Into the symmetry

tl;dr if you are using go-jose , node-jose , jose2go , Nimbus JOSE+JWT or jose4j with ECDH-ES please update to the latest version. RFC 7516 aka JSON Web Encryption (JWE) hence many software libraries implementing this specification used to suffer from a classic Invalid Curve Attack . This would allow an attacker to completely recover the secret key of a party using JWE with Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) , where the sender could extract receiver’s private key. Premise In this blog post I assume you are already knowledgeable about elliptic curves and their use in cryptography. If not Nick Sullivan 's A (Relatively Easy To Understand) Primer on Elliptic Curve Cryptography or Andrea Corbellini's series Elliptic Curve Cryptography: finite fields and discrete logarithms are great starting points. Then if you further want to climb the elliptic learning curve including the related attacks you might also want to visit https://s...

tl;dr   I was able to hijack the OAuth tokens of EVERY Paypal OAuth application with a really simple trick. Introduction If you have been following this blog you might have got tired of how many times  I have stressed out the importance of the redirect_uri parameter in the OAuth flow. This simple parameter might be source of many headaches for any maintainer of OAuth installations being it a client or a server. Accepting the risk of repeating myself here is two simple suggestions that may help you stay away from troubles (you can always skip this part and going directly to the Paypal Vulnerability section): If you are building an OAuth client,   Thou shall register a redirect_uri as much as specific as you can i.e. if your OAuth client callback is https://yourouauthclient.com/oauth/oauthprovider/callback then DO register https://yourouauthclient.com/oauth/oauthprovider/callback   NOT JUST h ttps://yourouauthclient.com/ or https://yourouau...

Back in January I posed a question "to the Internet": What the heck is RFC 5114? It looks like a lot happened since then around it. I would like to use this post to recollect some of the stuff around RFC5114 . Chapter 0: October 2007 RFC5114 draft was submitted to the IETF . Chapter I: January 2016 In short RFC5114 is an IETF Informational RTC that " describes eight Diffie-Hellman groups that can be used in conjunction with IETF protocols to provide security for Internet communications. " . One of the thing about this RTC that attracted the attention of many (and also mine) is that violates the Nothing up my sleeve principle. The other peculiar thing about this RTC (that caught my attention) was that the P s specified for groups 22/23/24 were not safe primes but were indeed DSA primes adapted to Diffie Hellman. So far so good. Except that all the p-1 specified for those groups factored in a really nice way! So I decided to intensify a bit my r...

By Justin Richer and Antonio Sanso  This article was excerpted from the book OAuth 2 in Action . The OAuth core specification specifies four different grant types: Authorization Code , Implicit , Resource Owner Password Credentials and Client Credentials . Each grant type is designed with different security and deployment aspects in mind and should be used accordingly.  For example, the Implicit grant flow is to be used by OAuth clients where the client code executes within the user agent environment. Such clients are generally JavaScript-only applications, which have, of course, limited capability of hiding the client_secret in client-side code running in the browser. At the other side of the spectrum there are classic server-side applications that can use the authorization code grant type and can safely store the client_secret somewhere in the server. What about native applications then?  Native applications are those that run directly on the end user’s...

If you bought the book I have been writing with Justin Richer namely OAuth 2 in Action you might have noticed that we will never got tired to stress out how much important the redirect_uri is in the OAuth 2 universe. Failing to understand this (rather simple) concept might  lead to disasters. The redirect_uri is really central in the two most common OAuth flows ( authorization code and implicit grant ). I have blogged about redirect_uri related vulnerability several times and both in OAuth client and OAuth server context.  Developing an OAuth client is notoriously easier to develop compare to the server counter part. Said that the OAuth client implementer should still take care and master some concepts.  If I would be limited to give a single warning for OAuth client implementer this would be  If you are building an OAuth client,   Thou shall register a redirect_uri as much as specific as you can or simply less formally " The registe...

Last Google Chrome release for Chrome 50.0.2661.75 contains the fix for a security low bug I found (CVE-2016-1658). When first I found this bug I was under the impression it could be an UXSS. Quickly after I reported I started to realize that this wasn't as exploitable though. The issue per se was extremely easy to reproduce: Create an HTML file that looks like and save it (e.g. chrome.html) <h1>Hi</h1>  <script> alert(document.domain)</script> Now supposing the file is saved under (in MacOS) /Users/xxx/Downloads/chrome.html open the file from hard disk in this way:   file://mail.google.com/Users/xxx/Downloads/chrome.html   Note: mail.google.com is arbitrary . This can be any domain (hence is universal)  Observe the document.domain alerted is mail.google.com!  Observe the cookies transported are the one associated with *.google.com domain : Now this looked really weird to me and I reported as an...

Usual Mandatory Disclaimer: IANAC (I am not a cryptographer) so I might likely end up writing a bunch of mistakes in this blog post... tl;dr The OpenSSL 1.0.2 releases suffer from a Key Recovery Attack on DH small subgroups . This issue got assigned CVE-2016-0701 with a severity of High and OpenSSL 1.0.2 users should upgrade to 1.0.2f. If an application is using DH configured with parameters based on primes that are not "safe" or not Lim-Lee (as the one in RFC 5114 ) and either Static DH ciphersuites are used or DHE ciphersuites with the default OpenSSL configuration (in particular SSL_OP_SINGLE_DH_USE is not set) then is vulnerable to this attack.  It is believed that many popular applications (e.g. Apache mod_ssl) do set the  SSL_OP_SINGLE_DH_USE option and would therefore not be at risk (for DHE ciphersuites), they still might be for Static DH ciphersuites. Introduction So if you are still here it means you wanna know more. And here is the thing. In my last bl...