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 *keys master *keys 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 keys struct { Sign *MACKey Encrypt *AESKey } // 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 = &keys{} 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 = newkey.newKeys() } 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) newKeys() *keys { return &keys{ Encrypt: generateRandomAESKey(), Sign: generateRandomMACKey(), } } 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) } func (k *Key) String() string { if k == nil { return "" } return fmt.Sprintf("", k.Username, k.Hostname, k.Created) } func (k Key) ID() backend.ID { return k.id }