abi•14mo ago

Abusing prototype CryptoKey in `node:crypto`

Is there any way that I can set the prototype of an object to specifically CryptoKey as defined by node:crypto? I am trying to get around some nasty instanceof check in a third-party library which is getting in the way.

import * as krypto from "node:crypto";
Object.setPrototypeOf(foo, krypto.webcrypto.CryptoKey.prototype);

import * as krypto from "node:crypto";
Object.setPrototypeOf(foo, krypto.webcrypto.CryptoKey.prototype);

The above gives me this error:

error: Uncaught TypeError: Cannot read properties of undefined (reading 'prototype')

error: Uncaught TypeError: Cannot read properties of undefined (reading 'prototype')

3 Replies

abi•14mo ago

I also tried just ..., krypto.webcrypto.CryptoKey) but it's still undefined obviously and i'm not quite sure why I'm basically trying to get the type as found in [npm]/@types/node/18.11.18/crypto.d.ts:

interface Crypto {
    // ...
    CryptoKey: CryptoKeyConstructor;
}

// This constructor throws ILLEGAL_CONSTRUCTOR so it should not be newable.
interface CryptoKeyConstructor {
    /** Illegal constructor */
    (_: { readonly _: unique symbol }): never; // Allows instanceof to work but not be callable by the user.
    readonly length: 0;
    readonly name: 'CryptoKey';
    readonly prototype: CryptoKey;
}
/**
 * @since v15.0.0
 */
interface CryptoKey {

interface Crypto {
    // ...
    CryptoKey: CryptoKeyConstructor;
}

// This constructor throws ILLEGAL_CONSTRUCTOR so it should not be newable.
interface CryptoKeyConstructor {
    /** Illegal constructor */
    (_: { readonly _: unique symbol }): never; // Allows instanceof to work but not be callable by the user.
    readonly length: 0;
    readonly name: 'CryptoKey';
    readonly prototype: CryptoKey;
}
/**
 * @since v15.0.0
 */
interface CryptoKey {

Actually, looking back at how I even got here makes me question why I'm even doing it, because I'm calling krypto.webcrypto.subtle.importKey and then the return value of that should already be krypto.webcrypto.CryptoKey but this third-party library code does instanceof CryptoKey and says it's "a different" CryptoKey And so does krypto.KeyObject.from:

error: Uncaught TypeError: The "key" argument must be an instance of CryptoKey. Received an instance of CryptoKey
const keyObject = krypto.KeyObject.from(privateCryptoKey);

error: Uncaught TypeError: The "key" argument must be an instance of CryptoKey. Received an instance of CryptoKey
const keyObject = krypto.KeyObject.from(privateCryptoKey);

mmastrac•14mo ago

In this case, I suspect we're not actually exporting the CryptoKey prototype from the node:crypto polyfill which is probably a bug. We do export CryptoKey in the global namespace -- does this work?

Object.setPrototypeOf(foo, CryptoKey.prototype);

Object.setPrototypeOf(foo, CryptoKey.prototype);

abi•14mo ago

oof, sorry, didn't see your message until now! the whole problem is no more tbh, not exactly sure why, but if it pops back up, i will make sure to give that a try. (but i'm like 90% sure i tried it before and it failed!)