Revert "Don't use modules"

This reverts commit bffe99aeadae09abd02f2bd3184925af6b680535.

2 files changed, 265 insertions, 0 deletions

diff --git a/internal/xchacha20poly1305/xchacha20.go b/internal/xchacha20poly1305/xchacha20.go
new file mode 100644
index 0000000..a6e59f0
--- /dev/null
+++ b/internal/xchacha20poly1305/xchacha20.go
@@ -0,0 +1,169 @@
+// Copyright (c) 2016 Andreas Auernhammer. All rights reserved.
+// Use of this source code is governed by a license that can be
+// found in the LICENSE file.
+
+package xchacha20poly1305
+
+import (
+	"encoding/binary"
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+func hChaCha20(out *[32]byte, nonce []byte, key *[32]byte) {
+
+	v00 := uint32(0x61707865)
+	v01 := uint32(0x3320646e)
+	v02 := uint32(0x79622d32)
+	v03 := uint32(0x6b206574)
+
+	v04 := binary.LittleEndian.Uint32(key[0:])
+	v05 := binary.LittleEndian.Uint32(key[4:])
+	v06 := binary.LittleEndian.Uint32(key[8:])
+	v07 := binary.LittleEndian.Uint32(key[12:])
+	v08 := binary.LittleEndian.Uint32(key[16:])
+	v09 := binary.LittleEndian.Uint32(key[20:])
+	v10 := binary.LittleEndian.Uint32(key[24:])
+	v11 := binary.LittleEndian.Uint32(key[28:])
+	v12 := binary.LittleEndian.Uint32(nonce[0:])
+	v13 := binary.LittleEndian.Uint32(nonce[4:])
+	v14 := binary.LittleEndian.Uint32(nonce[8:])
+	v15 := binary.LittleEndian.Uint32(nonce[12:])
+
+	for i := 0; i < 20; i += 2 {
+		v00 += v04
+		v12 ^= v00
+		v12 = (v12 << 16) | (v12 >> 16)
+		v08 += v12
+		v04 ^= v08
+		v04 = (v04 << 12) | (v04 >> 20)
+		v00 += v04
+		v12 ^= v00
+		v12 = (v12 << 8) | (v12 >> 24)
+		v08 += v12
+		v04 ^= v08
+		v04 = (v04 << 7) | (v04 >> 25)
+		v01 += v05
+		v13 ^= v01
+		v13 = (v13 << 16) | (v13 >> 16)
+		v09 += v13
+		v05 ^= v09
+		v05 = (v05 << 12) | (v05 >> 20)
+		v01 += v05
+		v13 ^= v01
+		v13 = (v13 << 8) | (v13 >> 24)
+		v09 += v13
+		v05 ^= v09
+		v05 = (v05 << 7) | (v05 >> 25)
+		v02 += v06
+		v14 ^= v02
+		v14 = (v14 << 16) | (v14 >> 16)
+		v10 += v14
+		v06 ^= v10
+		v06 = (v06 << 12) | (v06 >> 20)
+		v02 += v06
+		v14 ^= v02
+		v14 = (v14 << 8) | (v14 >> 24)
+		v10 += v14
+		v06 ^= v10
+		v06 = (v06 << 7) | (v06 >> 25)
+		v03 += v07
+		v15 ^= v03
+		v15 = (v15 << 16) | (v15 >> 16)
+		v11 += v15
+		v07 ^= v11
+		v07 = (v07 << 12) | (v07 >> 20)
+		v03 += v07
+		v15 ^= v03
+		v15 = (v15 << 8) | (v15 >> 24)
+		v11 += v15
+		v07 ^= v11
+		v07 = (v07 << 7) | (v07 >> 25)
+		v00 += v05
+		v15 ^= v00
+		v15 = (v15 << 16) | (v15 >> 16)
+		v10 += v15
+		v05 ^= v10
+		v05 = (v05 << 12) | (v05 >> 20)
+		v00 += v05
+		v15 ^= v00
+		v15 = (v15 << 8) | (v15 >> 24)
+		v10 += v15
+		v05 ^= v10
+		v05 = (v05 << 7) | (v05 >> 25)
+		v01 += v06
+		v12 ^= v01
+		v12 = (v12 << 16) | (v12 >> 16)
+		v11 += v12
+		v06 ^= v11
+		v06 = (v06 << 12) | (v06 >> 20)
+		v01 += v06
+		v12 ^= v01
+		v12 = (v12 << 8) | (v12 >> 24)
+		v11 += v12
+		v06 ^= v11
+		v06 = (v06 << 7) | (v06 >> 25)
+		v02 += v07
+		v13 ^= v02
+		v13 = (v13 << 16) | (v13 >> 16)
+		v08 += v13
+		v07 ^= v08
+		v07 = (v07 << 12) | (v07 >> 20)
+		v02 += v07
+		v13 ^= v02
+		v13 = (v13 << 8) | (v13 >> 24)
+		v08 += v13
+		v07 ^= v08
+		v07 = (v07 << 7) | (v07 >> 25)
+		v03 += v04
+		v14 ^= v03
+		v14 = (v14 << 16) | (v14 >> 16)
+		v09 += v14
+		v04 ^= v09
+		v04 = (v04 << 12) | (v04 >> 20)
+		v03 += v04
+		v14 ^= v03
+		v14 = (v14 << 8) | (v14 >> 24)
+		v09 += v14
+		v04 ^= v09
+		v04 = (v04 << 7) | (v04 >> 25)
+	}
+
+	binary.LittleEndian.PutUint32(out[0:], v00)
+	binary.LittleEndian.PutUint32(out[4:], v01)
+	binary.LittleEndian.PutUint32(out[8:], v02)
+	binary.LittleEndian.PutUint32(out[12:], v03)
