The addition of WebCrypto to the browser enables a number of interesting client server opportunities that did not exist prior. One of which I think is interesting is what I have been calling browser bound certificates.
Now neither of these scenarios necessarily prescribe the use of X.509 certificates but considering signed PDF’s are the defacto-standard for signed documents and S/MIME is supported by Android, IOS, Windows Phones and Outlook it seems its not totally silly to say this approach has at least some merit.
To implement both of these one needs to have support for X.509 and its concepts within the browser, this is where Browser Bound certificates and PKIjs comes in. Imagine a client authenticating a user and over that authenticated session the client submits a certificate request bound to that session that is passed to an API on the server side that issues the client a X.509 certificate.
With that the client now has all the material that is necessary to sign and/or encrypt messages on the client side using the formats already in use. The web can interoperate with the desktop.
In our theoretical application need to take all the traditional precautions for both web and crypto-aware applications some of which include:
- Not mixing content from other domains,
- Loading the site and all of its resources over SSL,
- Segmenting the signing and verification code with postMessage,
- Using crypto primitives in safe ways,
- Using non-exportable keys,
- Keeping the keys short-lived.
But we can with these Browser Bound certificates build modern PKI aware applications that have great user experience that can even work without the server being present once provisioned.