github.com/david-imola/snapd@v0.0.0-20210611180407-2de8ddeece6d/overlord/devicestate/crypto.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  /*
     3   * Copyright (C) 2016-2017 Canonical Ltd
     4   *
     5   * This program is free software: you can redistribute it and/or modify
     6   * it under the terms of the GNU General Public License version 3 as
     7   * published by the Free Software Foundation.
     8   *
     9   * This program is distributed in the hope that it will be useful,
    10   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    11   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    12   * GNU General Public License for more details.
    13   *
    14   * You should have received a copy of the GNU General Public License
    15   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    16   *
    17   */
    18  
    19  package devicestate
    20  
    21  import (
    22  	"crypto/rsa"
    23  	"crypto/x509"
    24  	"encoding/pem"
    25  	"errors"
    26  	"io/ioutil"
    27  	"os"
    28  	"os/exec"
    29  	"path/filepath"
    30  	"strconv"
    31  
    32  	"github.com/snapcore/snapd/osutil"
    33  )
    34  
    35  func generateRSAKey(keyLength int) (*rsa.PrivateKey, error) {
    36  	// The temporary directory is created with mode
    37  	// 0700 by ioutil.TempDir, see:
    38  	//   https://github.com/golang/go/blob/master/src/io/ioutil/tempfile.go#L84
    39  	tempDir, err := ioutil.TempDir(os.TempDir(), "snapd")
    40  	if err != nil {
    41  		return nil, err
    42  	}
    43  
    44  	defer os.RemoveAll(tempDir)
    45  
    46  	rsaKeyFile := filepath.Join(tempDir, "rsa.key")
    47  
    48  	cmd := exec.Command("ssh-keygen", "-t", "rsa", "-b", strconv.Itoa(keyLength), "-N", "", "-f", rsaKeyFile, "-m", "PEM")
    49  	out, err := cmd.CombinedOutput()
    50  	if err != nil {
    51  		return nil, osutil.OutputErr(out, err)
    52  	}
    53  
    54  	d, err := ioutil.ReadFile(rsaKeyFile)
    55  	if err != nil {
    56  		return nil, err
    57  	}
    58  
    59  	blk, _ := pem.Decode(d)
    60  	if blk == nil {
    61  		return nil, errors.New("cannot decode PEM block")
    62  	}
    63  
    64  	key, err := x509.ParsePKCS1PrivateKey(blk.Bytes)
    65  	if err != nil {
    66  		return nil, err
    67  	}
    68  
    69  	err = key.Validate()
    70  	if err != nil {
    71  		return nil, err
    72  	}
    73  
    74  	err = os.RemoveAll(tempDir)
    75  	if err != nil {
    76  		return nil, err
    77  	}
    78  
    79  	return key, err
    80  }