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path: root/main.go
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package main

import (
	"bytes"
	"crypto/rsa"
	"crypto/x509"
	"encoding/hex"
	"fmt"
	"log"
	"net"
	"sync"
)

const (
	host       = `ownme.ipredator.se` // 198.167.222.202
	clientPort = `:10002`
	serverPort = `:10000`
)

type Direction int

const (
	ServerClient Direction = iota
	ClientServer
)

func (d Direction) String() string {
	switch d {
	case ServerClient:
		return "Server → Client"
	case ClientServer:
		return "Client → Server"
	}
	return "unknown"
}

type Data struct {
	Key  *rsa.PublicKey
	Rnd  []byte
	Data []byte
}

func (d Data) String() string {
	s := fmt.Sprintf("N: %v\n", d.Key.N)
	s += fmt.Sprintf("E: %v\n", d.Key.E)
	s += fmt.Sprintf("R: %x\n", d.Rnd)
	s += fmt.Sprintf("D: %x\n", d.Data)
	return s
}

var data = make(map[Direction]Data)

func (dir Direction) sniffCert(b []byte) error {
	if i := bytes.Index(b, []byte{0x30, 0x82, 0x04, 0x2f}); i >= 0 {
		cert := b[i : i+1075]
		crt, err := x509.ParseCertificate(cert)
		if err != nil {
			return err
		}
		d := data[dir]
		d.Key = crt.PublicKey.(*rsa.PublicKey)
		data[dir] = d
	}
	return nil
}

func (dir Direction) sniffRnd(b []byte) error {
	rnd := b[0x0b:0x2b]
	fmt.Println(dir, "rnd", len(rnd), "bytes")
	d := data[dir]
	d.Rnd = rnd
	data[dir] = d
	return nil
}

func (dir Direction) sniffData(b []byte) error {
	if i := bytes.Index(b, []byte{0x17, 0x03, 0x03, 0x00}); i >= 0 {
		l := int(b[4])
		d := data[dir]
		d.Data = b[i+5 : i+5+l]
		data[dir] = d
	}
	return nil
}

// Remove DHE_RSA Chifers in Client Hello
// altering any value leads to Handshake Failure after Cert Verify ???
func downgrade(b []byte) int {
	fmt.Println("downgrade")
	fmt.Println(hex.Dump(b))

	//b[0x0a] -= 2 // TLS 1.0
	b[0x04] -= 14 // handshake len
	b[0x08] -= 14 // hello len
	b[0x2d] -= 14 // cipher set len

	copy(b[0x2e:], b[0x2e+14:]) // copy second half over first (7 non dhe ciphers)
	//copy(b[0x2e+14:], b[0x2e+28:]) // preserve fist half (7 dhe ciphers)

	return len(b) - 14
}

var trydowngrade = false

func (dir Direction) sniff(src, dst net.Conn, wg *sync.WaitGroup) {
	defer wg.Done()
	buf := make([]byte, 4096) // 1452
	for k := 1; ; k++ {
		n, err := src.Read(buf)
		if err != nil {
			dst.Close()
			return
		}
		pkg := buf[:n]

		if k == 1 {
			dir.sniffRnd(pkg)
			if trydowngrade && dir == ClientServer {
				n = downgrade(pkg)
			}
		}

		fmt.Println(k, dir, n, "bytes")
		fmt.Println(hex.Dump(pkg))

		dir.sniffCert(pkg)
		dir.sniffData(pkg)

		_, err = dst.Write(pkg)
		if err != nil {
			log.Println(dir, err)
			return
		}
	}
}

func main() {
	var wg sync.WaitGroup

	srv, err := net.Dial("tcp", host+serverPort)
	if err != nil {
		log.Fatal(err)
	}
	defer srv.Close()

	cnt, err := net.Dial("tcp", host+clientPort)
	if err != nil {
		log.Fatal(err)
	}
	defer cnt.Close()

	wg.Add(2)
	go ServerClient.sniff(srv, cnt, &wg)
	go ClientServer.sniff(cnt, srv, &wg)
	wg.Wait()

	fmt.Println(ClientServer)
	fmt.Println(data[ClientServer])

	fmt.Println(ServerClient)
	fmt.Println(data[ServerClient])
}