local.go

// Copyright 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package store

import (
	"bufio"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"math/big"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"

	"crypto/x509"

	"github.com/google/easypki/pkg/certificate"
)

// Predifined directory names.
const (
	LocalCertsDir = "certs"
	LocalKeysDir  = "keys"
	LocalCrlsDir  = "crls"
)

var (
	// Index format
	// 0 full string
	// 1 Valid/Revoked/Expired
	// 2 Expiration date
	// 3 Revocation date
	// 4 Serial
	// 5 Filename
	// 6 Subject
	indexRegexp = regexp.MustCompile("^(V|R|E)\t([0-9]{12}Z)\t([0-9]{12}Z)?\t([0-9a-fA-F]{2,})\t([^\t]+)\t(.+)")
)

// Local lets us store a Certificate Authority on the local filesystem.
//
// The structure used makes it compatible with openssl.
type Local struct {
	Root string
}

// path returns private and public key path.
func (l *Local) path(caName, name string) (key string, cert string) {
	key = filepath.Join(l.Root, caName, LocalKeysDir, name+".key")
	cert = filepath.Join(l.Root, caName, LocalCertsDir, name+".crt")
	return
}

// Exists checks if a certificate or private key already exist on the local
// filesystem for a given name.
func (l *Local) Exists(caName, name string) bool {
	privPath, certPath := l.path(caName, name)
	if _, err := os.Stat(privPath); err == nil {
		return true
	}
	if _, err := os.Stat(certPath); err == nil {
		return true
	}
	return false
}

// Fetch fetchs the private key and certificate for a given name signed by caName.
func (l *Local) Fetch(caName, name string) ([]byte, []byte, error) {
	filepath.Join(l.Root, caName)

	keyPath, certPath := l.path(caName, name)
	k, err := readPEM(keyPath)
	if err != nil {
		return nil, nil, fmt.Errorf("failed reading CA private key from file %v: %v", keyPath, err)
	}
	c, err := readPEM(certPath)
	if err != nil {
		return nil, nil, fmt.Errorf("failed reading CA cert from file %v: %v", certPath, err)
	}
	return k, c, nil
}

func readPEM(path string) ([]byte, error) {
	bytes, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("failed reading %v: %v", path, err)
	}
	p, _ := pem.Decode(bytes)
	if p == nil {
		return nil, fmt.Errorf("no PEM data found for certificate")
	}
	return p.Bytes, nil
}

// Add adds the given bundle to the local filesystem.
func (l *Local) Add(caName, name string, isCa bool, key, cert []byte) error {
	if l.Exists(caName, name) {
		return fmt.Errorf("a bundle already exists for the name %v within CA %v", name, caName)
	}
	if err := l.writeBundle(caName, name, isCa, key, cert); err != nil {
		return fmt.Errorf("failed writing bundle %v within CA %v to the local filesystem: %v", name, caName, err)
	}
	if err := l.updateIndex(caName, name, cert); err != nil {
		return fmt.Errorf("failed updating CA %v index: %v", caName, err)
	}
	return nil
}

// writeBundle encodes in PEM format the bundle private key and
// certificate and stores them on the local filesystem.
func (l *Local) writeBundle(caName, name string, isCa bool, key, cert []byte) error {
	caDir := filepath.Join(l.Root, caName)
	if _, err := os.Stat(caDir); err != nil {
		if err := InitCADir(caDir); err != nil {
			return fmt.Errorf("root directory for CA %v does not exist and cannot be created: %v", caDir, err)
		}
	}
	keyPath, certPath := l.path(caName, name)
	if err := encodeAndWrite(keyPath, "RSA PRIVATE KEY", key); err != nil {
		return fmt.Errorf("failed encoding and writing private key file: %v", err)
	}
	if err := encodeAndWrite(certPath, "CERTIFICATE", cert); err != nil {
		return fmt.Errorf("failed encoding and writing cert file: %v", err)
	}

	if isCa && name != caName {
		intCaDir := filepath.Join(l.Root, name)
		if err := InitCADir(intCaDir); err != nil {
			return fmt.Errorf("root directory for CA %v does not exist and cannot be created: %v", intCaDir, err)
		}
		kp, cp := l.path(name, name)
		if err := os.Link(keyPath, kp); err != nil {
			return fmt.Errorf("failed creating hard link from %v to %v: %v", keyPath, kp, err)
		}
		if err := os.Link(certPath, cp); err != nil {
			return fmt.Errorf("failed creating hard link from %v to %v: %v", certPath, cp, err)
		}
	}
	return nil
}

func encodeAndWrite(path, pemType string, data []byte) error {
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	defer f.Close()

	return pem.Encode(f, &pem.Block{
		Type:  pemType,
		Bytes: data,
	})
}

// updateIndex appends a line to the index.txt with few information about the
// given the certificate.
func (l *Local) updateIndex(caName, name string, rawCert []byte) error {
	f, err := os.OpenFile(filepath.Join(l.Root, caName, "index.txt"), os.O_WRONLY|os.O_APPEND, 0644)
	if err != nil {
		return err
	}
	defer f.Close()

	cert, err := x509.ParseCertificate(rawCert)
	if err != nil {
		return fmt.Errorf("failed parsing raw certificate %v: %v", name, err)
	}

	sn := fmt.Sprintf("%X", cert.SerialNumber)
	// For compatibility with openssl we need an even length.
	if len(sn)%2 == 1 {
		sn = "0" + sn
	}

