Re: WebCrypto with ECMAScript 5.1?

I am not sure that I parsed your question or motivation correctly; will try
to answer it two different ways:

(a) If your environment doesn't have Promises, then necessarily your
environment does not provide a native implementation of Web Crypto either
(certainly not the version in the latest draft).

In that case you would need to provide Web Crypto as a polyfill too, and so
the question really is:
"are there security risks to using Web Crypto polyfill XXX rather than
built in platform support?"

Yes -- It depends on your polyfill, but assuming a Javascript-side
implementation you should consider:

  * Implementation quality of the polyfill (is it a mature library that
properly implements cryptographic primitives)
  * Does your security model require unextractable keys (a Javascript
polyfill almost surely cannot provide this; there are also subtle
challenges like not revealing keying material due to non-constant timing of
operations, for which all bets are off in a JS runtime environment).

(b) If on the other hand your question is specifically about whether
ECMAScript 6 provides important security features needed for Web Crypto,
then the answer is No. The use of Promises for instance does not provide
any security benefits. In fact earlier versions of the spec did not use
Promises.

On Tue, Aug 2, 2016 at 6:50 PM, Waitzman, David (Contractor) <
David_Waitzman@comcast.com> wrote:

> I want to use WebCrypto, Encrypted Media Extensions, and Media Source
> Extensions in a context where only ECMAScript 5.1 is required.  So I need
> to at least use a polyfill for Promise, as it is an ECMAScript 6 feature.
> Any other polyfills that I would need?  Would any of those polyfill(s)
> somehow introduce a security risk that would not be present if ECMAScript 6
> was instead used?
>
> Thanks,
> --
> David Waitzman
> Envieta Systems LLC
>
>