From 37b79ccde1241d36662e0aff9c249bf55c8226cb Mon Sep 17 00:00:00 2001
From: Lee Miller <lee.miller@tutanota.com>
Date: Sun, 25 Dec 2022 00:20:37 +0200
Subject: [PATCH] Add additional functions:

encodePublic(publicKey), decodePublic(publicKey) used in
encrypt() and decrypt() respectively - to comply with the network.

Minor formatting change.
---
 index.js | 66 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 47 insertions(+), 19 deletions(-)

diff --git a/index.js b/index.js
index a63218b..6095df4 100644
--- a/index.js
+++ b/index.js
@@ -5,12 +5,15 @@
 
 "use strict";
 
-const EC_GROUP_ORDER = Buffer.from('fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141', 'hex');
+const EC_GROUP_ORDER = Buffer.from(
+  'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141', 'hex');
 const ZERO32 = Buffer.alloc(32, 0);
 
+const curve_secp256k1 = 714,
+      key_length = 32;
+
 var promise = typeof Promise === "undefined" ?
-              require("es6-promise").Promise :
-              Promise;
+    require("es6-promise").Promise : Promise;
 var crypto = require("crypto");
 // try to use secp256k1, fallback to browser implementation
 try {
@@ -25,7 +28,7 @@ try {
   }
 }
 
-function isScalar (x) {
+function isScalar(x) {
   return Buffer.isBuffer(x) && x.length === 32;
 }
 
@@ -117,6 +120,29 @@ var getPublic = exports.getPublic = function(privateKey) {
   return secp256k1.publicKeyConvert(compressed, false);
 };
 
+// to comply with the bitmessage network
+function encodePublic(publicKey) {
+  assert(publicKey.length === 65, "Bad public key");
+  var buf = Buffer.alloc(70);
+  buf.writeUInt16BE(curve_secp256k1, 0, true);
+  buf.writeUInt16BE(key_length, 2, true);
+  publicKey.copy(buf, 4, 1, 33);
+  buf.writeUInt16BE(key_length, 36, true);
+  publicKey.copy(buf, 38, 33, 65);
+  return buf;
+}
+
+function decodePublic(publicKey) {
+  assert(publicKey.readUInt16BE(0, true) === curve_secp256k1, "Wrong curve!");
+  assert(publicKey.readUInt16BE(2, true) === key_length, "Bad key length!");
+  assert(publicKey.readUInt16BE(36, true) === key_length, "Bad key length!");
+  var buf = Buffer.alloc(65);
+  buf[0] = 0x04;
+  publicKey.copy(buf, 1, 4, 36);
+  publicKey.copy(buf, 33, 38, 70);
+  return buf;
+}
+
 /**
  * Get compressed version of public key.
  */
@@ -213,7 +239,7 @@ exports.encrypt = function(publicKeyTo, msg, opts) {
     {
       ephemPrivateKey = opts.ephemPrivateKey || crypto.randomBytes(32);
     }
-    ephemPublicKey = getPublic(ephemPrivateKey);
+    ephemPublicKey = encodePublic(getPublic(ephemPrivateKey));
     resolve(derive(ephemPrivateKey, publicKeyTo));
   }).then(function(Px) {
     var hash = sha512(Px);
@@ -241,18 +267,20 @@ exports.encrypt = function(publicKeyTo, msg, opts) {
  * plaintext on successful decryption and rejects on failure.
  */
 exports.decrypt = function(privateKey, opts) {
-  return derive(privateKey, opts.ephemPublicKey).then(function(Px) {
-    assert(privateKey.length === 32, "Bad private key");
-    assert(isValidPrivateKey(privateKey), "Bad private key");
-    var hash = sha512(Px);
-    var encryptionKey = hash.slice(0, 32);
-    var macKey = hash.slice(32);
-    var dataToMac = Buffer.concat([
-      opts.iv,
-      opts.ephemPublicKey,
-      opts.ciphertext
-    ]);
-    var realMac = hmacSha256(macKey, dataToMac);
-    assert(equalConstTime(opts.mac, realMac), "Bad MAC"); return aes256CbcDecrypt(opts.iv, encryptionKey, opts.ciphertext);
-  });
+  return derive(
+    privateKey, decodePublic(opts.ephemPublicKey)).then(function(Px) {
+      assert(privateKey.length === 32, "Bad private key");
+      assert(isValidPrivateKey(privateKey), "Bad private key");
+      var hash = sha512(Px);
+      var encryptionKey = hash.slice(0, 32);
+      var macKey = hash.slice(32);
+      var dataToMac = Buffer.concat([
+	opts.iv,
+	opts.ephemPublicKey,
+	opts.ciphertext
+      ]);
+      var realMac = hmacSha256(macKey, dataToMac);
+      assert(equalConstTime(opts.mac, realMac), "Bad MAC");
+      return aes256CbcDecrypt(opts.iv, encryptionKey, opts.ciphertext);
+    });
 };