Golang implements syn scanning

With the popularization of the Internet, network security problems are becoming increasingly serious. There are endless network attack methods, among which SYN scanning is a common attack method. SYN scanning is a way to check the accessibility of a target host by sending TCP SYN packets to the target host's open ports. This article will introduce how to implement SYN scanning using Golang.

1. The principle of SYN scanning

SYN scanning is based on the TCP three-way handshake process. When a host wants to connect to a certain port on another host, it will send a SYN packet to the target host to ask whether the port is open. If the target host receives this SYN packet and the port is indeed open, the target host will respond by sending a SYN/ACK packet with the ACK flag to the requesting host. Finally, the requesting host will send an ACK packet to establish the TCP connection. If the port is not open, the target host will send an RST packet to reject the connection request.

Therefore, the principle of SYN scanning is to send a SYN packet to the target host and wait for a response. If the response is a SYN/ACK packet, it indicates that the port is open; if the response is an RST packet, it indicates that the port is not open.

2. Use Golang to implement SYN scanning

Golang is a high-concurrency programming language that is very suitable for implementing network scanning tools. Next we will use Golang to implement SYN scanning.

1. Create a connection that can send and receive TCP packets

In Golang, you can use the "net" library to implement TCP connections. Here, we use the "net.DialTimeout" function to create a TCP connection and set the connection timeout.

conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", ipAddress, port), time.Duration(timeout)*time.Millisecond)

2. Send SYN packet

After creating the connection, we need to send a SYN packet. You can use "ErrSig" in the "go-socket.io/socket.io-protocol" library to generate a SYN packet.

SYN := socketio.Packet{
    Type: socketio.SYNT,
}
SYNBytes, err := SYN.Encode(socketio.BINARY)
if err != nil {
    return false, err
}

Then, we want to send the package to the target host.

_, err = conn.Write(SYNBytes)
if err != nil {
    return false, err
}

3. Read the response packet

Finally, we wait for the response packet. The response packet can be read using the "bufio.NewReader" function.

reader := bufio.NewReader(conn)
response, err := reader.ReadByte()
if err != nil {
    return false, err
}

If the response is a SYN/ACK packet, it indicates that the port is open; if the response is a RST packet, it indicates that the port is not open.

if response == socketio.SYNACKT.Value() {
    return true, nil
} else {
    return false, nil
}

3. Complete code implementation

The following is the complete code implementation using Golang to implement SYN scanning.

package main

import (
    "bufio"
    "fmt"
    "net"
    "time"

    "github.com/go-socket.io/socket.io-protocol"
)

func synScan(ipAddress string, port int, timeout int) (bool, error) {
    conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", ipAddress, port), time.Duration(timeout)*time.Millisecond)
    if err != nil {
        return false, err
    }
    defer conn.Close()

    SYN := socketio.Packet{
        Type: socketio.SYNT,
    }
    SYNBytes, err := SYN.Encode(socketio.BINARY)
    if err != nil {
        return false, err
    }

    _, err = conn.Write(SYNBytes)
    if err != nil {
        return false, err
    }

    reader := bufio.NewReader(conn)
    response, err := reader.ReadByte()
    if err != nil {
        return false, err
    }

    if response == socketio.SYNACKT.Value() {
        return true, nil
    } else {
        return false, nil
    }
}

func main() {
    // 定义扫描目标IP地址和端口范围
    ipAddress := "127.0.0.1"
    startPort := 1
    endPort := 100

    // 初始化结果
    results := make(map[int]bool)

    // 扫描每一个端口
    for port := startPort; port <= endPort; port++ {
        isOpen, err := synScan(ipAddress, port, 100)
        if err != nil {
            fmt.Println(err)
            continue
        }
        results[port] = isOpen
    }

    // 输出扫描结果
    for port, isOpen := range results {
        if isOpen {
            fmt.Printf("Port %d is open
", port)
        } else {
            fmt.Printf("Port %d is closed
", port)
        }
    }
}

4. Summary

This article introduces the method of using Golang to implement SYN scanning. Using Golang to implement SYN scanning can improve efficiency and accuracy, and make the code readable and maintainable. At the same time, developers can modify the code according to actual needs, such as using multi-threading or multi-coroutine to scan more ports, making it suitable for a wider range of application scenarios.

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