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certificate.go
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certificate.go
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package cert
import (
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"fmt"
"math/big"
"time"
)
const (
DefaultOrgName = "Random Organisation"
DefaultCommonName = "domain.invalid"
DefaultExpiryPeriod = 24 * time.Hour
)
var (
serialNumberLimit = new(big.Int).Lsh(big.NewInt(1), 128)
)
type Options struct {
OrgName string
CommonName string
Expiry time.Time
PrivateKey crypto.PrivateKey
}
func GenerateCert(opts Options) (cert []byte, privKey crypto.PrivateKey) {
if opts.OrgName == "" {
opts.OrgName = DefaultOrgName
}
if opts.CommonName == "" {
opts.CommonName = DefaultCommonName
}
if opts.Expiry.IsZero() {
opts.Expiry = time.Now().Add(DefaultExpiryPeriod)
}
if opts.PrivateKey == nil {
priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
panic(fmt.Sprintf("Failed to generate ECDSA key: %s", err))
}
opts.PrivateKey = priv
}
serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
if err != nil {
panic(fmt.Sprintf("Failed to generate serial number: %s", err))
}
template := x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
Organization: []string{opts.OrgName},
CommonName: opts.CommonName,
},
NotBefore: time.Now(),
NotAfter: opts.Expiry,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
BasicConstraintsValid: true,
}
var pubKey crypto.PublicKey
switch k := opts.PrivateKey.(type) {
case *rsa.PrivateKey:
pubKey = &k.PublicKey
case *ecdsa.PrivateKey:
pubKey = &k.PublicKey
default:
panic("unsupported private key type")
}
derCert, err := x509.CreateCertificate(
rand.Reader, &template, &template, pubKey, opts.PrivateKey)
if err != nil {
panic(fmt.Sprintf("Failed to generate certificate: %s", err))
}
return derCert, opts.PrivateKey
}