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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"errors"
"fmt"
"io/ioutil"
"math/big"
"os"
"time"
)
const (
certificatePEMBlockType = "CERTIFICATE"
)
func pemCert(derBytes []byte) []byte {
pemBlock := &pem.Block{
Type: certificatePEMBlockType,
Headers: nil,
Bytes: derBytes,
}
out := pem.EncodeToMemory(pemBlock)
return out
}
func loadOrSign(path string, priv *rsa.PrivateKey, csr *x509.CertificateRequest) (*x509.Certificate, error) {
file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
if err != nil {
if os.IsExist(err) {
return loadPEMCertFromFile(path)
}
return nil, err
}
defer file.Close()
self, err := selfSign(priv, csr)
if err != nil {
return nil, err
}
pemBlock := &pem.Block{
Type: certificatePEMBlockType,
Headers: nil,
Bytes: self.Raw,
}
if err = pem.Encode(file, pemBlock); err != nil {
return nil, err
}
return self, nil
}
func selfSign(priv *rsa.PrivateKey, csr *x509.CertificateRequest) (*x509.Certificate, error) {
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
if err != nil {
return nil, fmt.Errorf("failed to generate serial number: %s", err)
}
notBefore := time.Now()
notAfter := notBefore.Add(time.Hour * 1)
template := x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
CommonName: "SCEP SIGNER",
Organization: csr.Subject.Organization,
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
BasicConstraintsValid: true,
}
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
if err != nil {
return nil, err
}
return x509.ParseCertificate(derBytes)
}
func loadPEMCertFromFile(path string) (*x509.Certificate, error) {
data, err := ioutil.ReadFile(path)
if err != nil {
return nil, err
}
pemBlock, _ := pem.Decode(data)
if pemBlock == nil {
return nil, errors.New("PEM decode failed")
}
if pemBlock.Type != certificatePEMBlockType {
return nil, errors.New("unmatched type or headers")
}
return x509.ParseCertificate(pemBlock.Bytes)
}
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