+	binary.LittleEndian.PutUint32(out[16:], v12)
+	binary.LittleEndian.PutUint32(out[20:], v13)
+	binary.LittleEndian.PutUint32(out[24:], v14)
+	binary.LittleEndian.PutUint32(out[28:], v15)
+}
+
+func Encrypt(
+	dst []byte,
+	nonceFull *[24]byte,
+	plaintext []byte,
+	additionalData []byte,
+	key *[chacha20poly1305.KeySize]byte,
+) []byte {
+	var nonce [chacha20poly1305.NonceSize]byte
+	var derivedKey [chacha20poly1305.KeySize]byte
+	hChaCha20(&derivedKey, nonceFull[:16], key)
+	aead, _ := chacha20poly1305.New(derivedKey[:])
+	copy(nonce[4:], nonceFull[16:])
+	return aead.Seal(dst, nonce[:], plaintext, additionalData)
+}
+
+func Decrypt(
+	dst []byte,
+	nonceFull *[24]byte,
+	plaintext []byte,
+	additionalData []byte,
+	key *[chacha20poly1305.KeySize]byte,
+) ([]byte, error) {
+	var nonce [chacha20poly1305.NonceSize]byte
+	var derivedKey [chacha20poly1305.KeySize]byte
+	hChaCha20(&derivedKey, nonceFull[:16], key)
+	aead, _ := chacha20poly1305.New(derivedKey[:])
+	copy(nonce[4:], nonceFull[16:])
+	return aead.Open(dst, nonce[:], plaintext, additionalData)
+}
diff --git a/internal/xchacha20poly1305/xchacha20_test.go b/internal/xchacha20poly1305/xchacha20_test.go
new file mode 100644
index 0000000..5d5b78f
--- /dev/null
+++ b/internal/xchacha20poly1305/xchacha20_test.go
@@ -0,0 +1,96 @@
+package xchacha20poly1305
+
+import (
+	"encoding/hex"
+	"testing"
+)
+
+type XChaCha20Test struct {
+	Nonce string
+	Key   string
+	PT    string
+	CT    string
+}
+
+func TestXChaCha20(t *testing.T) {
+
+	tests := []XChaCha20Test{
+		{
+			Nonce: "000000000000000000000000000000000000000000000000",
+			Key:   "0000000000000000000000000000000000000000000000000000000000000000",
+			PT:    "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
+			CT:    "789e9689e5208d7fd9e1f3c5b5341f48ef18a13e418998addadd97a3693a987f8e82ecd5c1433bfed1af49750c0f1ff29c4174a05b119aa3a9e8333812e0c0feb1299c5949d895ee01dbf50f8395dd84",
+		},
+		{
+			Nonce: "0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f",
+			Key:   "0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f",
+			PT:    "0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f",
+			CT:    "e1a046aa7f71e2af8b80b6408b2fd8d3a350278cde79c94d9efaa475e1339b3dd490127b",
+		},
+		{
+			Nonce: "d9a8213e8a697508805c2c171ad54487ead9e3e02d82d5bc",
+			Key:   "979196dbd78526f2f584f7534db3f5824d8ccfa858ca7e09bdd3656ecd36033c",
+			PT:    "43cc6d624e451bbed952c3e071dc6c03392ce11eb14316a94b2fdc98b22fedea",
+			CT:    "53c1e8bef2dbb8f2505ec010a7afe21d5a8e6dd8f987e4ea1a2ed5dfbc844ea400db34496fd2153526c6e87c36694200",
+		},
+	}
+
+	for _, test := range tests {
+
+		nonce, err := hex.DecodeString(test.Nonce)
+		if err != nil {
+			panic(err)
+		}
+
+		key, err := hex.DecodeString(test.Key)
+		if err != nil {
+			panic(err)
+		}
+
+		pt, err := hex.DecodeString(test.PT)
+		if err != nil {
+			panic(err)
+		}
+
+		func() {
+			var nonceArray [24]byte
+			var keyArray [32]byte
+			copy(nonceArray[:], nonce)
+			copy(keyArray[:], key)
+
+			// test encryption
+
+			ct := Encrypt(
+				nil,
+				&nonceArray,
+				pt,
+				nil,
+				&keyArray,
+			)
+			ctHex := hex.EncodeToString(ct)
+			if ctHex != test.CT {
+				t.Fatal("encryption failed, expected:", test.CT, "got", ctHex)
+			}
+
+			// test decryption
+
+			ptp, err := Decrypt(
+				nil,
+				&nonceArray,
+				ct,
+				nil,
+				&keyArray,
+			)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			ptHex := hex.EncodeToString(ptp)
+			if ptHex != test.PT {
+				t.Fatal("decryption failed, expected:", test.PT, "got", ptHex)
+			}
+		}()
+
+	}
+
+}