Storing and retrieving RSA encryption key - json

Question

I am trying to build an API, but to secure it properly I believe I need to go with RSA encryption for a private key stored on my server and a public key for the client. I have stored the generated private key into a JSON file, I plan to store on my server but to write to JSON, I needed to convert the type too []byte. Now when I try to retrieve the private key to generate a public key, but it will not let me use type bytes for *Publickey
The only other way I can think of to accomplish this goal is to seed the random number generator, so I can have the seed a secret on my server and then my private key should always generate to the same thing, any help this this would be great.
package main
import (
"bytes"
"crypto/rand"
"crypto/rsa"
"encoding/json"
"fmt"
"io/ioutil"
"os"
)
func main() {
mimicPrivateKey, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
fmt.Println(err)
os.Exit(1)
}
buf := new(bytes.Buffer)
json.NewEncoder(buf).Encode(mimicPrivateKey)
secrets, _ := os.OpenFile("secrets.json", os.O_RDWR|os.O_APPEND|os.O_CREATE, 0666)
// Close the secrets file when the surrounding function exists
secrets.WriteString(buf.String())
secrets.Close()
secrets, _ = os.OpenFile("secrets.json", os.O_RDWR, 0666)
serverKey, _ := ioutil.ReadAll(secrets)
if serverKey != nil {
fmt.Println("can not open key")
}
serverKeyPublic := &serverKey.PublicKey
}

Answer 1

You need to Unmarshal it:
var data *rsa.PrivateKey
err = json.Unmarshal(serverKey, &data)
if err != nil {
panic(err)
}
And you may use
err = ioutil.WriteFile("secrets.json", buf.Bytes(), 0666)
and
serverKey, err := ioutil.ReadFile("secrets.json")
See:
package main
import (
"bytes"
"crypto/rand"
"crypto/rsa"
"encoding/json"
"fmt"
"io/ioutil"
)
func main() {
mimicPrivateKey, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
panic(err)
}
var buf bytes.Buffer
err = json.NewEncoder(&buf).Encode(mimicPrivateKey)
if err != nil {
panic(err)
}
err = ioutil.WriteFile("secrets.json", buf.Bytes(), 0666)
if err != nil {
panic(err)
}
serverKey, err := ioutil.ReadFile("secrets.json")
if err != nil {
panic(err)
}
var data *rsa.PrivateKey
err = json.Unmarshal(serverKey, &data)
if err != nil {
panic(err)
}
serverKeyPublic := data.PublicKey
fmt.Println(serverKeyPublic)
}