From 420030998fdb74f155aa03156f6ce7524120e4bd Mon Sep 17 00:00:00 2001
From: Zack Scholl <zack.scholl@gmail.com>
Date: Wed, 21 Apr 2021 16:53:29 -0700
Subject: [PATCH] add chacha20

---
 src/crypt/crypt.go      | 61 +++++++++++++++++++++++++++++++++++++++++
 src/crypt/crypt_test.go | 50 +++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+)

diff --git a/src/crypt/crypt.go b/src/crypt/crypt.go
index 3991e567..d33a4d8c 100644
--- a/src/crypt/crypt.go
+++ b/src/crypt/crypt.go
@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"log"
 
+	"golang.org/x/crypto/argon2"
+	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/crypto/pbkdf2"
 )
 
@@ -70,3 +72,62 @@ func Decrypt(encrypted []byte, key []byte) (plaintext []byte, err error) {
 	plaintext, err = aesgcm.Open(nil, encrypted[:12], encrypted[12:], nil)
 	return
 }
+
+// NewArgon2 generates a new key based on a passphrase and salt
+// using argon2
+// https://pkg.go.dev/golang.org/x/crypto/argon2
+func NewArgon2(passphrase []byte, usersalt []byte) (key []byte, salt []byte, err error) {
+	if len(passphrase) < 1 {
+		err = fmt.Errorf("need more than that for passphrase")
+		return
+	}
+	if usersalt == nil {
+		salt = make([]byte, 8)
+		// http://www.ietf.org/rfc/rfc2898.txt
+		// Salt.
+		if _, err := rand.Read(salt); err != nil {
+			log.Fatalf("can't get random salt: %v", err)
+		}
+	} else {
+		salt = usersalt
+	}
+	key = argon2.IDKey(passphrase, salt, 1, 64*1024, 4, 32)
+	return
+}
+
+// EncryptChaCha will encrypt ChaCha20-Poly1305 using the pre-generated key
+// https://pkg.go.dev/golang.org/x/crypto/chacha20poly1305
+func EncryptChaCha(plaintext []byte, key []byte) (encrypted []byte, err error) {
+	aead, err := chacha20poly1305.NewX(key)
+	if err != nil {
+		return
+	}
+	nonce := make([]byte, aead.NonceSize(), aead.NonceSize()+len(plaintext)+aead.Overhead())
+	if _, err := rand.Read(nonce); err != nil {
+		panic(err)
+	}
+
+	// Encrypt the message and append the ciphertext to the nonce.
+	encrypted = aead.Seal(nonce, nonce, plaintext, nil)
+	return
+}
+
+// DecryptChaCha will encrypt ChaCha20-Poly1305 using the pre-generated key
+// https://pkg.go.dev/golang.org/x/crypto/chacha20poly1305
+func DecryptChaCha(encryptedMsg []byte, key []byte) (encrypted []byte, err error) {
+	aead, err := chacha20poly1305.NewX(key)
+	if err != nil {
+		return
+	}
+	if len(encryptedMsg) < aead.NonceSize() {
+		err = fmt.Errorf("ciphertext too short")
+		return
+	}
+
+	// Split nonce and ciphertext.
+	nonce, ciphertext := encryptedMsg[:aead.NonceSize()], encryptedMsg[aead.NonceSize():]
+
+	// Decrypt the message and check it wasn't tampered with.
+	encrypted, err = aead.Open(nil, nonce, ciphertext, nil)
+	return
+}
diff --git a/src/crypt/crypt_test.go b/src/crypt/crypt_test.go
index 54331682..d47dd4c4 100644
--- a/src/crypt/crypt_test.go
+++ b/src/crypt/crypt_test.go
@@ -1,6 +1,7 @@
 package crypt
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -23,6 +24,23 @@ func BenchmarkDecrypt(b *testing.B) {
 	}
 }
 
+func BenchmarkEncryptChaCha(b *testing.B) {
+	bob, _, _ := NewArgon2([]byte("password"), nil)
+	for i := 0; i < b.N; i++ {
+		EncryptChaCha([]byte("hello, world"), bob)
+	}
+}
+
+func BenchmarkDecryptChaCha(b *testing.B) {
+	key, _, _ := NewArgon2([]byte("password"), nil)
+	msg := []byte("hello, world")
+	enc, _ := EncryptChaCha(msg, key)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		DecryptChaCha(enc, key)
+	}
+}
+
 func TestEncryption(t *testing.T) {
 	key, salt, err := New([]byte("password"), nil)
 	assert.Nil(t, err)
@@ -53,3 +71,35 @@ func TestEncryption(t *testing.T) {
 	_, _, err = New([]byte(""), nil)
 	assert.NotNil(t, err)
 }
+
+func TestEncryptionChaCha(t *testing.T) {
+	key, salt, err := NewArgon2([]byte("password"), nil)
+	fmt.Printf("key: %x\n", key)
+	assert.Nil(t, err)
+	msg := []byte("hello, world")
+	enc, err := EncryptChaCha(msg, key)
+	assert.Nil(t, err)
+	dec, err := DecryptChaCha(enc, key)
+	assert.Nil(t, err)
+	assert.Equal(t, msg, dec)
+
+	// check reusing the salt
+	key2, _, err := NewArgon2([]byte("password"), salt)
+	dec, err = DecryptChaCha(enc, key2)
+	assert.Nil(t, err)
+	assert.Equal(t, msg, dec)
+
+	// check reusing the salt
+	key2, _, err = NewArgon2([]byte("wrong password"), salt)
+	dec, err = DecryptChaCha(enc, key2)
+	assert.NotNil(t, err)
+	assert.NotEqual(t, msg, dec)
+
+	// error with no password
+	dec, err = DecryptChaCha([]byte(""), key)
+	assert.NotNil(t, err)
+
+	// error with small password
+	_, _, err = NewArgon2([]byte(""), nil)
+	assert.NotNil(t, err)
+}