validator: add privatekey, derived from username

tftp/pxelinux.cfg/tpl

@@ -21,7 +21,7 @@ LABEL challenge
   MENU LABEL ^Enter Challenge
   KERNEL bzImage
   INITRD initramfs-challenge.img
-  APPEND console=tty0 quiet
+  APPEND console=tty0 adlin.login={{ .username }} adlin.key={{ .pkey }} quiet
   text help
           You are currently identified as {{ .username }}.
           Please select this menu entry in order to access the tutorial.

validator/login.go

@@ -1,6 +1,8 @@
 package main
 
 import (
+	"crypto/hmac"
+	"crypto/sha512"
 	"crypto/tls"
 	"encoding/json"
 	"errors"
@@ -17,6 +19,8 @@ import (
 	"gopkg.in/ldap.v2"
 )
 
+var loginSalt string
+
 type loginChecker struct {
 	students         []Student
 	ldapAddr         string
@@ -176,9 +180,11 @@ func (l loginChecker) lateLoginAction(username, remoteAddr string) error {
 	} else {
 		defer file.Close()
 
+		mac := hmac.New(sha512.New512_224, []byte(loginSalt))
+
 		if configTmpl, err := template.New("pxelinux.cfg").Parse(string(tpl)); err != nil {
 			log.Println("Cannot create template: ", err)
-		} else if err := configTmpl.Execute(file, map[string]string{"username": username, "remoteAddr": remoteAddr, "fname": fname}); err != nil {
+		} else if err := configTmpl.Execute(file, map[string]string{"username": username, "remoteAddr": remoteAddr, "pkey": fmt.Sprintf("%x", mac.Sum([]byte(username))), "fname": fname}); err != nil {
 			log.Println("An error occurs during template execution: ", err)
 		}
 	}

validator/main.go

@@ -18,6 +18,7 @@ func main() {
 	flag.StringVar(&studentsFile, "students", "./students.csv", "Path to a CSV file containing students list")
 	flag.StringVar(&ARPTable, "arp", ARPTable, "Path to ARP table")
 	flag.StringVar(&tftpDir, "tftpdir", "/var/tftp/", "Path to TFTPd directory")
+	flag.StringVar(&loginSalt, "loginsalt", "adelina", "secret used in login HMAC")
 
 	flag.StringVar(&lc.ldapAddr, "ldaphost", "auth.cri.epita.fr", "LDAP host")
 	flag.IntVar(&lc.ldapPort, "ldapport", 636, "LDAP port")