Merge pull request #1 from joshlf/stealchain-server

Add stealchain-server utility

cmd/stealchain-server/README

@@ -0,0 +1,17 @@
+stealchain-server
+
+This is a utility to extract the verified X.509 chain from a TLS
+connection initiated by another client. It listens on a port, and
+for each connection, it will dump the certificates that the peer
+actually sent (and not the verified chain that is built from this).
+
+It was written to assist in debugging issues with certificate chains.
+
+There are a few knobs:
+
+-listen specifies the address to listen on.
+
+-ca allows the trusted CA roots to be specified via a PEM bundle of
+root certificates.
+
+-verify requires that the client present a valid certificate chain.

cmd/stealchain-server/main.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/hex"
+	"encoding/pem"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+
+	"github.com/kisom/goutils/die"
+)
+
+func main() {
+	cfg := &tls.Config{}
+
+	var sysRoot, listenAddr string
+	var verify bool
+	flag.StringVar(&sysRoot, "ca", "", "provide an alternate CA bundle")
+	flag.StringVar(&listenAddr, "listen", ":443", "address to listen on")
+	flag.BoolVar(&verify, "verify", false, "verify client certificates")
+	flag.Parse()
+
+	if verify {
+		cfg.ClientAuth = tls.RequireAndVerifyClientCert
+	}
+	if sysRoot != "" {
+		pemList, err := ioutil.ReadFile(sysRoot)
+		die.If(err)
+
+		roots := x509.NewCertPool()
+		if !roots.AppendCertsFromPEM(pemList) {
+			fmt.Printf("[!] no valid roots found")
+			roots = nil
+		}
+
+		cfg.RootCAs = roots
+	}
+
+	l, err := net.Listen("tcp", listenAddr)
+	if err != nil {
+		fmt.Println(err.Error())
+		os.Exit(1)
+	}
+
+	for {
+		conn, err := l.Accept()
+		if err != nil {
+			fmt.Println(err.Error())
+		}
+
+		raddr := conn.RemoteAddr()
+		tconn := tls.Server(conn, cfg)
+		cs := tconn.ConnectionState()
+		if len(cs.PeerCertificates) == 0 {
+			fmt.Printf("[+] %v: no chain presented\n", raddr)
+			continue
+		}
+
+		var chain []byte
+		for _, cert := range cs.PeerCertificates {
+			p := &pem.Block{
+				Type:  "CERTIFICATE",
+				Bytes: cert.Raw,
+			}
+			chain = append(chain, pem.EncodeToMemory(p)...)
+		}
+
+		var nonce [16]byte
+		_, err = rand.Read(nonce[:])
+		if err != nil {
+			panic(err)
+		}
+		fname := fmt.Sprintf("%v-%v.pem", raddr, hex.EncodeToString(nonce[:]))
+		err = ioutil.WriteFile(fname, chain, 0644)
+		die.If(err)
+		fmt.Printf("%v: [+] wrote %v.\n", raddr, fname)
+	}
+}