client.go

package main

import (
	"bufio"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"
	"net"
	"os"
)

func PkToString(k rsa.PublicKey) string {
	return string(
		pem.EncodeToMemory(
			&pem.Block{
				Type:  "RSA PUBLIC KEY",
				Bytes: x509.MarshalPKCS1PublicKey(&k),
			},
		),
	)
}
func read(c net.Conn) string {
	m, err := bufio.NewReader(c).ReadString('\n')
	if err != nil {
		fmt.Println(err)
	}
	return m
}
func getSecurityCode(publicKey rsa.PublicKey) string {
	hash := sha256.Sum256([]byte(string(publicKey.E) + publicKey.N.String()))
	return string(hash[:4]) + string(hash[4:])
}

// https://stackoverflow.com/questions/15334220/encode-decode-base64
func EncodeB64(message string) string {
	base64Text := make([]byte, base64.StdEncoding.EncodedLen(len(message)))
	base64.StdEncoding.Encode(base64Text, []byte(message))
	return string(base64Text)
}

func DecodeB64(message string) string {
	base64Text := make([]byte, base64.StdEncoding.DecodedLen(len(message)))
	base64.StdEncoding.Decode(base64Text, []byte(message))
	fmt.Printf("base64: %s\n", base64Text)
	return string(base64Text)
}
func initConn(c net.Conn, privateKey *rsa.PrivateKey, publicKey rsa.PublicKey, masterKey *[]byte) bool {
	reader := bufio.NewReader(os.Stdin)
	c.Write([]byte("hi server\n"))
	if read(c) != "hi client" {
		//return false
	}
	cID := read(c)
	c.Write([]byte("pk\n"))
	if read(c) != "ok" {
		//return false
	}

	c.Write([]byte(EncodeB64(PkToString(publicKey)) + "\n"))
	if read(c) != "ok" {
		//return false
	}
	fmt.Println("Create conversation? (y/n)")
	text1, _ := reader.ReadString('\n')
	if text1 == "y" {
		fmt.Println("Conversation id: " + cID)
		c.Write([]byte("wu\n"))
		if read(c) != "uc" {
			return false
		}
		fmt.Println("Receiver connected")
	} else {
		if read(c) != "to" {
			return false
		}
		fmt.Println("Conversation id: ")
		text2, _ := reader.ReadString('\n')
		c.Write([]byte(text2 + "\n"))
	}
	tpkH, err := x509.ParsePKCS1PublicKey([]byte(DecodeB64(read(c))))
	tpk := *tpkH
	if err != nil {
		return false
	}
	fmt.Println("Your security code: " + getSecurityCode(publicKey))
	fmt.Println("Receiver security code: " + getSecurityCode(tpk))
	fmt.Println("Please verify your security codes.")
	return true
}

const IP = "127.0.0.1"

func main() {
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	masterKey := make([]byte, 64)
	if err != nil {
		fmt.Println(err)
		return
	}
	publicKey := privateKey.PublicKey
	c, err := net.Dial("tcp4", IP+":8221")

	initConn(c, privateKey, publicKey, &masterKey)
}