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mirror of https://github.com/DNSCrypt/dnscrypt-proxy.git synced 2024-12-13 22:46:44 +01:00
dnscrypt-proxy/crypto.go
2018-01-09 16:40:37 +01:00

83 lines
2.4 KiB
Go

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) Encrypt(serverInfo *ServerInfo, packet []byte, proto string) (encrypted []byte, clientNonce []byte, err error) {
nonce, clientNonce := make([]byte, NonceSize), make([]byte, HalfNonceSize)
rand.Read(clientNonce)
copy(nonce, clientNonce)
minQuestionSize := len(packet)
if proto == "udp" {
minQuestionSize = proxy.questionSizeEstimator.MinQuestionSize()
} else {
var xpad [1]byte
rand.Read(xpad[:])
minQuestionSize += int(xpad[0])
}
paddedLength := Min((minQuestionSize+63)&^63, MaxDNSUDPPacketSize-1)
if paddedLength <= 0 || len(packet) >= paddedLength {
err = errors.New("Question too large; cannot be padded")
return
}
encrypted = append(serverInfo.MagicQuery[:], proxy.proxyPublicKey[:]...)
encrypted = append(encrypted, nonce[:HalfNonceSize]...)
encrypted = xsecretbox.Seal(encrypted, nonce, pad(packet, paddedLength), 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
}