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cert.go
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cert.go
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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"math/big"
"net"
"sync"
"time"
)
const RSABits = 2048
const ValidFor = time.Hour * 1440
var certCache sync.Map
func GetSelfSignedCertificate(clientHello *tls.ClientHelloInfo) (*tls.Certificate, error) {
if cert, ok := certCache.Load(clientHello.ServerName); ok {
return cert.(*tls.Certificate), nil
}
priv, err := rsa.GenerateKey(rand.Reader, RSABits)
if err != nil {
return nil, err
}
notBefore := time.Now()
notAfter := notBefore.Add(ValidFor)
serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
if err != nil {
return nil, err
}
template := x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
Organization: []string{"Acme Co"},
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
BasicConstraintsValid: true,
}
host := clientHello.ServerName
if ip := net.ParseIP(host); ip != nil {
template.IPAddresses = append(template.IPAddresses, ip)
} else {
template.DNSNames = append(template.DNSNames, host)
}
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
if err != nil {
return nil, err
}
cert := &tls.Certificate{
Certificate: [][]byte{derBytes},
PrivateKey: priv,
}
certCache.Store(clientHello.ServerName, cert)
return cert, err
}