restic/internal/repository/key.go

286 lines
6.6 KiB
Go

package repository
import (
"context"
"encoding/json"
"fmt"
"os"
"os/user"
"time"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/restic"
"github.com/restic/restic/internal/backend"
"github.com/restic/restic/internal/crypto"
"github.com/restic/restic/internal/debug"
)
var (
// ErrNoKeyFound is returned when no key for the repository could be decrypted.
ErrNoKeyFound = errors.Fatal("wrong password or no key found")
// ErrMaxKeysReached is returned when the maximum number of keys was checked and no key could be found.
ErrMaxKeysReached = errors.Fatal("maximum number of keys reached")
)
// 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
}
// Params tracks the parameters used for the KDF. If not set, it will be
// calibrated on the first run of AddKey().
var Params *crypto.Params
var (
// KDFTimeout specifies the maximum runtime for the KDF.
KDFTimeout = 500 * time.Millisecond
// KDFMemory limits the memory the KDF is allowed to use.
KDFMemory = 60
)
// createMasterKey creates a new master key in the given backend and encrypts
// it with the password.
func createMasterKey(s *Repository, password string) (*Key, error) {
return AddKey(context.TODO(), s, password, nil)
}
// OpenKey tries do decrypt the key specified by name with the given password.
func OpenKey(ctx context.Context, s *Repository, name string, password string) (*Key, error) {
k, err := LoadKey(ctx, s, name)
if err != nil {
debug.Log("LoadKey(%v) returned error %v", name, err)
return nil, err
}
// check KDF
if k.KDF != "scrypt" {
return nil, errors.New("only supported KDF is scrypt()")
}
// derive user key
params := crypto.Params{
N: k.N,
R: k.R,
P: k.P,
}
k.user, err = crypto.KDF(params, k.Salt, password)
if err != nil {
return nil, errors.Wrap(err, "crypto.KDF")
}
// decrypt master keys
nonce, ciphertext := k.Data[:k.user.NonceSize()], k.Data[k.user.NonceSize():]
buf, err := k.user.Open(nil, nonce, ciphertext, nil)
if err != nil {
return nil, err
}
// restore json
k.master = &crypto.Key{}
err = json.Unmarshal(buf, k.master)
if err != nil {
debug.Log("Unmarshal() returned error %v", err)
return nil, errors.Wrap(err, "Unmarshal")
}
k.name = name
if !k.Valid() {
return nil, errors.New("Invalid key for repository")
}
return k, nil
}
// SearchKey tries to decrypt at most maxKeys keys in the backend with the
// given password. If none could be found, ErrNoKeyFound is returned. When
// maxKeys is reached, ErrMaxKeysReached is returned. When setting maxKeys to
// zero, all keys in the repo are checked.
func SearchKey(ctx context.Context, s *Repository, password string, maxKeys int) (k *Key, err error) {
checked := 0
listCtx, cancel := context.WithCancel(ctx)
defer cancel()
// try at most maxKeys keys in repo
err = s.Backend().List(listCtx, restic.KeyFile, func(fi restic.FileInfo) error {
if maxKeys > 0 && checked > maxKeys {
return ErrMaxKeysReached
}
_, err := restic.ParseID(fi.Name)
if err != nil {
debug.Log("rejecting key with invalid name: %v", fi.Name)
return nil
}
debug.Log("trying key %q", fi.Name)
key, err := OpenKey(ctx, s, fi.Name, password)
if err != nil {
debug.Log("key %v returned error %v", fi.Name, err)
// ErrUnauthenticated means the password is wrong, try the next key
if errors.Cause(err) == crypto.ErrUnauthenticated {
return nil
}
return err
}
debug.Log("successfully opened key %v", fi.Name)
k = key
cancel()
return nil
})
if err == context.Canceled {
err = nil
}
if err != nil {
return nil, err
}
if k == nil {
return nil, ErrNoKeyFound
}
return k, nil
}
// LoadKey loads a key from the backend.
func LoadKey(ctx context.Context, s *Repository, name string) (k *Key, err error) {
h := restic.Handle{Type: restic.KeyFile, Name: name}
data, err := backend.LoadAll(ctx, s.be, h)
if err != nil {
return nil, err
}
k = &Key{}
err = json.Unmarshal(data, k)
if err != nil {
return nil, errors.Wrap(err, "Unmarshal")
}
return k, nil
}
// AddKey adds a new key to an already existing repository.
func AddKey(ctx context.Context, s *Repository, password string, template *crypto.Key) (*Key, error) {
// make sure we have valid KDF parameters
if Params == nil {
p, err := crypto.Calibrate(KDFTimeout, KDFMemory)
if err != nil {
return nil, errors.Wrap(err, "Calibrate")
}
Params = &p
debug.Log("calibrated KDF parameters are %v", p)
}
// fill meta data about key
newkey := &Key{
Created: time.Now(),
KDF: "scrypt",
N: Params.N,
R: Params.R,
P: Params.P,
}
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, err = crypto.NewSalt()
if err != nil {
panic("unable to read enough random bytes for salt: " + err.Error())
}
// call KDF to derive user key
newkey.user, err = crypto.KDF(*Params, newkey.Salt, password)
if err != nil {
return nil, err
}
if template == nil {
// generate new random master keys
newkey.master = crypto.NewRandomKey()
} else {
// copy master keys from old key
newkey.master = template
}
// encrypt master keys (as json) with user key
buf, err := json.Marshal(newkey.master)
if err != nil {
return nil, errors.Wrap(err, "Marshal")
}
nonce := crypto.NewRandomNonce()
ciphertext := make([]byte, 0, len(buf)+newkey.user.Overhead()+newkey.user.NonceSize())
ciphertext = append(ciphertext, nonce...)
ciphertext = newkey.user.Seal(ciphertext, nonce, buf, nil)
newkey.Data = ciphertext
// dump as json
buf, err = json.Marshal(newkey)
if err != nil {
return nil, errors.Wrap(err, "Marshal")
}
// store in repository and return
h := restic.Handle{
Type: restic.KeyFile,
Name: restic.Hash(buf).String(),
}
err = s.be.Save(ctx, h, restic.NewByteReader(buf))
if err != nil {
return nil, err
}
newkey.name = h.Name
return newkey, nil
}
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)
}
// Name returns an identifier for the key.
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()
}