Add additional functions:

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

index.js

@@ -8,9 +8,13 @@
 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;
+    Promise;
+const struct = require("python-struct");
 var crypto = require("crypto");
 // try to use secp256k1, fallback to browser implementation
 try {
@@ -117,6 +121,33 @@ var getPublic = exports.getPublic = function(privateKey) {
   return secp256k1.publicKeyConvert(compressed, false);
 };
 
+// to comply with the bitmessage network
+function encodePublic(publicKey) {
+    return Buffer.concat([
+	struct.pack('!H', curve_secp256k1),
+	struct.pack('!H', key_length),
+	publicKey.slice(1, 33),
+	struct.pack('!H', key_length),
+	publicKey.slice(33),
+    ]);
+};
+
+function decodePublic(publicKey) {
+    var i = 0;
+    var curve = struct.unpack('!H', publicKey.slice(i, i + 2))[0];
+    assert(curve == curve_secp256k1, "Wrong curve!");
+    i += 2;
+    var tmplen = struct.unpack('!H', publicKey.slice(i, i + 2))[0];
+    assert(tmplen == key_length, "Bad key length!");
+    i += 2;
+    var publicKeyX = publicKey.slice(i, i + tmplen);
+    i += tmplen;
+    tmplen = struct.unpack('!H', publicKey.slice(i, i + 2))[0];
+    assert(tmplen == key_length, "Bad key length!");
+    var publicKeyY = publicKey.slice(i, i + tmplen);
+    return Buffer.concat([Buffer.from("04", "hex"), publicKeyX, publicKeyY]);
+};
+
 /**
  * Get compressed version of public key.
  */
@@ -213,7 +244,7 @@ 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);
@@ -241,7 +272,7 @@ 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) {
+    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);

package.json

@@ -50,10 +50,11 @@
     "mocha": "*"
   },
   "dependencies": {
-    "acorn": "7.1.1",
-    "elliptic": "6.5.4",
-    "es6-promise": "4.2.8",
-    "nan": "2.14.0"
+      "acorn": "7.1.1",
+      "elliptic": "6.5.4",
+      "es6-promise": "4.2.8",
+      "nan": "2.14.0",
+      "python-struct": "1.1.3"
   },
   "optionalDependencies": {
     "secp256k1": "3.7.1"