update readme/usage

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
 cmd/scep/scep
+build/

README.md

@@ -1,14 +1,45 @@
-SCEP server and Go library
+`scep` is a Simple Certificate Enrollment Protocol server.
 
-# Standalone server and client binaries
-A standalone go server is available under `cmd/scep/main.go`
+# Installation
+A binary release is available on the releases page.
+
+# Usage
+
+The default flags configure and run the scep server.  
+depot must be the path to a folder with `ca.pem` and `ca.key` files. 
+
+If you don't already have a CA to use, you can create one using the `scep ca` subcommand.
 
 ```
 Usage of ./cmd/scep/scep:
+  -challenge string
+    	enforce a challenge password
   -depot string
     	path to ca folder (default "depot")
   -port string
     	port to listen on (default "8080")
+  -version
+    	prints version information
+```
+
+`scep ca -init` to create a new CA and private key. 
+
+```
+Usage of ./cmd/scep/scep ca:
+  -country string
+    	country for CA cert (default "US")
+  -depot string
+    	path to ca folder (default "depot")
+  -init
+    	create a new CA
+  -key-password string
+    	password to store rsa key
+  -keySize int
+    	rsa key size (default 4096)
+  -organization string
+    	organization for CA cert (default "scep-ca")
+  -years int
+    	default CA years (default 10)
 ```
 
 # SCEP library

cmd/scep/main.go

@@ -1,12 +1,23 @@
 package main
 
 import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
+	"encoding/pem"
+	"errors"
 	"flag"
 	"fmt"
+	"math/big"
 	"net/http"
 	"os"
 	"os/signal"
 	"syscall"
+	"time"
 
 	"github.com/go-kit/kit/log"
 	"github.com/micromdm/scep/server"
@@ -20,13 +31,30 @@ var (
 )
 
 func main() {
-	// flags
+	var caCMD = flag.NewFlagSet("ca", flag.ExitOnError)
+	{
+		if len(os.Args) >= 1 {
+			if os.Args[1] == "ca" {
+				status := caMain(caCMD)
+				os.Exit(status)
+			}
+		}
+	}
+
+	//main flags
 	var (
 		flVersion           = flag.Bool("version", false, "prints version information")
 		flPort              = flag.String("port", envString("SCEP_HTTP_LISTEN_PORT", "8080"), "port to listen on")
 		flDepotPath         = flag.String("depot", envString("SCEP_FILE_DEPOT", "depot"), "path to ca folder")
 		flChallengePassword = flag.String("challenge", envString("SCEP_CHALLENGE_PASSWORD", ""), "enforce a challenge password")
 	)
+	flag.Usage = func() {
+		flag.PrintDefaults()
+
+		fmt.Println("usage: scep [<command>] [<args>]")
+		fmt.Println(" ca <args> create/manage a CA")
+		fmt.Println("type <command> --help to see usage for each subcommand")
+	}
 	flag.Parse()
 
 	// print version information
@@ -88,6 +116,203 @@ func main() {
 	logger.Log("terminated", <-errs)
 }
 
