/
generator.go
159 lines (132 loc) · 3.44 KB
/
generator.go
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package generator
import (
"bytes"
crand "crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"math/big"
"math/rand"
"time"
"github.com/caiofilipini/certgen/cert"
)
type pemBlock string
const (
pemBlockCertificate = pemBlock("CERTIFICATE")
pemBlockRSAPrivateKey = pemBlock("RSA PRIVATE KEY")
)
var (
emptyCert = cert.Certificate{}
)
// Generator generates self-signed TLS certificates.
type Generator struct {
keySize uint64
orgName string
validity time.Duration
}
// CertOpt is used to configure different options for the
// Generator.
type CertOpt func(g *Generator)
// WithOrgName configures the Generator to use the given orgName
// when generating certificates.
func WithOrgName(orgName string) CertOpt {
return func(g *Generator) {
g.orgName = orgName
}
}
// WithKeySize configures the Generator to generate keys with
// `keySize` bits.
func WithKeySize(keySize uint64) CertOpt {
return func(g *Generator) {
g.keySize = keySize
}
}
// WithValidityInDays configures the Generator to generate
// certificates that are valid for `validityInDays` days.
func WithValidityInDays(validityInDays uint64) CertOpt {
return func(g *Generator) {
g.validity = daysToDuration(validityInDays)
}
}
// New creates and returns a new Generator based in the given `opts`.
func New(opts ...CertOpt) *Generator {
gen := &Generator{
orgName: cert.DefaultOrgName,
keySize: cert.DefaultKeySize,
validity: daysToDuration(cert.DefaultCertValidityInDays),
}
for _, opt := range opts {
opt(gen)
}
return gen
}
// NewTLS generates a self-signed TLS certificate with a newly created
// private key, and returns both the cert and the private key PEM encoded.
func (g *Generator) NewTLS() (cert.Certificate, error) {
validityStart := time.Now()
validityEnd := validityStart.Add(g.validity)
certTemplate := &x509.Certificate{
SerialNumber: big.NewInt(int64(randInt())),
Subject: pkix.Name{
Organization: []string{g.orgName},
},
NotBefore: validityStart,
NotAfter: validityEnd,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{
x509.ExtKeyUsageServerAuth,
},
BasicConstraintsValid: true,
}
pk, pkPEM, err := genPrivateKey(g.keySize)
if err != nil {
return emptyCert, err
}
c, err := x509.CreateCertificate(crand.Reader, certTemplate, certTemplate, &pk.PublicKey, pk)
if err != nil {
return emptyCert, err
}
certPEM, err := toPEMString(pemBlockCertificate, c)
if err != nil {
return emptyCert, err
}
return cert.Certificate{
OrgName: g.orgName,
CertPEM: certPEM,
PrivateKeyPEM: pkPEM,
NotBefore: validityStart,
NotAfter: validityEnd,
}, nil
}
func genPrivateKey(size uint64) (*rsa.PrivateKey, string, error) {
pk, err := rsa.GenerateKey(crand.Reader, int(size))
if err != nil {
return nil, "", err
}
pkPEM, err := toPEMString(pemBlockRSAPrivateKey, x509.MarshalPKCS1PrivateKey(pk))
if err != nil {
return nil, "", err
}
return pk, pkPEM, nil
}
func toPEMString(blockType pemBlock, b []byte) (string, error) {
pb := &pem.Block{
Type: string(blockType),
Bytes: b,
}
var buf bytes.Buffer
if err := pem.Encode(&buf, pb); err != nil {
return "", err
}
return buf.String(), nil
}
func randInt() int {
return rand.New(rand.NewSource(time.Now().UnixNano())).Int()
}
func daysToDuration(d uint64) time.Duration {
if d == 0 {
d = cert.DefaultCertValidityInDays
}
return time.Duration(d) * time.Hour * 24
}