	// Date format: yymmddHHMMSSZ
	// E|R|V<tab>Expiry<tab>[RevocationDate]<tab>Serial<tab>filename<tab>SubjectDN
	var subject string
	if strs := cert.Subject.Country; len(strs) == 1 {
		subject += "/C=" + strs[0]
	}
	if strs := cert.Subject.Organization; len(strs) == 1 {
		subject += "/O=" + strs[0]
	}
	if strs := cert.Subject.OrganizationalUnit; len(strs) == 1 {
		subject += "/OU=" + strs[0]
	}
	if strs := cert.Subject.Locality; len(strs) == 1 {
		subject += "/L=" + strs[0]
	}
	if strs := cert.Subject.Province; len(strs) == 1 {
		subject += "/ST=" + strs[0]
	}
	subject += "/CN=" + cert.Subject.CommonName

	n, err := fmt.Fprintf(f, "V\t%vZ\t\t%v\t%v.crt\t%v\n",
		cert.NotAfter.UTC().Format("060102150405"),
		sn,
		name,
		subject)
	if err != nil {
		return err
	}
	if n == 0 {
		return fmt.Errorf("written 0 bytes in index file")
	}
	return nil
}

// Update updates the state of a given certificate in the index.txt.
func (l *Local) Update(caName string, sn *big.Int, st certificate.State) error {
	f, err := os.OpenFile(filepath.Join(l.Root, caName, "index.txt"), os.O_RDWR, 0644)
	if err != nil {
		return err
	}
	defer f.Close()

	var state string
	switch st {
	case certificate.Valid:
		state = "V"
	case certificate.Revoked:
		state = "R"
	case certificate.Expired:
		state = "E"
	default:
		return fmt.Errorf("unhandled certificate state: %v", st)
	}

	var lines []string
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		matches := indexRegexp.FindStringSubmatch(scanner.Text())
		if len(matches) != 7 {
			return fmt.Errorf("line [%v] is incorrectly formated", scanner.Text())
		}

		matchedSerial := big.NewInt(0)
		fmt.Sscanf(matches[4], "%X", matchedSerial)
		if matchedSerial.Cmp(sn) == 0 {
			if matches[1] == state {
				return nil
			}

			lines = append(lines, fmt.Sprintf("%v\t%v\t%vZ\t%v\t%v\t%v",
				state,
				matches[2],
				time.Now().UTC().Format("060102150405"),
				matches[4],
				matches[5],
				matches[6]))
		} else {
			lines = append(lines, matches[0])
		}
	}

	f.Truncate(0)
	f.Seek(0, 0)

	for _, line := range lines {
		n, err := fmt.Fprintln(f, line)
		if err != nil {
			return fmt.Errorf("failed writing line [%v]: %v", line, err)
		}
		if n == 0 {
			return fmt.Errorf("failed writing line [%v]: written 0 bytes", line)
		}
	}
	return nil
}

// Revoked returns a list of revoked certificates.
func (l *Local) Revoked(caName string) ([]pkix.RevokedCertificate, error) {
	index, err := os.Open(filepath.Join(l.Root, caName, "index.txt"))
	if err != nil {
		return nil, err
	}
	defer index.Close()

	var revokedCerts []pkix.RevokedCertificate
	scanner := bufio.NewScanner(index)
	for scanner.Scan() {
		matches := indexRegexp.FindStringSubmatch(scanner.Text())
		if len(matches) != 7 {
			return nil, fmt.Errorf("line [%v] is incorrectly formated", scanner.Text())
		}
		if matches[1] != "R" {
			continue
		}

		sn := big.NewInt(0)
		fmt.Sscanf(matches[4], "%X", sn)
		t, err := time.Parse("060102150405", strings.TrimSuffix(matches[3], "Z"))
		if err != nil {
			return nil, fmt.Errorf("failed parsing revocation time %v: %v", matches[3], err)
		}
		revokedCerts = append(revokedCerts, pkix.RevokedCertificate{
			SerialNumber:   sn,
			RevocationTime: t,
		})
	}
	return revokedCerts, nil
}

// InitCADir creates the basic structure of a CA subdirectory.
//
//   |- crlnumber
//   |- index.txt
//   |- index.txt.attr
//   |- serial
//   |- certs/
//     |- ca.crt
//     |- name.crt
//   |- keys/
//     |- ca.key
//     |- name.key
func InitCADir(path string) error {
	if _, err := os.Stat(path); err == nil {
		return nil
	}
	if err := os.Mkdir(path, 0755); err != nil {
		return fmt.Errorf("failed creating CA root directory %v: %v", path, err)
	}
	dirs := map[string]os.FileMode{
		filepath.Join(path, LocalCrlsDir):  0700,
		filepath.Join(path, LocalCertsDir): 0755,
		filepath.Join(path, LocalKeysDir):  0700,
	}
	for d, m := range dirs {
		if err := os.Mkdir(d, m); err != nil {
			return fmt.Errorf("failed creating directory %v: %v", d, err)
		}
	}

	files := []struct {
		Name    string
		Content string
	}{
		{Name: "serial", Content: "01"},
		{Name: "crlnumber", Content: "01"},
		{Name: "index.txt", Content: ""},
		{Name: "index.txt.attr", Content: "unique_subject = no"},
	}
	for _, f := range files {
		if err := createFile(filepath.Join(path, f.Name), f.Content); err != nil {
			return err
		}
	}
	return nil
}

func createFile(path, content string) error {
	fh, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("failed creating file  %v: %v", path, err)
	}
	defer fh.Close()

	if content == "" {
		return nil
	}

	n, err := fmt.Fprintln(fh, content)
	if err != nil {
		return fmt.Errorf("failed wrinting %v in %v: %v", content, path, err)
	}
	if n == 0 {
		return fmt.Errorf("failed writing %v in %v: 0 bytes written", content, path)
	}
	return nil
}