pem.go

package util

// util
// Copyright (C) 2018 Maximilian Pachl

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

// ---------------------------------------------------------------------------------------
//  imports
// ---------------------------------------------------------------------------------------

import (
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"io/ioutil"
)

// ---------------------------------------------------------------------------------------
//  errors
// ---------------------------------------------------------------------------------------

var (
	ErrKeyMustBePEMEncoded = errors.New("must be PEM encoded PKCS1 or PKCS8 private key")
	ErrNotRSAPrivateKey    = errors.New("not a valid RSA private key")
)

// ---------------------------------------------------------------------------------------
//  public functions
// ---------------------------------------------------------------------------------------

// ReadRSAPemKey read the PEM encoded RSA private key from the filesystem.
func ReadRSAPemKey(path string) (*rsa.PrivateKey, error) {
	var err error

	key, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, err
	}

	// Parse PEM block
	var block *pem.Block
	if block, _ = pem.Decode(key); block == nil {
		return nil, ErrKeyMustBePEMEncoded
	}

	var parsedKey interface{}
	if parsedKey, err = x509.ParsePKCS1PrivateKey(block.Bytes); err != nil {
		if parsedKey, err = x509.ParsePKCS8PrivateKey(block.Bytes); err != nil {
			return nil, err
		}
	}

	var pkey *rsa.PrivateKey
	var ok bool
	if pkey, ok = parsedKey.(*rsa.PrivateKey); !ok {
		return nil, ErrNotRSAPrivateKey
	}

	return pkey, nil

}