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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"errors"
"io/ioutil"
"os"
)
const (
rsaPrivateKeyPEMBlockType = "RSA PRIVATE KEY"
)
// create a new RSA private key
func newRSAKey(bits int) (*rsa.PrivateKey, error) {
private, err := rsa.GenerateKey(rand.Reader, bits)
if err != nil {
return nil, err
}
return private, nil
}
// load key if it exists or create a new one
func loadOrMakeKey(path string, rsaBits int) (*rsa.PrivateKey, error) {
file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
if err != nil {
if os.IsExist(err) {
return loadKeyFromFile(path)
}
return nil, err
}
defer file.Close()
// write key
priv, err := newRSAKey(rsaBits)
if err != nil {
return nil, err
}
privBytes := x509.MarshalPKCS1PrivateKey(priv)
pemBlock := &pem.Block{
Type: rsaPrivateKeyPEMBlockType,
Headers: nil,
Bytes: privBytes,
}
if err = pem.Encode(file, pemBlock); err != nil {
return nil, err
}
return priv, nil
}
// load a PEM private key from disk
func loadKeyFromFile(path string) (*rsa.PrivateKey, 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 != rsaPrivateKeyPEMBlockType {
return nil, errors.New("unmatched type or headers")
}
return x509.ParsePKCS1PrivateKey(pemBlock.Bytes)
}
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