1
0
Fork 0
mirror of https://github.com/restic/restic.git synced 2024-12-24 16:54:00 +00:00
restic/key.go
2015-03-22 21:03:01 +01:00

327 lines
8 KiB
Go

package restic
import (
"crypto/rand"
"encoding/json"
"errors"
"fmt"
"io"
"os"
"os/user"
"time"
"github.com/restic/restic/backend"
"github.com/restic/restic/chunker"
"golang.org/x/crypto/poly1305"
)
// max size is 8MiB, defined in chunker
const macSize = poly1305.TagSize // Poly1305 size is 16 byte
const maxCiphertextSize = ivSize + chunker.MaxSize + macSize
const CiphertextExtension = ivSize + macSize
var (
// ErrUnauthenticated is returned when ciphertext verification has failed.
ErrUnauthenticated = errors.New("ciphertext verification failed")
// ErrNoKeyFound is returned when no key for the repository could be decrypted.
ErrNoKeyFound = errors.New("no key could be found")
// ErrBufferTooSmall is returned when the destination slice is too small
// for the ciphertext.
ErrBufferTooSmall = errors.New("destination buffer too small")
)
// 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"`
Comment string `json:"comment,omitempty"`
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 *MasterKeys
master *MasterKeys
id backend.ID
}
// MasterKeys holds signing and encryption keys for a repository. It is stored
// encrypted and signed as a JSON data structure in the Data field of the Key
// structure.
type MasterKeys struct {
Sign MACKey `json:"sign"`
Encrypt AESKey `json:"encrypt"`
}
// 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 id with the given password.
func OpenKey(s Server, id backend.ID, password string) (*Key, error) {
k, err := LoadKey(s, id)
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 = kdf(k, password)
if err != nil {
return nil, err
}
// decrypt master keys
buf, err := k.DecryptUser([]byte{}, k.Data)
if err != nil {
return nil, err
}
// restore json
k.master = &MasterKeys{}
err = json.Unmarshal(buf, k.master)
if err != nil {
return nil, err
}
k.id = id
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) {
// list all keys
ids, err := s.List(backend.Key)
if err != nil {
panic(err)
}
// try all keys in repo
var key *Key
for _, id := range ids {
key, err = OpenKey(s, id, password)
if err != nil {
continue
}
return key, nil
}
return nil, ErrNoKeyFound
}
// LoadKey loads a key from the backend.
func LoadKey(s Server, id backend.ID) (*Key, error) {
// extract data from repo
data, err := s.Get(backend.Key, id)
if err != nil {
return nil, err
}
// restore json
k := &Key{}
err = json.Unmarshal(data, k)
if err != nil {
return nil, err
}
return k, err
}
// 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 = kdf(newkey, password)
if err != nil {
return nil, err
}
if template == nil {
// generate new random master keys
newkey.master = generateRandomKeys()
} 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 = GetChunkBuf("key")
n, err = newkey.EncryptUser(newkey.Data, buf)
newkey.Data = newkey.Data[:n]
// dump as json
buf, err = json.Marshal(newkey)
if err != nil {
return nil, err
}
// store in repository and return
blob, err := s.Create(backend.Key)
if err != nil {
return nil, err
}
_, err = blob.Write(buf)
if err != nil {
return nil, err
}
err = blob.Close()
if err != nil {
return nil, err
}
id, err := blob.ID()
if err != nil {
return nil, err
}
newkey.id = id
FreeChunkBuf("key", newkey.Data)
return newkey, nil
}
func (k *Key) newIV(buf []byte) error {
_, err := io.ReadFull(rand.Reader, buf[:ivSize])
buf = buf[:ivSize]
if err != nil {
return err
}
return nil
}
// EncryptUser encrypts and signs data with the user key. Stored in ciphertext
// is IV || Ciphertext || MAC.
func (k *Key) EncryptUser(ciphertext, plaintext []byte) (int, error) {
return Encrypt(k.user, ciphertext, plaintext)
}
// Encrypt encrypts and signs data with the master key. Stored in ciphertext is
// IV || Ciphertext || MAC. Returns the ciphertext length.
func (k *Key) Encrypt(ciphertext, plaintext []byte) (int, error) {
return Encrypt(k.master, ciphertext, plaintext)
}
// EncryptTo encrypts and signs data with the master key. The returned
// io.Writer writes IV || Ciphertext || HMAC. For the hash function, SHA256 is
// used.
func (k *Key) EncryptTo(wr io.Writer) io.WriteCloser {
return EncryptTo(k.master, wr)
}
// EncryptUserTo encrypts and signs data with the user key. The returned
// io.Writer writes IV || Ciphertext || HMAC. For the hash function, SHA256 is
// used.
func (k *Key) EncryptUserTo(wr io.Writer) io.WriteCloser {
return EncryptTo(k.user, 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 Decrypt(k.master, plaintext, ciphertext)
}
// DecryptUser verifes and decrypts the ciphertext with the user key. Ciphertext
// must be in the form IV || Ciphertext || MAC.
func (k *Key) DecryptUser(plaintext, ciphertext []byte) ([]byte, error) {
return Decrypt(k.user, 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 an MAC verification failure is observed, it is returned
// immediately.
func (k *Key) DecryptFrom(rd io.Reader) (io.ReadCloser, error) {
return DecryptFrom(k.master, rd)
}
// DecryptFrom verifies and decrypts the ciphertext read from rd with the user
// key 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 an MAC verification failure is observed, it is returned
// immediately.
func (k *Key) DecryptUserFrom(rd io.Reader) (io.ReadCloser, error) {
return DecryptFrom(k.user, rd)
}
// Master() returns the master keys for this repository. Only included for
// debug purposes.
func (k *Key) Master() *MasterKeys {
return k.master
}
// User() returns the user keys for this key. Only included for debug purposes.
func (k *Key) User() *MasterKeys {
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) ID() backend.ID {
return k.id
}