OAuth “dance” - server side flow

Getting some inspiration from this dialog about OAuth 1.0 I thought it would be nice to have something similar for OAuth 2.0

The Actors

The R.O. shows intent

Alice (R.O.): hey, Bob , I would like you to be able to access the profile pictures from my Facebook account so you can print for me a nice photo album.
Bob (client): no problem, I know how we can do it. All I need is you getting me an Authorization Code from Facebook.

The R.O. obtain an authorization code

Alice (R.O.): hey Mark, www.printondemand.biz wants an Authorization Code
Mark (server): are you sure you want to give this code to www.printondemand.biz?
this will allow it to get all profile pictures from your profile.
Alice (R.O.): yes it is ok.
Mark (server): ok I am sending you over to www.printondemand.biz

The R.O. is redirected to the client

Alice (R.O.): hey Bob here we go, this is the Authorization Code
Bob (client): thanks

The client exchange the Authorization Code for an
Access Token

Bob (client): hey Mark, I would like to trade my Authorization Code for an Access Token
Mark (server): hey Bob here we go

The client access the protected resource

Bob (client): hey Mark, give me the profile pictures, here is the
Access Token
Mark (server): here you are

Comments

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tl;dr Mozilla Firefox prior to version 72 suffers from Small Subgroups Key Recovery Attack on DH in the WebCrypto 's API. The Firefox's team fixed the issue r emoving completely support for DH over finite fields (that is not in the WebCrypto standard). If you find this interesting read further below. Premise In this blog post I assume you are already knowledgeable about Diffie-Hellman over finite fields and related attacks. If not I recommend to read any cryptography book that covers public key cryptography. Here is a really cool simple explanation by David Wong : I found a cooler way to explain Diffie-Hellman :D pic.twitter.com/DlPvGwZbto — David Wong (@cryptodavidw) January 4, 2020 If you want more details about Small Subgroups Key Recovery Attack on DH I covered some background in one of my previous post ( OpenSSL Key Recovery Attack on DH small subgroups (CVE-2016-0701) ). There is also an academic pape r where we examine the issue with some more rigors.

Into the symmetry

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