[Openid-specs-ab] Encryption

Nat Sakimura sakimura at gmail.com
Sat Oct 29 20:10:41 UTC 2011


HMACing with CEK and have that in JWE spec as REQUIRED in case of CBC would
be really nice.

Maybe I should post it in Jose list or bring it up in Taipei.

=nat via iPhone

On 2011/10/30, at 3:54, John Bradley <ve7jtb at ve7jtb.com> wrote:


On 2011-10-29, at 3:42 PM, Nat Sakimura wrote:



=nat via iPhone

On 2011/10/30, at 2:52, John Bradley <ve7jtb at ve7jtb.com> wrote:


The reality is that we are not going to be able to REQUIRE AES-GWC any time
soon.


+1 though keep pressuring the implementations to support GCM etc. should
continue.


I think that libraries not providing padding oracles and other side channels
is important to be clear about.

AES-CBC is still something important to support.

One possible combination is using zip


gzip I guess.


JWE refers to it as zip, but it is deflate in a gzip container (not zlib).
 I am looking for some better wording for the JWE spec.


with AES-CBC and not differentiating between padding and inflate errors.
 The CRC32 integrity check over the uncompressed source would foil the
oracle attack.


That should make it significantly harder though it may not be impossible.


There are a bunch of implementation details around error reporting that
would determine that.  one would be how you report invalid content type if
someone removed the zip flag from the envelope.

So perfect is hard,  however we do have other tools like reporting signing
and encrypting errors as a composite value where we encrypt a signed object.

GWC also has some issues with long cypher texts so is not pure magic on it's
own.

John B.



John B.
On 2011-10-29, at 7:17 AM, Rob Richards wrote:

Mike,

Do you have a patch for the support already? As long as there's no BC issues
I might be able to get it into the 5.4 candidate before it's released. I had
just started looking at adding support due to the xml enc issue but would be
extremely helpful if you already had a patch. Also if you happen to know
which openssl versions the patch works with as it appears there are a number
of ways to use GCM depending upon the version.

Rob

On 10/28/11 12:18 PM, Mike Jones wrote:

We pretty much reached the same conclusion during the encryption working
group session at IIW.  The only problem, as Nat pointed out, is that PHP
libraries, as currently distributed, do not support GCM (although the
underlying OpenSSL libraries that PHP uses do).  Of course, maybe we can use
this as a forcing function to get PHP to support GCM by default (without
requiring recompilation, which is possible now).


  -- Mike


-----Original Message-----

From: openid-specs-ab-bounces at lists.openid.net [mailto:
openid-specs-ab-bounces at lists.openid.net] On Behalf Of Anthony Nadalin

Sent: Friday, October 28, 2011 9:13 AM

To: Axel.Nennker at telekom.de; jbradley at mac.com

Cc: openid-specs-ab at lists.openid.net

Subject: Re: [Openid-specs-ab] Encryption


As I see it we need to require the GCM mode of operation (an authenticated
encryption mode) for AES (moving AES-GCM from option to mandatory).


-----Original Message-----

From: openid-specs-ab-bounces at lists.openid.net [mailto:
openid-specs-ab-bounces at lists.openid.net] On Behalf Of
Axel.Nennker at telekom.de

Sent: Friday, October 28, 2011 8:55 AM

To: jbradley at mac.com

Cc: openid-specs-ab at lists.openid.net

Subject: Re: [Openid-specs-ab] Encryption


Here is the link to the paper:

http://www.nds.rub.de/media/nds/veroeffentlichungen/2011/10/22/HowToBreakXMLenc.pdf


The authors recommend "One possibility to avoid our attack is to use a
symmetric cryptographic primitive that does not only provide
confidentiality, but also integrity. This can for instance be achieved by
replacing the CBC mode of operation with a mode that provides message
integrity. Adequate choices have for instance been standardized in ISO/IEC
19772:2009. We consider this solution as very recommendable for future
versions of the XML Encryption standard. Unfortunately, this may bring
deployment and backwards compatibility issues."


http://www.iso.org/iso/catalogue_detail?csnumber=46345


-Axel


-----Original Message-----

From: John Bradley [mailto:jbradley at mac.com]

Sent: Freitag, 28. Oktober 2011 16:22

To: Nennker, Axel

Cc: Nat Sakimura; Michael Jones; openid-specs-ab at lists.openid.net

Subject: Re: [Openid-specs-ab] Encryption


We don't encryption it, but we do support it.


I haven't seen the original paper only analysis of it.


Mike should be able to get it.


I don't think we should panic.   I have known about this for a week or so.


While the problem involves CBC it is not necessarily a CBC algorithm
vulnerability in itself.


The problem is likely the xmlenc API error messages and having them reported
back over SOAP.


As long as we are careful about not communicating too much in the error
message and implementers protect against side channel timing attacks, JWE
probably is OK as is with appropriate security considerations.


I would be surprised if the attack works agains AES-CBC + RSA.


It also probably is ineffective agains AES-CBC+keywrap.


Yes GWC is better that is why it was created.


We need the paper before trying to fix things that may not need fixing.


John B.





On 2011-10-28, at 10:13 AM, Axel.Nennker at telekom.de wrote:


Do we actually require encryption in the openid connect standards? I thought
we refer to JWS and JWS and that's it?

Axel





-----Original Message-----

From: openid-specs-ab-bounces at lists.openid.net

[mailto:openid-specs-ab-bounces at lists.openid.net] On Behalf Of

sakimura

Sent: Freitag, 28. Oktober 2011 13:36

To: Mike Jones; John Bradley; Anthony Nadalin; Openid specs ab

Subject: [Openid-specs-ab] Encryption


So I was going over the recent XML Encryption vulnerability.

http://www.informationweek.com/news/security/vulnerabilities/231901532


The flaw is that of CBC mode of operation combined with

unauthenticated encryption.

It is a kind of padding oracle attack.


We have two choices here:


1) Require authenticated encryption mode such as GCM

2) Require message authentication to be applied to the cipher text.


Ideally 1) should be taken as operational efficiency is much greater

than 2), but in reality we do not have support for GCM in many

languages.


Thus, while RECOMMENDing 1), we should REQUIRE HMAC to be applied on

the encrypted text (cipher text) in CBC mode.


Thus, we should make it REQUIRED to sig+enc+mac, instead of sig+enc,

and REQUIRE the verifier to first verify the mac and if the mac is not

correct the process should abend returning mac error.


Also, although same public-private keypair can be used for encryption

and signature in case of RSA, we should probably use two separate

keypair. That is safer.

Perhaps we would not REQUIRE it, but we should RECOMMEND it.


=nat


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