protocol: certificate generator

Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>

protocol/cert.go

@@ -0,0 +1,77 @@
+//    Licensed under the Apache License, Version 2.0 (the "License");
+//    you may not use this file except in compliance with the License.
+//    You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+package protocol
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"math/big"
+	"time"
+)
+
+type DeviceCertificate struct {
+	key  *ecdsa.PrivateKey
+	cert []byte
+}
+
+func (d *DeviceCertificate) TLSCertificate() *tls.Certificate {
+	return &tls.Certificate{
+		PrivateKey:  d.key,
+		Certificate: [][]byte{d.cert},
+	}
+}
+
+// GenerateDeviceCertificate returns a device certificate
+func GenerateDeviceCertificate(entity string) (*DeviceCertificate, error) {
+	limit := big.Int{}
+	limit.Lsh(big.NewInt(1), 128)
+	serial, err := rand.Int(rand.Reader, &limit)
+	if err != nil {
+		return nil, err
+	}
+
+	priv, err := ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+
+	startTime := time.Now()
+	// 10 years from now
+	expireTime := startTime.AddDate(10, 0, 0)
+
+	template := x509.Certificate{
+		SerialNumber: serial,
+		Subject: pkix.Name{
+			CommonName:         entity,
+			Organization:       []string{"mconnect"},
+			OrganizationalUnit: []string{"mconnect"},
+		},
+		NotBefore:             startTime,
+		NotAfter:              expireTime,
+		BasicConstraintsValid: true,
+	}
+	selfSign := template
+	cert, err := x509.CreateCertificate(rand.Reader, &template, &selfSign,
+		&priv.PublicKey, priv)
+	if err != nil {
+		return nil, err
+	}
+	devcert := &DeviceCertificate{
+		key:  priv,
+		cert: cert,
+	}
+	return devcert, nil
+}