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certgen.go
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certgen.go
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package util
import (
"bytes"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
_ "crypto/sha512" // Needed for RegisterHash in init
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"errors"
"fmt"
"math/big"
"net"
"os"
"time"
)
// NewTLSCertPair returns a new PEM-encoded x.509 certificate pair based on a 521-bit ECDSA private key. The machine's
// local interface addresses and all variants of IPv4 and IPv6 localhost are included as valid IP addresses.
func NewTLSCertPair(organization string, validUntil time.Time, extraHosts []string) (cert, key []byte, e error) {
now := time.Now()
if validUntil.Before(now) {
return nil, nil, errors.New("validUntil would create an already-expired certificate")
}
priv, e := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
if e != nil {
return nil, nil, e
}
// end of ASN.1 time
endOfTime := time.Date(2049, 12, 31, 23, 59, 59, 0, time.UTC)
if validUntil.After(endOfTime) {
validUntil = endOfTime
}
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
serialNumber, e := rand.Int(rand.Reader, serialNumberLimit)
if e != nil {
return nil, nil, fmt.Errorf("failed to generate serial number: %s", e)
}
host, e := os.Hostname()
if e != nil {
return nil, nil, e
}
ipAddresses := []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("::1")}
dnsNames := []string{host}
if host != "localhost" {
dnsNames = append(dnsNames, "localhost")
}
addIP := func(ipAddr net.IP) {
for _, ip := range ipAddresses {
if ip.Equal(ipAddr) {
return
}
}
ipAddresses = append(ipAddresses, ipAddr)
}
addHost := func(host string) {
for _, dnsName := range dnsNames {
if host == dnsName {
return
}
}
dnsNames = append(dnsNames, host)
}
addrs, e := interfaceAddrs()
if e != nil {
return nil, nil, e
}
for _, a := range addrs {
var ipAddr net.IP
ipAddr, _, e = net.ParseCIDR(a.String())
if e == nil {
addIP(ipAddr)
}
}
for _, hostStr := range extraHosts {
host, _, e = net.SplitHostPort(hostStr)
if e != nil {
host = hostStr
}
if ip := net.ParseIP(host); ip != nil {
addIP(ip)
} else {
addHost(host)
}
}
template := x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
Organization: []string{organization},
CommonName: host,
},
NotBefore: now.Add(-time.Hour * 24),
NotAfter: validUntil,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature |
x509.KeyUsageCertSign,
IsCA: true, // so can sign self.
BasicConstraintsValid: true,
DNSNames: dnsNames,
IPAddresses: ipAddresses,
}
derBytes, e := x509.CreateCertificate(
rand.Reader, &template,
&template, &priv.PublicKey, priv,
)
if e != nil {
return nil, nil, fmt.Errorf("failed to create certificate: %v", e)
}
certBuf := &bytes.Buffer{}
e = pem.Encode(certBuf, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
if e != nil {
return nil, nil, fmt.Errorf("failed to encode certificate: %v", e)
}
keybytes, e := x509.MarshalECPrivateKey(priv)
if e != nil {
return nil, nil, fmt.Errorf("failed to marshal private key: %v", e)
}
keyBuf := &bytes.Buffer{}
e = pem.Encode(keyBuf, &pem.Block{Type: "EC PRIVATE KEY", Bytes: keybytes})
if e != nil {
return nil, nil, fmt.Errorf("failed to encode private key: %v", e)
}
return certBuf.Bytes(), keyBuf.Bytes(), nil
}