverInfo.UDPAddr)
 	if err != nil {
 		return
@@ -103,38 +106,21 @@ func (proxy *Proxy) processIncomingQuery(serverInfo *ServerInfo, packet []byte,
 	defer pc.Close()
 	pc.SetDeadline(time.Now().Add(serverInfo.Timeout))
 	pc.Write(encrypted)
-	buffer := make([]byte, MaxDNSPacketSize)
-	length, err := pc.Read(buffer)
+
+	encrypted = make([]byte, MaxDNSPacketSize)
+	length, err := pc.Read(encrypted)
 	if err != nil {
 		return
 	}
-	buffer = buffer[:length]
-	serverMagicLen := len(ServerMagic)
-	responseHeaderLen := serverMagicLen + xsecretbox.NonceSize
-	if len(buffer) < responseHeaderLen+xsecretbox.TagSize ||
-		!bytes.Equal(buffer[:serverMagicLen], ServerMagic[:]) {
-		return
-	}
-	serverNonce := buffer[serverMagicLen:responseHeaderLen]
-	if !bytes.Equal(nonce[:xsecretbox.NonceSize/2], serverNonce[:xsecretbox.NonceSize/2]) {
-		return
-	}
-	decrypted, err := xsecretbox.Open(nil, serverNonce, buffer[responseHeaderLen:], serverInfo.SharedKey[:])
+	encrypted = encrypted[:length]
+	packet, err = proxy.Decrypt(serverInfo, encrypted, clientNonce)
 	if err != nil {
 		return
 	}
-	decrypted, err = Unpad(decrypted)
-	if err != nil || uint(len(decrypted)) < MinDNSPacketSize {
-		return
+	clientPc.WriteTo(packet, clientAddr)
+	if HasTCFlag(packet) {
+		proxy.adjustMinQuestionSize()
 	}
-	if HasTCFlag(decrypted) {
-		if MaxDNSPacketSize-proxy.minQuestionSize < proxy.minQuestionSize {
-			proxy.minQuestionSize = MaxDNSPacketSize
-		} else {
-			proxy.minQuestionSize *= 2
-		}
-	}
-	clientPc.WriteTo(decrypted, clientAddr)
 }
 
 func main() {