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package main
import (
"crypto/hmac"
"crypto/rand"
"errors"
"golang.org/x/crypto/blake2s"
"net"
"sync"
"time"
)
type MACStateDevice struct {
mutex sync.RWMutex
refreshed time.Time
secret [blake2s.Size]byte
keyMAC1 [blake2s.Size]byte
keyMAC2 [blake2s.Size]byte
}
type MACStatePeer struct {
mutex sync.RWMutex
cookieSet time.Time
cookie [blake2s.Size128]byte
lastMAC1 [blake2s.Size128]byte
keyMAC1 [blake2s.Size]byte
keyMAC2 [blake2s.Size]byte
}
/* Methods for verifing MAC fields
* and creating/consuming cookies replies
* (per device)
*/
func (state *MACStateDevice) Init(pk NoisePublicKey) {
state.mutex.Lock()
defer state.mutex.Unlock()
func() {
hsh, _ := blake2s.New256(nil)
hsh.Write([]byte(WGLabelMAC1))
hsh.Write(pk[:])
hsh.Sum(state.keyMAC1[:0])
}()
func() {
hsh, _ := blake2s.New256(nil)
hsh.Write([]byte(WGLabelCookie))
hsh.Write(pk[:])
hsh.Sum(state.keyMAC2[:0])
}()
state.refreshed = time.Time{}
}
func (state *MACStateDevice) CheckMAC1(msg []byte) bool {
size := len(msg)
startMac1 := size - (blake2s.Size128 * 2)
startMac2 := size - blake2s.Size128
var mac1 [blake2s.Size128]byte
func() {
mac, _ := blake2s.New128(state.keyMAC1[:])
mac.Write(msg[:startMac1])
mac.Sum(mac1[:0])
}()
return hmac.Equal(mac1[:], msg[startMac1:startMac2])
}
func (state *MACStateDevice) CheckMAC2(msg []byte, addr *net.UDPAddr) bool {
state.mutex.RLock()
defer state.mutex.RUnlock()
if time.Now().Sub(state.refreshed) > CookieRefreshTime {
return false
}
// derive cookie key
var cookie [blake2s.Size128]byte
func() {
port := [2]byte{byte(addr.Port >> 8), byte(addr.Port)}
mac, _ := blake2s.New128(state.secret[:])
mac.Write(addr.IP)
mac.Write(port[:])
mac.Sum(cookie[:0])
}()
// calculate mac of packet
start := len(msg) - blake2s.Size128
var mac2 [blake2s.Size128]byte
func() {
mac, _ := blake2s.New128(cookie[:])
mac.Write(msg[:start])
mac.Sum(mac2[:0])
}()
return hmac.Equal(mac2[:], msg[start:])
}
func (device *Device) CreateMessageCookieReply(
msg []byte, receiver uint32, addr *net.UDPAddr,
) (*MessageCookieReply, error) {
state := &device.mac
state.mutex.RLock()
// refresh cookie secret
if time.Now().Sub(state.refreshed) > CookieRefreshTime {
state.mutex.RUnlock()
state.mutex.Lock()
_, err := rand.Read(state.secret[:])
if err != nil {
state.mutex.Unlock()
return nil, err
}
state.refreshed = time.Now()
state.mutex.Unlock()
state.mutex.RLock()
}
// derive cookie key
var cookie [blake2s.Size128]byte
func() {
port := [2]byte{byte(addr.Port >> 8), byte(addr.Port)}
mac, _ := blake2s.New128(state.secret[:])
mac.Write(addr.IP)
mac.Write(port[:])
mac.Sum(cookie[:0])
}()
// encrypt cookie
size := len(msg)
startMac1 := size - (blake2s.Size128 * 2)
startMac2 := size - blake2s.Size128
mac1 := msg[startMac1:startMac2]
reply := new(MessageCookieReply)
reply.Type = MessageCookieReplyType
reply.Receiver = receiver
_, err := rand.Read(reply.Nonce[:])
if err != nil {
state.mutex.RUnlock()
return nil, err
}
XChaCha20Poly1305Encrypt(
reply.Cookie[:0],
&reply.Nonce,
cookie[:],
mac1,
&state.keyMAC2,
)
state.mutex.RUnlock()
return reply, nil
}
func (device *Device) ConsumeMessageCookieReply(msg *MessageCookieReply) bool {
if msg.Type != MessageCookieReplyType {
return false
}
// lookup peer
lookup := device.indices.Lookup(msg.Receiver)
if lookup.handshake == nil {
return false
}
// decrypt and store cookie
var cookie [blake2s.Size128]byte
state := &lookup.peer.mac
state.mutex.Lock()
defer state.mutex.Unlock()
_, err := XChaCha20Poly1305Decrypt(
cookie[:0],
&msg.Nonce,
msg.Cookie[:],
state.lastMAC1[:],
&state.keyMAC2,
)
if err != nil {
return false
}
state.cookieSet = time.Now()
state.cookie = cookie
return true
}
/* Methods for generating the MAC fields
* (per peer)
*/
func (state *MACStatePeer) Init(pk NoisePublicKey) {
state.mutex.Lock()
defer state.mutex.Unlock()
func() {
hsh, _ := blake2s.New256(nil)
hsh.Write([]byte(WGLabelMAC1))
hsh.Write(pk[:])
hsh.Sum(state.keyMAC1[:0])
}()
func() {
hsh, _ := blake2s.New256(nil)
hsh.Write([]byte(WGLabelCookie))
hsh.Write(pk[:])
hsh.Sum(state.keyMAC2[:0])
}()
state.cookieSet = time.Time{} // never
}
func (state *MACStatePeer) AddMacs(msg []byte) {
size := len(msg)
if size < blake2s.Size128*2 {
panic(errors.New("bug: message too short"))
}
startMac1 := size - (blake2s.Size128 * 2)
startMac2 := size - blake2s.Size128
mac1 := msg[startMac1 : startMac1+blake2s.Size128]
mac2 := msg[startMac2 : startMac2+blake2s.Size128]
state.mutex.Lock()
defer state.mutex.Unlock()
// set mac1
func() {
mac, _ := blake2s.New128(state.keyMAC1[:])
mac.Write(msg[:startMac1])
mac.Sum(mac1[:0])
}()
copy(state.lastMAC1[:], mac1)
// set mac2
if state.cookieSet.IsZero() {
return
}
if time.Now().Sub(state.cookieSet) > CookieRefreshTime {
state.cookieSet = time.Time{}
return
}
func() {
mac, _ := blake2s.New128(state.cookie[:])
mac.Write(msg[:startMac2])
mac.Sum(mac2[:0])
}()
}
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