From 181aa56c8711c9dc40eb7d2f2b259b0d1ed5240e Mon Sep 17 00:00:00 2001
From: Jae Kwon <jae@tendermint.com>
Date: Sun, 13 Mar 2016 12:55:02 -0700
Subject: [PATCH] Added symmetric encrypt/decrypt methods

---
 encrypt.go      | 51 +++++++++++++++++++++++++++++++++++++++++++++++++
 encrypt_test.go | 51 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 encrypt.go
 create mode 100644 encrypt_test.go

diff --git a/encrypt.go b/encrypt.go
new file mode 100644
index 000000000..36bddd44c
--- /dev/null
+++ b/encrypt.go
@@ -0,0 +1,51 @@
+package crypto
+
+import (
+	"errors"
+
+	. "github.com/tendermint/go-common"
+	"golang.org/x/crypto/nacl/secretbox"
+)
+
+const nonceLen = 24
+const secretLen = 32
+
+// secret must be 32 bytes long. Use something like Sha256(Bcrypt(passphrase))
+// The ciphertext is (secretbox.Overhead + 24) bytes longer than the plaintext.
+// NOTE: call crypto.MixEntropy() first.
+func EncryptSymmetric(plaintext []byte, secret []byte) (ciphertext []byte) {
+	if len(secret) != secretLen {
+		PanicSanity(Fmt("Secret must be 32 bytes long, got len %v", len(secret)))
+	}
+	nonce := CRandBytes(nonceLen)
+	nonceArr := [nonceLen]byte{}
+	copy(nonceArr[:], nonce)
+	secretArr := [secretLen]byte{}
+	copy(secretArr[:], secret)
+	ciphertext = make([]byte, nonceLen+secretbox.Overhead+len(plaintext))
+	copy(ciphertext, nonce)
+	secretbox.Seal(ciphertext[nonceLen:nonceLen], plaintext, &nonceArr, &secretArr)
+	return ciphertext
+}
+
+// secret must be 32 bytes long. Use something like Sha256(Bcrypt(passphrase))
+// The ciphertext is (secretbox.Overhead + 24) bytes longer than the plaintext.
+func DecryptSymmetric(ciphertext []byte, secret []byte) (plaintext []byte, err error) {
+	if len(secret) != secretLen {
+		PanicSanity(Fmt("Secret must be 32 bytes long, got len %v", len(secret)))
+	}
+	if len(ciphertext) <= secretbox.Overhead+nonceLen {
+		return nil, errors.New("Ciphertext is too short")
+	}
+	nonce := ciphertext[:nonceLen]
+	nonceArr := [nonceLen]byte{}
+	copy(nonceArr[:], nonce)
+	secretArr := [secretLen]byte{}
+	copy(secretArr[:], secret)
+	plaintext = make([]byte, len(ciphertext)-nonceLen-secretbox.Overhead)
+	_, ok := secretbox.Open(plaintext[:0], ciphertext[nonceLen:], &nonceArr, &secretArr)
+	if !ok {
+		return nil, errors.New("Ciphertext decryption failed")
+	}
+	return plaintext, nil
+}
diff --git a/encrypt_test.go b/encrypt_test.go
new file mode 100644
index 000000000..f05c812b6
--- /dev/null
+++ b/encrypt_test.go
@@ -0,0 +1,51 @@
+package crypto
+
+import (
+	"bytes"
+	"golang.org/x/crypto/bcrypt"
+	"testing"
+)
+
+func TestSimple(t *testing.T) {
+
+	MixEntropy([]byte("someentropy"))
+
+	plaintext := []byte("sometext")
+	secret := []byte("somesecretoflengththirtytwo===32")
+	ciphertext := EncryptSymmetric(plaintext, secret)
+
+	plaintext2, err := DecryptSymmetric(ciphertext, secret)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(plaintext, plaintext2) {
+		t.Errorf("Decrypted plaintext was %X, expected %X", plaintext2, plaintext)
+	}
+
+}
+
+func TestSimpleWithKDF(t *testing.T) {
+
+	MixEntropy([]byte("someentropy"))
+
+	plaintext := []byte("sometext")
+	secretPass := []byte("somesecret")
+	secret, err := bcrypt.GenerateFromPassword(secretPass, 12)
+	if err != nil {
+		t.Error(err)
+	}
+	secret = Sha256(secret)
+
+	ciphertext := EncryptSymmetric(plaintext, secret)
+
+	plaintext2, err := DecryptSymmetric(ciphertext, secret)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !bytes.Equal(plaintext, plaintext2) {
+		t.Errorf("Decrypted plaintext was %X, expected %X", plaintext2, plaintext)
+	}
+
+}