From 1d8c818ec4f1c18e1334e31c3805888c4185d185 Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Tue, 22 Aug 2023 23:45:37 +0000
Subject: [PATCH] wireguard: make PrivateKey and PublicKey two distinct types

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 pkg/wireguard/config.go |  8 ++--
 pkg/wireguard/keys.go   | 90 ++++++++++++++++++++++++++++++++++-------
 2 files changed, 79 insertions(+), 19 deletions(-)

diff --git a/pkg/wireguard/config.go b/pkg/wireguard/config.go
index ab22c69..931e37b 100644
--- a/pkg/wireguard/config.go
+++ b/pkg/wireguard/config.go
@@ -31,13 +31,13 @@ func (f *Config) Peers() int {
 // InterfaceConfig represents the [Interface] section
 type InterfaceConfig struct {
 	Address    netip.Addr
-	PrivateKey BinaryKey
+	PrivateKey PrivateKey
 	ListenPort uint16
 }
 
 // PeerConfig represents a [Peer] section
 type PeerConfig struct {
-	PublicKey  BinaryKey
+	PublicKey  PublicKey
 	Endpoint   EndpointAddress
 	AllowedIPs []netip.Prefix
 }
@@ -135,7 +135,7 @@ func (p interfaceConfig) Export() (InterfaceConfig, error) {
 		ListenPort: p.ListenPort,
 	}
 
-	out.PrivateKey, err = BinaryKeyFromBase64(p.PrivateKey)
+	out.PrivateKey, err = PrivateKeyFromBase64(p.PrivateKey)
 	if err != nil {
 		err = core.Wrap(err, "PrivateKey")
 		return InterfaceConfig{}, err
@@ -162,7 +162,7 @@ func (v *intermediateConfig) ExportPeer(i int) (PeerConfig, error) {
 	}
 
 	// PublicKey
-	out.PublicKey, err = BinaryKeyFromBase64(v.Peer.PublicKey[i])
+	out.PublicKey, err = PublicKeyFromBase64(v.Peer.PublicKey[i])
 	if err != nil {
 		err = core.Wrap(err, "PublicKey")
 		return out, err
diff --git a/pkg/wireguard/keys.go b/pkg/wireguard/keys.go
index 12bf58e..c6acea0 100644
--- a/pkg/wireguard/keys.go
+++ b/pkg/wireguard/keys.go
@@ -3,34 +3,94 @@ package wireguard
 import (
 	"bytes"
 	"encoding/base64"
+	"errors"
 )
 
-// BinaryKey is a binary blob
-type BinaryKey []byte
+const (
+	// PrivateKeySize is the length in bytes of a Wireguard Private Key
+	PrivateKeySize = 32
+	// PublicKeySize is the length in bytes of a Wireguard Public Key
+	PublicKeySize = 32
+)
+
+var (
+	// ErrInvalidKeySize indicates the key size is wrong
+	ErrInvalidKeySize = errors.New("invalid key size")
+)
+
+type (
+	// PrivateKey is a binary Wireguard Private Key
+	PrivateKey []byte
+	// PublicKey is a binary Wireguard Public Key
+	PublicKey []byte
+)
+
+func (key PrivateKey) String() string {
+	return encodeKey(key)
+}
+
+func (pub PublicKey) String() string {
+	return encodeKey(pub)
+}
 
-func (k BinaryKey) String() string {
-	return base64.StdEncoding.EncodeToString(k)
+// IsZero tells if the key hasn't been set
+func (key PrivateKey) IsZero() bool {
+	return len(key) == 0
 }
 
 // IsZero tells if the key hasn't been set
-func (k BinaryKey) IsZero() bool {
-	return len(k) == 0
+func (pub PublicKey) IsZero() bool {
+	return len(pub) == 0
+}
+
+// Equal checks if two private keys are identical
+func (key PrivateKey) Equal(alter PrivateKey) bool {
+	return bytes.Equal(key, alter)
+}
+
+// Equal checks if two public keys are identical
+func (pub PublicKey) Equal(alter PublicKey) bool {
+	return bytes.Equal(pub, alter)
+}
+
+// PrivateKeyFromBase64 decodes a base64-based string into
+// a [PrivateKey]
+func PrivateKeyFromBase64(data string) (PrivateKey, error) {
+	b, err := decodeKey(data, PrivateKeySize)
+	return b, err
+}
+
+// PublicKeyFromBase64 decodes a base64-based string into
+// a [PublicKey]
+func PublicKeyFromBase64(data string) (PublicKey, error) {
+	b, err := decodeKey(data, PublicKeySize)
+	return b, err
 }
 
-// Equal checks if two keys are identical
-func (k BinaryKey) Equal(alter BinaryKey) bool {
-	return bytes.Equal(k, alter)
+func encodeKey(b []byte) string {
+	switch {
+	case len(b) == 0:
+		return ""
+	default:
+		return base64.StdEncoding.EncodeToString(b)
+	}
 }
 
-// BinaryKeyFromBase64 decodes a base64-based string into
-// a [BinaryKey]
-func BinaryKeyFromBase64(data string) (BinaryKey, error) {
+func decodeKey(data string, size int) ([]byte, error) {
 	b, err := base64.StdEncoding.DecodeString(data)
-	return BinaryKey(b), err
+	switch {
+	case err != nil:
+		return []byte{}, err
+	case len(b) != size:
+		err = ErrInvalidKeySize
+		return []byte{}, err
+	default:
+		return b, nil
+	}
 }
 
 // KeyPair holds a Key pair
 type KeyPair struct {
-	PrivateKey BinaryKey
-	PublicKey  BinaryKey
+	PrivateKey PrivateKey
+	PublicKey  PublicKey
 }