key.go

package ssh

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"os"

	"github.com/jcelliott/lumber"
	"golang.org/x/crypto/ssh"
)

// GetKeyPair will attempt to get the keypair from a file and will fail back
// to generating a new set and saving it to the file. Returns pub, priv, err
func GetKeyPair(file string) (string, string, error) {
	// read keys from file
	_, err := os.Stat(file)
	if err == nil {
		priv, err := ioutil.ReadFile(file)
		if err != nil {
			lumber.Debug("Failed to read file - %s", err)
			goto genKeys
		}
		pub, err := ioutil.ReadFile(file + ".pub")
		if err != nil {
			lumber.Debug("Failed to read pub file - %s", err)
			goto genKeys
		}
		return string(pub), string(priv), nil
	}

	// generate keys and save to file
genKeys:
	pub, priv, err := GenKeyPair()
	err = ioutil.WriteFile(file, []byte(priv), 0600)
	if err != nil {
		return "", "", fmt.Errorf("Failed to write file - %s", err)
	}
	err = ioutil.WriteFile(file+".pub", []byte(pub), 0644)
	if err != nil {
		return "", "", fmt.Errorf("Failed to write pub file - %s", err)
	}

	return pub, priv, nil
}

// GenKeyPair make a pair of public and private keys for SSH access.
// Public key is encoded in the format for inclusion in an OpenSSH authorized_keys file.
// Private Key generated is PEM encoded
func GenKeyPair() (string, string, error) {
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return "", "", err
	}

	privateKeyPEM := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)}
	var private bytes.Buffer
	if err := pem.Encode(&private, privateKeyPEM); err != nil {
		return "", "", err
	}

	// generate public key
	pub, err := ssh.NewPublicKey(&privateKey.PublicKey)
	if err != nil {
		return "", "", err
	}

	public := ssh.MarshalAuthorizedKey(pub)
	return string(public), private.String(), nil
}