package restic import ( "crypto/aes" "crypto/cipher" "crypto/hmac" "crypto/rand" "crypto/sha256" "encoding/json" "errors" "fmt" "hash" "io" "io/ioutil" "os" "os/user" "sync" "time" "github.com/restic/restic/backend" "github.com/restic/restic/chunker" "golang.org/x/crypto/scrypt" ) // max size is 8MiB, defined in chunker const ivSize = aes.BlockSize const hmacSize = sha256.Size const maxCiphertextSize = ivSize + chunker.MaxSize + hmacSize const CiphertextExtension = ivSize + hmacSize 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 aesKeysize = 32 // for AES256 hmacKeysize = 32 // for HMAC with SHA256 ) // 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 } // keys is a JSON structure that holds signing and encryption keys. type keys struct { Sign []byte Encrypt []byte } // 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) { // 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 } // check KDF if k.KDF != "scrypt" { return nil, errors.New("only supported KDF is scrypt()") } // derive user key k.user, err = k.scrypt(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 } // 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 scrypt() to derive user key newkey.user, err = newkey.scrypt(password) if err != nil { return nil, err } if template == nil { // generate new random master keys newkey.master, err = newkey.newKeys() if err != nil { return nil, err } } 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) scrypt(password string) (*keys, error) { if len(k.Salt) == 0 { return nil, fmt.Errorf("scrypt() called with empty salt") } keybytes := hmacKeysize + aesKeysize scryptKeys, err := scrypt.Key([]byte(password), k.Salt, k.N, k.R, k.P, keybytes) if err != nil { return nil, fmt.Errorf("error deriving keys from password: %v", err) } if len(scryptKeys) != keybytes { return nil, fmt.Errorf("invalid numbers of bytes expanded from scrypt(): %d", len(scryptKeys)) } ks := &keys{ Encrypt: scryptKeys[:aesKeysize], Sign: scryptKeys[aesKeysize:], } return ks, nil } func (k *Key) newKeys() (*keys, error) { ks := &keys{ Encrypt: make([]byte, aesKeysize), Sign: make([]byte, hmacKeysize), } n, err := rand.Read(ks.Encrypt) if n != aesKeysize || err != nil { panic("unable to read enough random bytes for encryption key") } n, err = rand.Read(ks.Sign) if n != hmacKeysize || err != nil { panic("unable to read enough random bytes for signing key") } return ks, 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 } // Encrypt encrypts and signs data. Stored in ciphertext is IV || Ciphertext || // HMAC. Encrypt returns the ciphertext's length. For the hash function, SHA256 // is used, so the overhead is 16+32=48 byte. func (k *Key) encrypt(ks *keys, ciphertext, plaintext []byte) (int, error) { if cap(ciphertext) < len(plaintext)+ivSize+hmacSize { return 0, ErrBufferTooSmall } _, err := io.ReadFull(rand.Reader, ciphertext[:ivSize]) if err != nil { panic(fmt.Sprintf("unable to generate new random iv: %v", err)) } c, err := aes.NewCipher(ks.Encrypt) if err != nil { panic(fmt.Sprintf("unable to create cipher: %v", err)) } e := cipher.NewCTR(c, ciphertext[:ivSize]) e.XORKeyStream(ciphertext[ivSize:cap(ciphertext)], plaintext) ciphertext = ciphertext[:ivSize+len(plaintext)] hm := hmac.New(sha256.New, ks.Sign) n, err := hm.Write(ciphertext) if err != nil || n != len(ciphertext) { panic(fmt.Sprintf("unable to calculate hmac of ciphertext: %v", err)) } ciphertext = hm.Sum(ciphertext) return len(ciphertext), nil } // EncryptUser encrypts and signs data with the user key. Stored