From: Chris Duncan <chris@zoso.dev>
Date: Tue, 29 Jul 2025 09:34:04 +0000 (-0700)
Subject: Refactor BIP-39 mnemonic generation from strings to bitwise operations.
X-Git-Tag: v0.10.5~48^2~10
X-Git-Url: https://git.codecow.com/?a=commitdiff_plain;h=23caf4905453a7e83b3bb433a267504df8aaaed5;p=libnemo.git

Refactor BIP-39 mnemonic generation from strings to bitwise operations.
---

diff --git a/src/lib/bip39-mnemonic.ts b/src/lib/bip39-mnemonic.ts
index 46a36d1..785f743 100644
--- a/src/lib/bip39-mnemonic.ts
+++ b/src/lib/bip39-mnemonic.ts
@@ -3,7 +3,7 @@
 
 import { Bip39Words } from './bip39-wordlist'
 import { BIP39_ITERATIONS } from './constants'
-import { bin, bytes, dec, utf8 } from './convert'
+import { bin, bytes, dec, hex, utf8 } from './convert'
 import { Entropy } from './entropy'
 import { Key } from '#types'
 
@@ -54,16 +54,26 @@ export class Bip39Mnemonic {
 	* @param {string} entropy - Hexadecimal string
 	* @returns {string} Mnemonic phrase created using the BIP-39 wordlist
 	*/
-	static async fromEntropy (entropy: string): Promise<Bip39Mnemonic> {
-		const e = await Entropy.import(entropy)
-		const checksum = await this.checksum(e)
-		let concatenation = `${e.bits}${checksum}`
+	static async fromEntropy (entropy: Key): Promise<Bip39Mnemonic> {
+		if (typeof entropy === 'string') entropy = hex.toBytes(entropy)
+		if (![16, 20, 24, 28, 32].includes(entropy.byteLength)) {
+			throw new RangeError('Invalid entropy byte length for BIP-39')
+		}
+		const phraseLength = 0.75 * entropy.byteLength
+		const checksum = await this.checksum(entropy)
+
+		let e = 0n
+		for (let i = 0; i < entropy.byteLength; i++) {
+			e = e << 8n | BigInt(entropy[i])
+		}
+
+		let concatenation = (e << BigInt(entropy.byteLength) / 4n) | checksum
 		const words: string[] = []
-		while (concatenation.length > 0) {
-			const wordBits = concatenation.substring(0, 11)
-			const wordIndex = parseInt(wordBits, 2)
-			words.push(Bip39Words[wordIndex])
-			concatenation = concatenation.substring(11)
+		for (let i = 0; i < phraseLength; i++) {
+			const wordBits = concatenation & 2047n
+			const wordIndex = Number(wordBits)
+			words.unshift(Bip39Words[wordIndex])
+			concatenation >>= 11n
 		}
 		const sentence = words.join(' ')
 		return this.fromPhrase(sentence)
@@ -76,12 +86,10 @@ export class Bip39Mnemonic {
 	 * @param {Entropy} entropy - Cryptographically strong pseudorandom data of length N bits
 	 * @returns {Promise<string>} First N/32 bits of the hash as a hexadecimal string
 	 */
-	static async checksum (entropy: Entropy): Promise<string> {
-		const hashBuffer = await globalThis.crypto.subtle.digest('SHA-256', entropy.bytes)
-		const hashBytes = new Uint8Array(hashBuffer)
-		const hashBits = bytes.toBin(hashBytes)
-		const checksumLength = entropy.bits.length / 32
-		const checksum = hashBits.substring(0, checksumLength)
+	static async checksum (entropy: Uint8Array<ArrayBuffer>): Promise<bigint> {
+		const sha256sum = new Uint8Array(await crypto.subtle.digest('SHA-256', entropy))[0]
+		const checksumBitLength = BigInt(entropy.byteLength) / 4n
+		const checksum = BigInt(sha256sum) >> (8n - checksumBitLength)
 		return checksum
 	}
 
@@ -131,9 +139,9 @@ export class Bip39Mnemonic {
 		}
 
 		const entropy = await Entropy.import(bin.toBytes(entropyBits))
-		const expectedChecksum = await this.checksum(entropy)
+		const expectedChecksum = await this.checksum(entropy.bytes)
 
-		if (expectedChecksum !== checksumBits) {
+		if (Number(expectedChecksum) !== parseInt(checksumBits, 2)) {
 			return false
 		}