Simple TLS client tester in Go

tls.go

package main

import (
	"crypto/dsa"
	"crypto/ecdsa"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"flag"
	"fmt"
	"io/ioutil"
	"net"
	"os"
	"time"
)

var (
	cert     = flag.String("cert", "", "")
	key      = flag.String("key", "", "")
	ca       = flag.String("ca", "", "")
	insecure = flag.Bool("insecure", false, "")
	host     = flag.String("host", "localhost", "")
	port     = flag.String("port", "26257", "")
)

func main() {
	flag.Parse()

	cert, err := tls.LoadX509KeyPair(*cert, *key)
	if err != nil {
		panic(err)
	}

	caCert, err := ioutil.ReadFile(*ca)
	if err != nil {
		panic(err)
	}
	caCertPool := x509.NewCertPool()
	caCertPool.AppendCertsFromPEM(caCert)

	tlsConfig := &tls.Config{
		Certificates:             []tls.Certificate{cert},
		RootCAs:                  caCertPool,
		ServerName:               *host,
		InsecureSkipVerify:       *insecure,
		PreferServerCipherSuites: true,
		// CurvePreferences:         []tls.CurveID{tls.CurveP521, tls.CurveP384, tls.CurveP256},
		// CipherSuites: []uint16{
		// 	tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
		// 	tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
		// 	tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
		// 	tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
		// 	tls.TLS_RSA_WITH_AES_256_CBC_SHA,
		// },
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
			tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
			tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_RSA_WITH_AES_256_CBC_SHA,
		},
		MinVersion: tls.VersionTLS12,
	}
	tlsConfig.BuildNameToCertificate()

	conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%s", *host, *port), 10*time.Second)
	if err != nil {
		panic(err)
	}
	conn.SetDeadline(time.Now().Add(3 * time.Second))

	tlsConn := tls.Client(conn, tlsConfig)
	err = tlsConn.Handshake()
	if err != nil {
		panic(err)
	}

	fmt.Println("OK")

	state := tlsConn.ConnectionState()
	for _, v := range state.PeerCertificates {
		asn1Bytes, err := x509.MarshalPKIXPublicKey(v.PublicKey)
		if err != nil {
			panic(err)
		}

		pub, err := x509.ParsePKIXPublicKey(asn1Bytes)
		if err != nil {
			panic(err)
		}

		switch pub := pub.(type) {
		case *rsa.PublicKey:
			fmt.Println("RSA:", pub)
		case *dsa.PublicKey:
			fmt.Println("DSA:", pub)
		case *ecdsa.PublicKey:
			fmt.Println("ECDSA:", pub)
		default:
			panic("unknown type of public key")
		}

		block := &pem.Block{
			Type:  "PUBLIC KEY",
			Bytes: asn1Bytes,
		}

		err = pem.Encode(os.Stdout, block)
		if err != nil {
			panic(err)
		}

		fmt.Println(v.Subject)
	}
	fmt.Println("Handshake complete:", state.HandshakeComplete)
	fmt.Println("Negotiated protocol is mutual:", state.NegotiatedProtocolIsMutual)

	tlsConn.Close()
}