solved secure

secure.go

@@ -6,9 +6,104 @@ import (
 "fmt"
 "bufio"
 "strings"
+"bytes"
 "strconv"
+"math/bits"
 )
 
+type Op struct {
+  op byte
+  arg byte
+}
+
+func parseSpec(c []byte) ([]Op, error) {
+  r := make([]Op, 0, 5)
+  i := 0
+  for i < len(c) {
+    last := i == len(c) - 1
+    opid := c[i]
+    arg := byte(0)
+    if opid == 0 { return r, nil}
+    if opid == 2 || opid == 4 {
+      if last { return r, fmt.Errorf("missing byte in cipherspec") }
+        i += 1
+        arg = c[i]
+    }
+    op := Op{opid, arg}
+    r = append(r, op)
+    i += 1
+  }
+  return r, nil
+}
+
+func crypt(c []Op, b byte, o int, enc bool) (byte, error) {
+  i := 0
+  for i < len(c) {
+    x := i
+    if ! enc {
+      x = len(c) - i -1
+    }
+    oper := c[x]
+
+    switch oper.op {
+      case 0: return b, nil
+      case 1:
+        b = bits.Reverse8(b)
+      case 2:
+        b = b ^ oper.arg
+      case 3:
+        b = b ^ byte(o)
+      case 4:
+        if enc {
+          b = b + oper.arg
+        } else {
+          b = b - oper.arg
+        }
+      case 5:
+        if enc {
+          b = b + byte(o)
+        } else {
+          b = b - byte(o)
+        }
+      default:
+        return 0, fmt.Errorf("invalid cipherspec %d", oper.op)
+    }
+    i += 1
+  }
+  return b, nil
+}
+
+func readEncryptedLine(r *bufio.Reader, c []Op, offset int) (string, error) {
+  off := 0
+  buf := make([]byte, 0, 32)
+  for {
+    b, err := r.ReadByte()
+    if err != nil {
+      return "", fmt.Errorf("read error")
+    }
+    b, err = crypt(c, b, off+offset, false)
+    if err != nil {
+      return "", err
+    }
+    if b == 10 { break }
+    buf = append(buf, b)
+    off += 1
+  } 
+  return string(buf), nil
+}
+
+func cryptBytes(c []Op, dat []byte, offset int, encrypt bool) ([]byte, error) {
+  buf := make([]byte, 0, 32)
+  for off := range dat {
+    b, err := crypt(c, dat[off], off+offset, encrypt)
+    if err != nil {
+      return []byte(""), err
+    }
+    buf = append(buf, b)
+  }
+  return buf, nil
+}
+
 func largestOrder(msg string) string {
   orders := strings.Split(msg, ",")
   largest := 0
@@ -37,11 +132,17 @@ func NewSecureServer(port uint16) *SecureServer {
 
 type SecureSession struct{
 	con net.Conn
+  cipspec []Op
+  sent int
+  recv int
 }
 
 func NewSecureSession(con net.Conn) *SecureSession {
 	return &SecureSession{
 		con,
+    make([]Op, 0),
+    0,
+    0,
 	}
 }
 
@@ -74,21 +175,42 @@ func (s *SecureServer) processClient(con net.Conn) {
 }
 
 
-func (s *SecureSession) setEncryption(r *bufio.Reader) error {
+func (s *SecureSession) setCipher(r *bufio.Reader) error {
-	secdef, err := r.ReadBytes('\x00')
+	cipspecStr, err := r.ReadBytes('\x00')
 	if err != nil { return err }
-  fmt.Printf("secdef: %s\n", secdef)
+  fmt.Printf("cipspec: %x\n", cipspecStr)
+  cipspec, err := parseSpec(cipspecStr)
+  if err != nil { return err }
+  s.cipspec = cipspec
+  dummy := []byte("abcd")
+  result, err := cryptBytes(cipspec, dummy, 0, true)
+  if err != nil { return err }
+  if bytes.Equal(result, dummy) {
+    return fmt.Errorf("transparent cipspec")
+  }
+  decrypt, err := cryptBytes(cipspec, result, 0, false)
+  if err != nil { return err }
+  if ! bytes.Equal(dummy, decrypt) {
+    return fmt.Errorf("Sanity decrypt failed: %s", decrypt)
+  }
+  fmt.Println("Spec approved")
 	return nil
 }
 
 func (s *SecureSession) query(r *bufio.Reader) error {
-	msg, err := r.ReadString('\n')
+  fmt.Printf("Recv %d sent %d \n", s.recv, s.sent)
+	msg, err := readEncryptedLine(r, s.cipspec, s.recv)
+  s.recv += len(msg) + 1
 	if err != nil { return err }
 	msg = strings.TrimSpace(msg)
-  fmt.Printf("Q: %s", msg)
+  fmt.Printf("Q: %s\n", msg)
   a := largestOrder(msg)
   fmt.Printf("A: %s\n", a)
-  s.con.Write(append([]byte(a), []byte("\n")...))
+  resp := append([]byte(a), []byte("\n")...)
+  resp, err = cryptBytes(s.cipspec, resp, s.sent, true)
+  s.sent += len(resp)
+  if err != nil { return err }
+  s.con.Write(resp)
 	return nil
 }
 
@@ -100,9 +222,10 @@ func (s *SecureSession) close() {
 func (s *SecureSession) SecureReceiver() {
 	defer s.close()
 	r := bufio.NewReaderSize(s.con, 5000)
-	err := s.setEncryption(r)
+	err := s.setCipher(r)
 	for err == nil {
 		err = s.query(r)
 	}
+  fmt.Printf("%e\n", err)
 }
 

tests/secure.py

@@ -1,6 +1,7 @@
 import socket
 from struct import pack, unpack
 from time import time, sleep
+from binascii import unhexlify
 
 def sock():
   addr = ("localhost", 13370)
@@ -9,8 +10,10 @@ def sock():
   return s
   
 def test(s):
-  s.sendall(b"\x0010x snoeperfloep,123x sapperflap\n")
+  s.sendall(b"\x04\x01\x0010x snoeperfloep,123x sapperflap\x11")
   print(s.recv(1024))
   s.close()
 
-test(sock())
+def insane(s): s.sendall(unhexlify("03050105050500"))
+
+insane(sock())