Add seed version prefix constant

src/index.js

@@ -1,5 +1,8 @@
+const crypto = require('crypto');
 const bip39 = require('bip39');
 
+const PREFIX = [0xC2, 0xFE, 0x58];
+
 const P2PKH = 0x00;
 const P2WPKHP2SH = 0x01;
 const P2WPKH = 0x02;
@@ -8,22 +11,23 @@ const bip39v = {
 	versions: {P2PKH, P2WPKHP2SH, P2WPKH}
 };
 
-const getEntropyBuffer = mnemonic => Buffer.from(
-	bip39.mnemonicToEntropy(mnemonic),
-	'hex'
-);
-
-bip39v.generateMnemonic = (length, versionByte = P2PKH) => {
-	const entropy = getEntropyBuffer(bip39.generateMnemonic(length));
-	entropy[0] = versionByte;
+bip39v.generateMnemonic = (length = 224, versionByte = P2PKH) => {
+	const buffer = Buffer.concat([
+		Buffer.from(PREFIX),
+		Buffer.from([versionByte]),
+		crypto.randomBytes(length / 8)
+	]);
 
-	return bip39.entropyToMnemonic(entropy);
+	return bip39.entropyToMnemonic(buffer);
 };
 
 bip39v.mnemonicToVersionByte = mnemonic => {
-	const entropy = getEntropyBuffer(mnemonic);
+	const buffer = Buffer.from(
+		bip39.mnemonicToEntropy(mnemonic),
+		'hex'
+	);
 
-	return entropy[0];
+	return buffer[PREFIX.length];
 };
 
 bip39v.mnemonicToVersion = mnemonic => {

test/unit.js

@@ -8,9 +8,9 @@ const fixtures = {
 		P2WPKH: 0x02
 	},
 	mnemonics: {
-		P2PKH: 'above rack wait angle thank ribbon strategy gallery silk leave brave swarm',
-		P2WPKHP2SH: 'abuse lottery polar torch prison option common common mix moon wonder length',
-		P2WPKH: 'across sword flip inspire allow joke skate drip icon lady emerge toss',
+		P2PKH: 'seed version abandon bus rebuild logic connect wise illegal traffic transfer olympic royal style equal',
+		P2WPKHP2SH: 'seed version about math twice crater force critic grace panic party label flag draft sketch',
+		P2WPKH: 'seed version absent reward pipe sketch clarify sight spread addict divorce idle burst alarm tide',
 		UNKNOWN: 'such galaxy much glimpse music turkey toward exhaust filter key pilot hello'
 	}
 };
@@ -19,16 +19,15 @@ test('bip39v is exported', t => {
 	t.not(bip39v, undefined);
 });
 
-test('bip39v.generateMnemonic() defaults to 12 words', t => {
-	t.is(bip39v.generateMnemonic().split(' ').length, 12);
+test('bip39v.generateMnemonic() defaults to 24 words', t => {
+	t.is(bip39v.generateMnemonic().split(' ').length, 24);
 });
 
 test('bip39v.generateMnemonic(length) generates different length mnemonics', t => {
-	t.is(bip39v.generateMnemonic(128).split(' ').length, 12);
-	t.is(bip39v.generateMnemonic(160).split(' ').length, 15);
-	t.is(bip39v.generateMnemonic(192).split(' ').length, 18);
-	t.is(bip39v.generateMnemonic(224).split(' ').length, 21);
-	t.is(bip39v.generateMnemonic(256).split(' ').length, 24);
+	t.is(bip39v.generateMnemonic(128).split(' ').length, 15);
+	t.is(bip39v.generateMnemonic(160).split(' ').length, 18);
+	t.is(bip39v.generateMnemonic(192).split(' ').length, 21);
+	t.is(bip39v.generateMnemonic(224).split(' ').length, 24);
 });
 
 test('bip39v.generateMnemonic() defaults to P2PKH version byte', t => {
@@ -52,7 +51,7 @@ test('bip39v.generateMnemonic(length, version) adds correct version', t => {
 test('bip39v.mnemonicToVersionByte(mnemonic) against fixture data', t => {
 	Object.entries(fixtures.mnemonics).forEach(([version, mnemonic]) => {
 		const versionByte = bip39v.mnemonicToVersionByte(mnemonic);
-		const expectedVersionByte = version === 'UNKNOWN' ? 0xD8 : fixtures.versionBytes[version];
+		const expectedVersionByte = version === 'UNKNOWN' ? 0x44 : fixtures.versionBytes[version];
 		t.is(versionByte, expectedVersionByte);
 	});
 });