restic/server/key.go

287 lines
6.7 KiB
Go

package server
import (
"crypto/rand"
"crypto/sha256"
"encoding/json"
"errors"
"fmt"
"io"
"os"
"os/user"
"time"
"github.com/restic/restic/backend"
"github.com/restic/restic/chunker"
"github.com/restic/restic/crypto"
"github.com/restic/restic/debug"
)
var (
// ErrNoKeyFound is returned when no key for the repository could be decrypted.
ErrNoKeyFound = errors.New("no key could be found")
)
// TODO: figure out scrypt values on the fly depending on the current
// hardware.
const (
scryptN = 65536
scryptR = 8
scryptP = 1
scryptSaltsize = 64
)
// Key represents an encrypted master key for a repository.
type Key struct {
Created time.Time `json:"created"`
Username string `json:"username"`
Hostname string `json:"hostname"`
KDF string `json:"kdf"`
N int `json:"N"`
R int `json:"r"`
P int `json:"p"`
Salt []byte `json:"salt"`
Data []byte `json:"data"`
user *crypto.Key
master *crypto.Key
name string
}
// CreateKey initializes a master key in the given backend and encrypts it with
// the password.
func CreateKey(s *Server, password string) (*Key, error) {
return AddKey(s, password, nil)
}
// OpenKey tries do decrypt the key specified by name with the given password.
func OpenKey(s *Server, name string, password string) (*Key, error) {
k, err := LoadKey(s, name)
if err != nil {
return nil, err
}
// check KDF
if k.KDF != "scrypt" {
return nil, errors.New("only supported KDF is scrypt()")
}
// derive user key
k.user, err = crypto.KDF(k.N, k.R, k.P, k.Salt, password)
if err != nil {
return nil, err
}
// decrypt master keys
buf, err := crypto.Decrypt(k.user, []byte{}, k.Data)
if err != nil {
return nil, err
}
// restore json
k.master = &crypto.Key{}
err = json.Unmarshal(buf, k.master)
if err != nil {
return nil, err
}
k.name = name
if !k.Valid() {
return nil, errors.New("Invalid key for repository")
}
// test if the chunker polynomial is present in the master key
if k.master.ChunkerPolynomial == 0 {
return nil, errors.New("Polynomial for content defined chunking is zero")
}
debug.Log("OpenKey", "Master keys loaded, polynomial %v", k.master.ChunkerPolynomial)
return k, nil
}
// SearchKey tries to decrypt all keys in the backend with the given password.
// If none could be found, ErrNoKeyFound is returned.
func SearchKey(s *Server, password string) (*Key, error) {
// try all keys in repo
done := make(chan struct{})
defer close(done)
for name := range s.List(backend.Key, done) {
key, err := OpenKey(s, name, password)
if err != nil {
continue
}
return key, nil
}
return nil, ErrNoKeyFound
}
// LoadKey loads a key from the backend.
func LoadKey(s *Server, name string) (*Key, error) {
// extract data from repo
rd, err := s.be.Get(backend.Key, name)
if err != nil {
return nil, err
}
defer rd.Close()
// restore json
dec := json.NewDecoder(rd)
k := Key{}
err = dec.Decode(&k)
if err != nil {
return nil, err
}
return &k, nil
}
// AddKey adds a new key to an already existing repository.
func AddKey(s *Server, password string, template *Key) (*Key, error) {
// fill meta data about key
newkey := &Key{
Created: time.Now(),
KDF: "scrypt",
N: scryptN,
R: scryptR,
P: scryptP,
}
hn, err := os.Hostname()
if err == nil {
newkey.Hostname = hn
}
usr, err := user.Current()
if err == nil {
newkey.Username = usr.Username
}
// generate random salt
newkey.Salt = make([]byte, scryptSaltsize)
n, err := rand.Read(newkey.Salt)
if n != scryptSaltsize || err != nil {
panic("unable to read enough random bytes for salt")
}
// call KDF to derive user key
newkey.user, err = crypto.KDF(newkey.N, newkey.R, newkey.P, newkey.Salt, password)
if err != nil {
return nil, err
}
if template == nil {
// generate new random master keys
newkey.master = crypto.NewRandomKey()
// generate random polynomial for cdc
p, err := chunker.RandomPolynomial()
if err != nil {
debug.Log("AddKey", "error generating new polynomial for cdc: %v", err)
return nil, err
}
debug.Log("AddKey", "generated new polynomial for cdc: %v", p)
newkey.master.ChunkerPolynomial = p
} else {
// copy master keys from old key
newkey.master = template.master
}
// encrypt master keys (as json) with user key
buf, err := json.Marshal(newkey.master)
if err != nil {
return nil, err
}
newkey.Data, err = crypto.Encrypt(newkey.user, nil, buf)
// dump as json
buf, err = json.Marshal(newkey)
if err != nil {
return nil, err
}
// store in repository and return
blob, err := s.be.Create()
if err != nil {
return nil, err
}
plainhw := backend.NewHashingWriter(blob, sha256.New())
_, err = plainhw.Write(buf)
if err != nil {
return nil, err
}
name := backend.ID(plainhw.Sum(nil)).String()
err = blob.Finalize(backend.Key, name)
if err != nil {
return nil, err
}
newkey.name = name
return newkey, nil
}
// Encrypt encrypts and authenticates data with the master key. Stored in
// ciphertext is IV || Ciphertext || MAC. Returns the ciphertext, which is
// extended if necessary.
func (k *Key) Encrypt(ciphertext, plaintext []byte) ([]byte, error) {
return crypto.Encrypt(k.master, ciphertext, plaintext)
}
// EncryptTo encrypts and authenticates data with the master key. The returned
// io.Writer writes IV || Ciphertext || MAC.
func (k *Key) EncryptTo(wr io.Writer) io.WriteCloser {
return crypto.EncryptTo(k.master, wr)
}
// Decrypt verifes and decrypts the ciphertext with the master key. Ciphertext
// must be in the form IV || Ciphertext || MAC.
func (k *Key) Decrypt(plaintext, ciphertext []byte) ([]byte, error) {
return crypto.Decrypt(k.master, plaintext, ciphertext)
}
// DecryptFrom verifies and decrypts the ciphertext read from rd and makes it
// available on the returned Reader. Ciphertext must be in the form IV ||
// Ciphertext || MAC. In order to correctly verify the ciphertext, rd is
// drained, locally buffered and made available on the returned Reader
// afterwards. If a MAC verification failure is observed, it is returned
// immediately.
func (k *Key) DecryptFrom(rd io.Reader) (io.ReadCloser, error) {
return crypto.DecryptFrom(k.master, rd)
}
// Master returns the master keys for this repository. Only included for
// debug purposes.
func (k *Key) Master() *crypto.Key {
return k.master
}
// User returns the user keys for this key. Only included for debug purposes.
func (k *Key) User() *crypto.Key {
return k.user
}
func (k *Key) String() string {
if k == nil {
return "<Key nil>"
}
return fmt.Sprintf("<Key of %s@%s, created on %s>", k.Username, k.Hostname, k.Created)
}
func (k Key) Name() string {
return k.name
}
// Valid tests whether the mac and encryption keys are valid (i.e. not zero)
func (k *Key) Valid() bool {
return k.user.Valid() && k.master.Valid()
}