ipv4 identification randomization, changed ttl and flags when creating war ipv4 packets

Author: shadowy-pycoder

layers/ipv4.go

@@ -73,15 +73,16 @@ func NewIPv4Packet(srcIP, dstIP netip.Addr, proto IPProto, payload []byte) (*IPv
 		return nil, fmt.Errorf("malformed IPv4 address")
 	}
 	ipPacket := &IPv4Packet{
-		Version:     4,
-		IHL:         5,
-		TotalLength: uint16(headerSizeIPv4 + len(payload)),
-		Flags:       NewIPv4Flags(0),
-		TTL:         64,
-		Protocol:    &IPv4Proto{Val: proto, Desc: protodesc(proto)},
-		SrcIP:       srcIP,
-		DstIP:       dstIP,
-		Payload:     payload,
+		Version:        4,
+		IHL:            5,
+		TotalLength:    uint16(headerSizeIPv4 + len(payload)),
+		Identification: MustGenerateRandomUint16NE(),
+		Flags:          NewIPv4Flags(2),
+		TTL:            128,
+		Protocol:       &IPv4Proto{Val: proto, Desc: protodesc(proto)},
+		SrcIP:          srcIP,
+		DstIP:          dstIP,
+		Payload:        payload,
 	}
 	headerChecksum, err := CalculateIPv4Checksum(ipPacket.ToBytes())
 	if err != nil {

layers/layers.go

@@ -3,9 +3,12 @@ package layers
 
 import (
 	"bytes"
+	"crypto/rand"
 	"encoding/binary"
 	"fmt"
 	"unsafe"
+
+	"github.com/shadowy-pycoder/mshark/native"
 )
 
 const maxLenSummary = 110
@@ -273,3 +276,45 @@ func isDigit(b byte) bool {
 func isUpper(b byte) bool {
 	return b >= 'A' && b <= 'Z'
 }
+
+func GenerateRandomBytes(n int) ([]byte, error) {
+	b := make([]byte, n)
+	_, err := rand.Read(b)
+	if err != nil {
+		return nil, err
+	}
+
+	return b, nil
+}
+
+func GenerateRandomUint16LE() (uint16, error) {
+	b, err := GenerateRandomBytes(2)
+	if err != nil {
+		return 0, err
+	}
+	return binary.LittleEndian.Uint16(b), nil
+}
+
+func GenerateRandomUint16BE() (uint16, error) {
+	b, err := GenerateRandomBytes(2)
+	if err != nil {
+		return 0, err
+	}
+	return binary.BigEndian.Uint16(b), nil
+}
+
+func GenerateRandomUint16NE() (uint16, error) {
+	b, err := GenerateRandomBytes(2)
+	if err != nil {
+		return 0, err
+	}
+	return native.Endian.Uint16(b), nil
+}
+
+func MustGenerateRandomUint16NE() uint16 {
+	rn, err := GenerateRandomUint16NE()
+	if err != nil {
+		panic(err)
+	}
+	return rn
+}