Generate ed25519 keys in PEM format using Go

ed25519genandsave.go

// RCL 05 June 2021

/*
verify with `openssl pkey -in <privatekey>` or `openssl pkey -in <privatekey> -pubout`
the latter should match the publickey
*/

package main

import (
	"crypto/ed25519"
	"crypto/rand"
	"crypto/x509"
	"encoding/pem"
	"io/ioutil"

	"fmt"
	"os"
)

// GenerateSaveEd25519 generates and saves ed25519 keys to disk after
// encoding into PEM format
func GenerateSaveEd25519(fb string) error {

	var (
		err   error
		b     []byte
		block *pem.Block
		pub   ed25519.PublicKey
		priv  ed25519.PrivateKey
	)

	pub, priv, err = ed25519.GenerateKey(rand.Reader)
	if err != nil {
		fmt.Printf("Generation error : %s", err)
		os.Exit(1)
	}

	b, err = x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		return err
	}

	block = &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: b,
	}

	err = ioutil.WriteFile(fb, pem.EncodeToMemory(block), 0600)
	if err != nil {
		return err
	}

	// public key
	b, err = x509.MarshalPKIXPublicKey(pub)
	if err != nil {
		return err
	}

	block = &pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: b,
	}

	fileName := fb + ".pub"
	err = ioutil.WriteFile(fileName, pem.EncodeToMemory(block), 0644)
	return err

}

func main() {

	if len(os.Args) != 2 || os.Args[1] == "-h" || os.Args[1] == "--help" {
		fmt.Printf("%s : generate pem formatted ed25519 keys\n", os.Args[0])
		fmt.Println("    provide a single argument for the private key name")
		fmt.Println("    the public key name will have '.pub' appended")
		os.Exit(1)
	}

	FileBaseName := os.Args[1]

	if err := GenerateSaveEd25519(FileBaseName); err != nil {
		fmt.Printf("Error : %s\n", err)
		os.Exit(1)
	}
}