/*
 * Echos the signed message
 */
// #########################################################
// #             WARNING   WARNING   WARNING               #
// #########################################################
// #                                                       #
// # This file is intended for demonstration purposes      #
// # only.                                                 #
// #                                                       #
// # It is the SOLE responsibility of YOU, the programmer  #
// # to prevent against unauthorized access to any signing #
// # functions.                                            #
// #                                                       #
// # Organizations that do not protect against un-         #
// # authorized signing will be black-listed to prevent    #
// # software piracy.                                      #
// #                                                       #
// # -QZ Industries, LLC                                   #
// #                                                       #
// #########################################################
/* Steps:
 *     1. Convert private key to golang compatible format:
 *        openssl rsa -in private-key.pem -out private-key-updated.pem
 */
package main

import (
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha1"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"net/http"
)

var privateKey = "C:\\path\\to\\private-key-updated.pem"
var password = "S3cur3P@ssw0rd"
var listenPort = ":8080"

func main() {
	http.HandleFunc("/", handler)
	http.ListenAndServe(listenPort, nil)
}

func handler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Add("Content-Type", "text/plain")

	rsaPrivateKey, err := decodeKey(privateKey)

	if err != nil {
		displayError(w, "Error reading key", err)
		return
	}

	data := r.URL.Query().Get("request")

	if len(data) < 1 {
		displayError(w, "Request cannot be blank", err)
		return
	}

	hash := sha1.Sum([]byte(data))
	rng := rand.Reader
	signature, err := rsa.SignPKCS1v15(rng, rsaPrivateKey, crypto.SHA1, hash[:])
	if err != nil {
		displayError(w, "Error from signing: %s\n", err)
		return
	}
	fmt.Fprintf(w, base64.StdEncoding.EncodeToString(signature))
}

func displayError(w http.ResponseWriter, msg string, err error) {
	w.WriteHeader(http.StatusInternalServerError)
	fmt.Fprintf(w, "500 - Internal Server Error\n\n"+msg+"\n\nDetails:\n", err)
}

func decodeKey(path string) (*rsa.PrivateKey, error) {
	b, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, err
	}

	block, _ := pem.Decode(b)
	if x509.IsEncryptedPEMBlock(block) {
		der, err := x509.DecryptPEMBlock(block, []byte(password))
		if err != nil {
			return nil, err
		}
		return x509.ParsePKCS1PrivateKey(der)
	}

	return x509.ParsePKCS1PrivateKey(block.Bytes)
}