in ciphertext // is IV || Ciphertext || HMAC. Returns the ciphertext length. For the hash // function, SHA256 is used, so the overhead is 16+32=48 byte. func (k *Key) EncryptUser(ciphertext, plaintext []byte) (int, error) { return k.encrypt(k.user, ciphertext, plaintext) } // Encrypt encrypts and signs data with the master key. Stored in ciphertext is // IV || Ciphertext || HMAC. Returns the ciphertext length. For the hash // function, SHA256 is used, so the overhead is 16+32=48 byte. func (k *Key) Encrypt(ciphertext, plaintext []byte) (int, error) { return k.encrypt(k.master, ciphertext, plaintext) } type encryptWriter struct { iv []byte wroteIV bool h hash.Hash s cipher.Stream w io.Writer origWr io.Writer err error // remember error writing iv } func (e *encryptWriter) Close() error { // write hmac _, err := e.origWr.Write(e.h.Sum(nil)) if err != nil { return err } return nil } const encryptWriterChunkSize = 512 * 1024 // 512 KiB var encryptWriterBufPool = sync.Pool{ New: func() interface{} { return make([]byte, encryptWriterChunkSize) }, } func (e *encryptWriter) Write(p []byte) (int, error) { // write iv first if !e.wroteIV { _, e.err = e.origWr.Write(e.iv) e.wroteIV = true } if e.err != nil { return 0, e.err } buf := encryptWriterBufPool.Get().([]byte) defer encryptWriterBufPool.Put(buf) written := 0 for len(p) > 0 { max := len(p) if max > encryptWriterChunkSize { max = encryptWriterChunkSize } e.s.XORKeyStream(buf, p[:max]) n, err := e.w.Write(buf[:max]) if n != max { if err == nil { // should never happen err = io.ErrShortWrite } } written += n p = p[n:] if err != nil { e.err = err return written, err } } return written, nil } func (k *Key) encryptTo(ks *keys, wr io.Writer) io.WriteCloser { ew := &encryptWriter{ iv: make([]byte, ivSize), h: hmac.New(sha256.New, ks.Sign), origWr: wr, } _, err := io.ReadFull(rand.Reader, ew.iv) if err != nil { panic(fmt.Sprintf("unable to generate new random iv: %v", err)) } // write iv to hmac _, err = ew.h.Write(ew.iv) if err != nil { panic(err) } c, err := aes.NewCipher(ks.Encrypt) if err != nil { panic(fmt.Sprintf("unable to create cipher: %v", err)) } ew.s = cipher.NewCTR(c, ew.iv) ew.w = io.MultiWriter(ew.h, wr) return ew } // 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 k.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 k.encryptTo(k.user, wr) } // Decrypt verifes and decrypts the ciphertext. Ciphertext must be in the form // IV || Ciphertext || HMAC. func (k *Key) decrypt(ks *keys, plaintext, ciphertext []byte) ([]byte, error) { // check for plausible length if len(ciphertext) < ivSize+hmacSize { panic("trying to decrypt invalid data: ciphertext too small") } if cap(plaintext) < len(ciphertext) { // extend plaintext plaintext = append(plaintext, make([]byte, len(ciphertext)-cap(plaintext))...) } hm := hmac.New(sha256.New, ks.Sign) // extract hmac l := len(ciphertext) - hm.Size() ciphertext, mac := ciphertext[:l], ciphertext[l:] // calculate new hmac n, err := hm.Write(ciphertext) if err != nil || n != len(ciphertext) { panic(fmt.Sprintf("unable to calculate hmac of ciphertext, err %v", err)) } // verify hmac mac2 := hm.Sum(nil) if !hmac.Equal(mac, mac2) { return nil, ErrUnauthenticated } // extract iv iv, ciphertext := ciphertext[:aes.BlockSize], ciphertext[aes.BlockSize:] // decrypt data c, err := aes.NewCipher(ks.Encrypt) if err != nil { panic(fmt.Sprintf("unable to create cipher: %v", err)) } // decrypt e := cipher.NewCTR(c, iv) e.XORKeyStream(plaintext, ciphertext) plaintext = plaintext[:len(ciphertext)] return plaintext, nil } // Decrypt verifes and decrypts the ciphertext with the master key. Ciphertext // must be in the form IV || Ciphertext || HMAC. func (k *Key) Decrypt(plaintext, ciphertext []byte) ([]byte, error) { return k.decrypt(k.master, plaintext, ciphertext) } // DecryptUser verifes and decrypts the ciphertext with the user key. Ciphertext // must be in the form IV || Ciphertext || HMAC. func (k *Key) DecryptUser(plaintext, ciphertext []byte) ([]byte, error) { return k.decrypt(k.user, plaintext, ciphertext) } type decryptReader struct { buf []byte pos int } func (d *decryptReader) Read(dst []byte) (int, error) { if d.buf == nil { return 0, io.EOF } if len(dst) == 0 { return 0, nil } remaining := len(d.buf) - d.pos if len(dst) >= remaining { n := copy(dst, d.buf[d.pos:]) d.Close() return n, io.EOF } n := copy(dst, d.buf[d.pos:d.pos+len(dst)]) d.pos += n return n, nil } func (d *decryptReader) Close() error { if d.buf == nil { return nil } FreeChunkBuf("decryptReader", d.buf) d.buf = nil return nil } // decryptFrom verifies and decrypts the ciphertext read from rd with ks and // makes it available on the returned Reader. Ciphertext must be in the form IV // || Ciphertext || HMAC. In order to correctly verify the ciphertext, rd is // drained, locally buffered and made available on the returned Reader // afterwards. If an HMAC verification failure is observed, it is returned // immediately. func (k *Key) decryptFrom(ks *keys, rd io.Reader) (io.ReadCloser, error) { ciphertext := GetChunkBuf("decryptReader") ciphertext = ciphertext[0:cap(ciphertext)] n, err := io.ReadFull(rd, ciphertext) if err != io.ErrUnexpectedEOF { // read remaining data buf, e := ioutil.ReadAll(rd) ciphertext = append(ciphertext, buf...) n += len(buf) err = e } else { err = nil } if err != nil { return nil, err } ciphertext = ciphertext[:n] // check for plausible length if len(ciphertext) < ivSize+hmacSize { panic("trying to decrypt invalid data: ciphertext too small") } hm := hmac.New(sha256.New, ks.Sign) // extract hmac l := len(ciphertext) - hm.Size() ciphertext, mac := ciphertext[:l], ciphertext[l:] // calculate new hmac n, err = hm.Write(ciphertext) if err != nil || n != len(ciphertext) { panic(fmt.Sprintf("unable to calculate hmac of ciphertext, err %v", err)) } // verify hmac mac2 := hm.Sum(nil) if !hmac.Equal(mac, mac2) { return nil, ErrUnauthenticated } // extract iv iv, ciphertext := ciphertext[:aes.BlockSize], ciphertext[aes.BlockSize:] // decrypt data c, err := aes.NewCipher(ks.Encrypt) if err != nil { panic(fmt.Sprintf("unable to create cipher: %v", err)) } stream := cipher.NewCTR(c, iv) stream.XORKeyStream(ciphertext, ciphertext) return &decryptReader{buf: ciphertext}, nil } // 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 || HMAC. In order to correctly verify the ciphertext, rd is // drained, locally buffered and made available on the returned Reader // afterwards. If an HMAC verification failure is observed, it is returned // immediately. func (k *Key) DecryptFrom(rd io.Reader) (io.ReadCloser, error) { return k.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 || HMAC. In order to correctly verify the ciphertext, // rd is drained, locally buffered and made available on the returned Reader // afterwards. If an HMAC verification failure is observed, it is returned // immediately. func (k *Key) DecryptUserFrom(rd io.Reader) (io.ReadCloser, error) { return k.decryptFrom(k.user, rd) } 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 }