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// Package encrypted provides a simple, secure system for encrypting data
// symmetrically with a passphrase.
//
// It uses scrypt derive a key from the passphrase and the NaCl secret box
// cipher for authenticated encryption.
package encrypted
import (
"crypto/rand"
"encoding/json"
"errors"
"fmt"
"io"
"golang.org/x/crypto/nacl/secretbox"
"golang.org/x/crypto/scrypt"
)
const saltSize = 32
const (
boxKeySize = 32
boxNonceSize = 24
)
const (
// N parameter was chosen to be ~100ms of work using the default implementation
// on the 2.3GHz Core i7 Haswell processor in a late-2013 Apple Retina Macbook
// Pro (it takes ~113ms).
scryptN = 32768
scryptR = 8
scryptP = 1
)
const (
nameScrypt = "scrypt"
nameSecretBox = "nacl/secretbox"
)
type data struct {
KDF scryptKDF `json:"kdf"`
Cipher secretBoxCipher `json:"cipher"`
Ciphertext []byte `json:"ciphertext"`
}
type scryptParams struct {
N int `json:"N"`
R int `json:"r"`
P int `json:"p"`
}
func newScryptKDF() (scryptKDF, error) {
salt := make([]byte, saltSize)
if err := fillRandom(salt); err != nil {
return scryptKDF{}, err
}
return scryptKDF{
Name: nameScrypt,
Params: scryptParams{
N: scryptN,
R: scryptR,
P: scryptP,
},
Salt: salt,
}, nil
}
type scryptKDF struct {
Name string `json:"name"`
Params scryptParams `json:"params"`
Salt []byte `json:"salt"`
}
func (s *scryptKDF) Key(passphrase []byte) ([]byte, error) {
return scrypt.Key(passphrase, s.Salt, s.Params.N, s.Params.R, s.Params.P, boxKeySize)
}
// CheckParams checks that the encoded KDF parameters are what we expect them to
// be. If we do not do this, an attacker could cause a DoS by tampering with
// them.
func (s *scryptKDF) CheckParams() error {
if s.Params.N != scryptN || s.Params.R != scryptR || s.Params.P != scryptP {
return errors.New("encrypted: unexpected kdf parameters")
}
return nil
}
func newSecretBoxCipher() (secretBoxCipher, error) {
nonce := make([]byte, boxNonceSize)
if err := fillRandom(nonce); err != nil {
return secretBoxCipher{}, err
}
return secretBoxCipher{
Name: nameSecretBox,
Nonce: nonce,
}, nil
}
type secretBoxCipher struct {
Name string `json:"name"`
Nonce []byte `json:"nonce"`
encrypted bool
}
func (s *secretBoxCipher) Encrypt(plaintext, key []byte) []byte {
var keyBytes [boxKeySize]byte
var nonceBytes [boxNonceSize]byte
if len(key) != len(keyBytes) {
panic("incorrect key size")
}
if len(s.Nonce) != len(nonceBytes) {
panic("incorrect nonce size")
}
copy(keyBytes[:], key)
copy(nonceBytes[:], s.Nonce)
// ensure that we don't re-use nonces
if s.encrypted {
panic("Encrypt must only be called once for each cipher instance")
}
s.encrypted = true
return secretbox.Seal(nil, plaintext, &nonceBytes, &keyBytes)
}
func (s *secretBoxCipher) Decrypt(ciphertext, key []byte) ([]byte, error) {
var keyBytes [boxKeySize]byte
var nonceBytes [boxNonceSize]byte
if len(key) != len(keyBytes) {
panic("incorrect key size")
}
if len(s.Nonce) != len(nonceBytes) {
// return an error instead of panicking since the nonce is user input
return nil, errors.New("encrypted: incorrect nonce size")
}
copy(keyBytes[:], key)
copy(nonceBytes[:], s.Nonce)
res, ok := secretbox.Open(nil, ciphertext, &nonceBytes, &keyBytes)
if !ok {
return nil, errors.New("encrypted: decryption failed")
}
return res, nil
}
// Encrypt takes a passphrase and plaintext, and returns a JSON object
// containing ciphertext and the details necessary to decrypt it.
func Encrypt(plaintext, passphrase []byte) ([]byte, error) {
k, err := newScryptKDF()
if err != nil {
return nil, err
}
key, err := k.Key(passphrase)
if err != nil {
return nil, err
}
c, err := newSecretBoxCipher()
if err != nil {
return nil, err
}
data := &data{
KDF: k,
Cipher: c,
}
data.Ciphertext = c.Encrypt(plaintext, key)
return json.Marshal(data)
}
// Marshal encrypts the JSON encoding of v using passphrase.
func Marshal(v interface{}, passphrase []byte) ([]byte, error) {
data, err := json.MarshalIndent(v, "", "\t")
if err != nil {
return nil, err
}
return Encrypt(data, passphrase)
}
// Decrypt takes a JSON-encoded ciphertext object encrypted using Encrypt and
// tries to decrypt it using passphrase. If successful, it returns the
// plaintext.
func Decrypt(ciphertext, passphrase []byte) ([]byte, error) {
data := &data{}
if err := json.Unmarshal(ciphertext, data); err != nil {
return nil, err
}
if data.KDF.Name != nameScrypt {
return nil, fmt.Errorf("encrypted: unknown kdf name %q", data.KDF.Name)
}
if data.Cipher.Name != nameSecretBox {
return nil, fmt.Errorf("encrypted: unknown cipher name %q", data.Cipher.Name)
}
if err := data.KDF.CheckParams(); err != nil {
return nil, err
}
key, err := data.KDF.Key(passphrase)
if err != nil {
return nil, err
}
return data.Cipher.Decrypt(data.Ciphertext, key)
}
// Unmarshal decrypts the data using passphrase and unmarshals the resulting
// plaintext into the value pointed to by v.
func Unmarshal(data []byte, v interface{}, passphrase []byte) error {
decrypted, err := Decrypt(data, passphrase)
if err != nil {
return err
}
return json.Unmarshal(decrypted, v)
}
func fillRandom(b []byte) error {
_, err := io.ReadFull(rand.Reader, b)
return err
}
|
