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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"encoding/pem"
"flag"
"fmt"
"log"
"net"
"net/http"
"net/url"
"os"
"text/tabwriter"
)
func cloneCertificateTemplate(orig *x509.Certificate) *x509.Certificate {
return &x509.Certificate{
SerialNumber: orig.SerialNumber,
SignatureAlgorithm: orig.SignatureAlgorithm,
Issuer: orig.Issuer,
Subject: orig.Subject,
NotBefore: orig.NotBefore,
NotAfter: orig.NotAfter,
KeyUsage: orig.KeyUsage,
ExtKeyUsage: orig.ExtKeyUsage,
UnknownExtKeyUsage: orig.UnknownExtKeyUsage,
BasicConstraintsValid: orig.BasicConstraintsValid,
IsCA: orig.IsCA,
MaxPathLen: orig.MaxPathLen,
MaxPathLenZero: orig.MaxPathLenZero,
DNSNames: orig.DNSNames,
EmailAddresses: orig.EmailAddresses,
IPAddresses: orig.IPAddresses,
URIs: orig.URIs,
PolicyIdentifiers: orig.PolicyIdentifiers,
CRLDistributionPoints: orig.CRLDistributionPoints,
OCSPServer: orig.OCSPServer,
IssuingCertificateURL: orig.IssuingCertificateURL,
ExtraExtensions: orig.Extensions,
SubjectKeyId: orig.SubjectKeyId,
AuthorityKeyId: orig.AuthorityKeyId,
}
}
func cloneCertificate(urlStr string) (certFilename, keyFilename string) {
writer := tabwriter.NewWriter(os.Stdout, 0, 8, 0, '\t', tabwriter.AlignRight)
parsedURL, err := url.Parse(urlStr)
if err != nil {
log.Fatalf("[err] invalid url: %v", err)
}
host := parsedURL.Host
if parsedURL.Port() == "" {
host = host + ":443"
}
domain := parsedURL.Host
if h, _, err := net.SplitHostPort(parsedURL.Host); err == nil {
domain = h
}
certFilename = domain + "_clone.pem"
keyFilename = domain + "_clone.key"
conn, err := tls.Dial("tcp", host, &tls.Config{InsecureSkipVerify: true})
if err != nil {
log.Fatalf("[err] failed to connect to %s: %v", host, err)
}
defer conn.Close()
state := conn.ConnectionState()
if len(state.PeerCertificates) == 0 {
log.Fatal("[err] no certificates found on the target server")
}
origCert := state.PeerCertificates[0]
template := cloneCertificateTemplate(origCert)
rsaKey, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
log.Fatalf("[err] failed to generate rsa key: %v", err)
}
priv := rsaKey
pub := &rsaKey.PublicKey
parent := cloneCertificateTemplate(origCert)
parent.Subject = origCert.Issuer
certDER, err := x509.CreateCertificate(rand.Reader, template, parent, pub, priv)
if err != nil {
log.Fatalf("[err] failed to create fake certificate: %v", err)
}
certOut, err := os.Create(certFilename)
if err != nil {
log.Fatalf("[err] failed to open %s for writing: %v", certFilename, err)
}
defer certOut.Close()
if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: certDER}); err != nil {
log.Fatalf("[err] failed to write certificate: %v", err)
}
keyOut, err := os.Create(keyFilename)
if err != nil {
log.Fatalf("[err] failed to open %s for writing: %v", keyFilename, err)
}
defer keyOut.Close()
if err := pem.Encode(keyOut, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(rsaKey)}); err != nil {
log.Fatalf("[err] failed to write private key: %v", err)
}
fmt.Fprintln(writer, "url\tcloned cert\tprivate key")
fmt.Fprintf(writer, "%s\t%s\t%s", host, certFilename, keyFilename)
writer.Flush()
fmt.Println()
fmt.Println()
fmt.Println("[inf] start an https server to test cloned certificate with:")
fmt.Printf("$ %s -cert %s -key %s -port 8000\n", os.Args[0], certFilename, keyFilename)
fmt.Println()
fmt.Println("[inf] manually inspect and diff the original certificate and cloned certificate with:")
fmt.Printf("$ openssl s_client -connect %s </dev/null 2>/dev/null | openssl x509 -noout -text > %s_original.txt\n", host, parsedURL.Host)
fmt.Printf("$ openssl x509 -in %s -noout -text > %s_clone.txt\n", certFilename, certFilename)
fmt.Println("$ diff *.txt")
return
}
func runHTTPSServer(certPath, keyPath string, portNumber string) {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
fmt.Fprintln(w, "Hello, world!")
})
fmt.Printf("[inf] starting https server on https://127.0.0.1:%s\n", portNumber)
err := http.ListenAndServeTLS("127.0.0.1:"+portNumber, certPath, keyPath, nil)
if err != nil {
log.Fatalf("[err] failed to start httpsserver: %v", err)
}
}
func main() {
urlFlag := flag.String("url", "", "target https url to clone certificate from (e.g. https://google.com)")
certFlag := flag.String("cert", "", "path to certificate file to use for a test https server")
keyFlag := flag.String("key", "", "path to key file to use for a test https server")
portFlag := flag.String("port", "8000", "port to use for a test https server")
flag.Parse()
if *certFlag != "" || *keyFlag != "" {
if *certFlag == "" || *keyFlag == "" {
log.Fatal("[err] both -cert and -key must be supplied to run the HTTPS server")
}
runHTTPSServer(*certFlag, *keyFlag, *portFlag)
return
}
if *urlFlag != "" {
cloneCertificate(*urlFlag)
return
}
flag.Usage()
os.Exit(1)
}
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