window.crypto.getRandomValues doesn't seem to work in IE11 for me (although the function exists).
OpenPGP.js throws SCRIPT5022: No secure random number generator available.

But there is a ms object called window.msCrypto.getRandomValues(), which works with OpenPGP.js.
I tested both functions manually using "window.(ms)[C]rypto.getRandomValues(new Uint32Array(10))" with the same result, msCrypto works, crypto doesn't.