package main

import (
	"crypto/rsa"
	"fmt"
	"crypto/x509"
	"encoding/pem"
	"os"
	"crypto/rand"
	"flag"
)

func main(){
	var keyfilename string
	var keylen int
	var help bool
	flag.IntVar(&keylen, "l", 2048, "Key Length (default: 2048)")
	flag.StringVar(&keyfilename, "o", "sshhost.key", "Output File Name (default: sshhost.key)")
	flag.BoolVar(&help, "h", false, "Show Help")
	if help{
		fmt.Println("Usage: HostKeyGen [-h] [-l <keylenth>] [-o <out_file>]")
		flag.PrintDefaults()
		return
	}
	GenerateRSAKey(keyfilename, keylen)
}

func GenerateRSAKey(keyfn string,keyLength int) {
	privateKey, err := rsa.GenerateKey(rand.Reader, keyLength)
	if err != nil {
		fmt.Println("Failed to Generate RSA Private Key: ", err)
		return
	}
	derStream := x509.MarshalPKCS1PrivateKey(privateKey)
	block := &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: derStream,
	}
	file, err := os.Create(keyfn)
	if err != nil {
		fmt.Println("Failed to Create Key File: ", err)
		return
	}
	err = pem.Encode(file, block)
	if err != nil {
		fmt.Println("Failed to Encode Key: ", err)
		return
	}
	fmt.Println("SSH Host Key Generated Successfully..")
}