ethers.js/src.ts/wallet/mnemonic.ts

import { pbkdf2, sha256 } from "../crypto/index.js";
import {
    defineProperties, getBytes, hexlify, assertNormalize, assertPrivate, assertArgument, toUtf8Bytes
} from "../utils/index.js";
import { LangEn } from "../wordlists/lang-en.js";

import type { BytesLike } from "../utils/index.js";
import type { Wordlist } from "../wordlists/index.js";


// Returns a byte with the MSB bits set
function getUpperMask(bits: number): number {
   return ((1 << bits) - 1) << (8 - bits) & 0xff;
}

// Returns a byte with the LSB bits set
function getLowerMask(bits: number): number {
   return ((1 << bits) - 1) & 0xff;
}


function mnemonicToEntropy(mnemonic: string, wordlist?: null | Wordlist): string {
    assertNormalize("NFKD");

    if (wordlist == null) { wordlist = LangEn.wordlist(); }

    const words = wordlist.split(mnemonic);
    assertArgument((words.length % 3) === 0 && words.length >= 12 && words.length <= 24,
        "invalid mnemonic length", "mnemonic", "[ REDACTED ]");

    const entropy = new Uint8Array(Math.ceil(11 * words.length / 8));

    let offset = 0;
    for (let i = 0; i < words.length; i++) {
        let index = wordlist.getWordIndex(words[i].normalize("NFKD"));
        assertArgument(index >= 0, `invalid mnemonic word at index ${ i }`, "mnemonic", "[ REDACTED ]");

        for (let bit = 0; bit < 11; bit++) {
            if (index & (1 << (10 - bit))) {
                entropy[offset >> 3] |= (1 << (7 - (offset % 8)));
            }
            offset++;
        }
    }

    const entropyBits = 32 * words.length / 3;


    const checksumBits = words.length / 3;
    const checksumMask = getUpperMask(checksumBits);

    const checksum = getBytes(sha256(entropy.slice(0, entropyBits / 8)))[0] & checksumMask;

    assertArgument(checksum === (entropy[entropy.length - 1] & checksumMask),
        "invalid mnemonic checksum", "mnemonic", "[ REDACTED ]");

    return hexlify(entropy.slice(0, entropyBits / 8));
}

function entropyToMnemonic(entropy: Uint8Array, wordlist?: null | Wordlist): string {

    assertArgument((entropy.length % 4) === 0 && entropy.length >= 16 && entropy.length <= 32,
        "invalid entropy size", "entropy", "[ REDACTED ]");

    if (wordlist == null) { wordlist = LangEn.wordlist(); }

    const indices: Array<number> = [ 0 ];

    let remainingBits = 11;
    for (let i = 0; i < entropy.length; i++) {

        // Consume the whole byte (with still more to go)
        if (remainingBits > 8) {
            indices[indices.length - 1] <<= 8;
            indices[indices.length - 1] |= entropy[i];

            remainingBits -= 8;

        // This byte will complete an 11-bit index
        } else {
            indices[indices.length - 1] <<= remainingBits;
            indices[indices.length - 1] |= entropy[i] >> (8 - remainingBits);

            // Start the next word
            indices.push(entropy[i] & getLowerMask(8 - remainingBits));

            remainingBits += 3;
        }
    }

    // Compute the checksum bits
    const checksumBits = entropy.length / 4;
    const checksum = parseInt(sha256(entropy).substring(2, 4), 16) & getUpperMask(checksumBits);

    // Shift the checksum into the word indices
    indices[indices.length - 1] <<= checksumBits;
    indices[indices.length - 1] |= (checksum >> (8 - checksumBits));

    return wordlist.join(indices.map((index) => (<Wordlist>wordlist).getWord(index)));
}

const _guard = { };

/**
 *  A **Mnemonic** wraps all properties required to compute [[link-bip39]]
 *  seeds and convert between phrases and entropy.
 */
export class Mnemonic {
    /**
     *  The mnemonic phrase of 12, 15, 18, 21 or 24 words.
     *
     *  Use the [[wordlist]] ``split`` method to get the individual words.
     */
    readonly phrase!: string;

    /**
     *  The password used for this mnemonic. If no password is used this
     *  is the empty string (i.e. ``""``) as per the specification.
     */
    readonly password!: string;

    /**
     *  The wordlist for this mnemonic.
     */
    readonly wordlist!: Wordlist;

    /**
     *  The underlying entropy which the mnemonic encodes.
     */
    readonly entropy!: string;

    /**
     *  @private
     */
    constructor(guard: any, entropy: string, phrase: string, password?: null | string, wordlist?: null | Wordlist) {
        if (password == null) { password = ""; }
        if (wordlist == null) { wordlist = LangEn.wordlist(); }
        assertPrivate(guard, _guard, "Mnemonic");
        defineProperties<Mnemonic>(this, { phrase, password, wordlist, entropy });
    }

    /**
     *  Returns the seed for the mnemonic.
     */
    computeSeed(): string {
        const salt = toUtf8Bytes("mnemonic" + this.password, "NFKD");
        return pbkdf2(toUtf8Bytes(this.phrase, "NFKD"), salt, 2048, 64, "sha512");
    }

    /**
     *  Creates a new Mnemonic for the %%phrase%%.
     *
     *  The default %%password%% is the empty string and the default
     *  wordlist is the [English wordlists](LangEn).
     */
    static fromPhrase(phrase: string, password?: null | string, wordlist?: null | Wordlist): Mnemonic {
        // Normalize the case and space; throws if invalid
        const entropy = mnemonicToEntropy(phrase, wordlist);
        phrase = entropyToMnemonic(getBytes(entropy), wordlist);
        return new Mnemonic(_guard, entropy, phrase, password, wordlist);
    }

    /**
     *  Create a new **Mnemonic** from the %%entropy%%.
     *
     *  The default %%password%% is the empty string and the default
     *  wordlist is the [English wordlists](LangEn).
     */
    static fromEntropy(_entropy: BytesLike, password?: null | string, wordlist?: null | Wordlist): Mnemonic {
        const entropy = getBytes(_entropy, "entropy");
        const phrase = entropyToMnemonic(entropy, wordlist);
        return new Mnemonic(_guard, hexlify(entropy), phrase, password, wordlist);
    }

    /**
     *  Returns the phrase for %%mnemonic%%.
     */
    static entropyToPhrase(_entropy: BytesLike, wordlist?: null | Wordlist): string {
        const entropy = getBytes(_entropy, "entropy");
        return entropyToMnemonic(entropy, wordlist);
    }

    /**
     *  Returns the entropy for %%phrase%%.
     */
    static phraseToEntropy(phrase: string, wordlist?: null | Wordlist): string {
        return mnemonicToEntropy(phrase, wordlist);
    }

    /**
     *  Returns true if %%phrase%% is a valid [[link-bip39]] phrase.
     *
     *  This checks all the provided words belong to the %%wordlist%%,
     *  that the length is valid and the checksum is correct.
     */
    static isValidMnemonic(phrase: string, wordlist?: null | Wordlist): boolean {
        try {
            mnemonicToEntropy(phrase, wordlist);
            return true;
        } catch (error) { }
        return false;
    }
}