+func caMain(cmd *flag.FlagSet) int {
+	var (
+		flDepotPath = cmd.String("depot", "depot", "path to ca folder")
+		flInit      = cmd.Bool("init", false, "create a new CA")
+		flYears     = cmd.Int("years", 10, "default CA years")
+		flKeySize   = cmd.Int("keySize", 4096, "rsa key size")
+		flOrg       = cmd.String("organization", "scep-ca", "organization for CA cert")
+		flPassword  = cmd.String("key-password", "", "password to store rsa key")
+		flCountry   = cmd.String("country", "US", "country for CA cert")
+	)
+	cmd.Parse(os.Args[2:])
+	if *flInit {
+		fmt.Println("Initializing new CA")
+		key, err := createKey(*flKeySize, []byte(*flPassword), *flDepotPath)
+		if err != nil {
+			fmt.Println(err)
+			return 1
+		}
+		if err := createCertificateAuthority(key, *flYears, *flOrg, *flCountry, *flDepotPath); err != nil {
+			fmt.Println(err)
+			return 1
+		}
+	}
+
+	return 0
+}
+
+// create a key, save it to depot and return it for further usage
+func createKey(bits int, password []byte, depot string) (*rsa.PrivateKey, error) {
+	key, err := newRSAKey(bits)
+	if err != nil {
+		return nil, err
+	}
+	e, err := encryptedKey(key, password)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := os.MkdirAll(depot, 0755); err != nil {
+		return nil, err
+	}
+
+	name := depot + "/" + "ca.key"
+	file, err := os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0400)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	if _, err := file.Write(e); err != nil {
+		file.Close()
+		os.Remove(name)
+		return nil, err
+	}
+
+	return key, nil
+}
+
+func createCertificateAuthority(key *rsa.PrivateKey, years int, organization string, country string, depot string) error {
+	var (
+		authPkixName = pkix.Name{
+			Country:            nil,
+			Organization:       nil,
+			OrganizationalUnit: []string{"SCEP CA"},
+			Locality:           nil,
+			Province:           nil,
+			StreetAddress:      nil,
+			PostalCode:         nil,
+			SerialNumber:       "",
+			CommonName:         "",
+		}
+		// Build CA based on RFC5280
+		authTemplate = x509.Certificate{
+			SerialNumber: big.NewInt(1),
+			Subject:      authPkixName,
+			// NotBefore is set to be 10min earlier to fix gap on time difference in cluster
+			NotBefore: time.Now().Add(-600).UTC(),
+			NotAfter:  time.Time{},
+			// Used for certificate signing only
+			KeyUsage: x509.KeyUsageCertSign,
+
+			ExtKeyUsage:        nil,
+			UnknownExtKeyUsage: nil,
+
+			// activate CA
+			BasicConstraintsValid: true,
+			IsCA: true,
+			// Not allow any non-self-issued intermediate CA
+			MaxPathLen: 0,
+
+			// 160-bit SHA-1 hash of the value of the BIT STRING subjectPublicKey
+			// (excluding the tag, length, and number of unused bits)
+			// **SHOULD** be filled in later
+			SubjectKeyId: nil,
+
+			// Subject Alternative Name
+			DNSNames: nil,
+
+			PermittedDNSDomainsCritical: false,
+			PermittedDNSDomains:         nil,
+		}
+	)
+
+	subjectKeyID, err := generateSubjectKeyID(&key.PublicKey)
+	if err != nil {
+		return err
+	}
+	authTemplate.SubjectKeyId = subjectKeyID
+	authTemplate.NotAfter = time.Now().AddDate(years, 0, 0).UTC()
+	authTemplate.Subject.Country = []string{country}
+	authTemplate.Subject.Organization = []string{organization}
+	crtBytes, err := x509.CreateCertificate(rand.Reader, &authTemplate, &authTemplate, &key.PublicKey, key)
+	if err != nil {
+		return err
+	}
+
+	name := depot + "/" + "ca.pem"
+	file, err := os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0400)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	if _, err := file.Write(pemCert(crtBytes)); err != nil {
+		file.Close()
+		os.Remove(name)
+		return err
+	}
+
+	return nil
+}
+
+const (
+	rsaPrivateKeyPEMBlockType = "RSA PRIVATE KEY"
+	certificatePEMBlockType   = "CERTIFICATE"
+)
+
+// rsaPublicKey reflects the ASN.1 structure of a PKCS#1 public key.
+type rsaPublicKey struct {
+	N *big.Int
+	E int
+}
+
+// GenerateSubjectKeyID generates SubjectKeyId used in Certificate
+// ID is 160-bit SHA-1 hash of the value of the BIT STRING subjectPublicKey
+func generateSubjectKeyID(pub crypto.PublicKey) ([]byte, error) {
+	var pubBytes []byte
+	var err error
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
+		pubBytes, err = asn1.Marshal(rsaPublicKey{
+			N: pub.N,
+			E: pub.E,
+		})
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, errors.New("only RSA public key is supported")
+	}
+
+	hash := sha1.Sum(pubBytes)
+
+	return hash[:], nil
+}
+
+func pemCert(derBytes []byte) []byte {
+	pemBlock := &pem.Block{
+		Type:    certificatePEMBlockType,
+		Headers: nil,
+		Bytes:   derBytes,
+	}
+	out := pem.EncodeToMemory(pemBlock)
+	return out
+}
+
+// protect an rsa key with a password
+func encryptedKey(key *rsa.PrivateKey, password []byte) ([]byte, error) {
+	privBytes := x509.MarshalPKCS1PrivateKey(key)
+	privPEMBlock, err := x509.EncryptPEMBlock(rand.Reader, rsaPrivateKeyPEMBlockType, privBytes, password, x509.PEMCipher3DES)
+	if err != nil {
+		return nil, err
+	}
+
+	out := pem.EncodeToMemory(privPEMBlock)
+	return out, nil
+}
+
+// create a new RSA private key
+func newRSAKey(bits int) (*rsa.PrivateKey, error) {
+	private, err := rsa.GenerateKey(rand.Reader, bits)
+	if err != nil {
+		return nil, err
+	}
+	return private, nil
+}
+
 func envString(key, def string) string {
 	if env := os.Getenv(key); env != "" {
 		return env

cmd/scep/release.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+VERSION="0.1.0.0"
+NAME=scep
+OUTPUT=../../build
+
+echo "Building $NAME version $VERSION"
+
+mkdir -p ${OUTPUT}
+
+build() {
+  echo -n "=> $1-$2: "
+  GOOS=$1 GOARCH=$2 go build -o ${OUTPUT}/$NAME-$1-$2 -ldflags "-X main.version=$VERSION -X main.gitHash=`git rev-parse HEAD`" ./*.go
+  du -h ${OUTPUT}/${NAME}-$1-$2
+}
+
+build "darwin" "amd64"
+build "linux" "amd64"

server/service.go

@@ -86,15 +86,16 @@ func (svc service) PKIOperation(ctx context.Context, data []byte) ([]byte, error
 	if err != nil {
 		return nil, err
 	}
+
 	// create cert template
 	tmpl := &x509.Certificate{
 		SerialNumber: serial,
 		Subject:      csr.Subject,
 		NotBefore:    time.Now().Add(-600).UTC(),
 		NotAfter:     time.Now().AddDate(1, 0, 0).UTC(),
 		SubjectKeyId: id,
+		KeyUsage:     x509.KeyUsageDigitalSignature,
 		ExtKeyUsage: []x509.ExtKeyUsage{
-			x509.ExtKeyUsageAny,
 			x509.ExtKeyUsageClientAuth,
 		},
 	}