Re: [jose] #4: Remove wrapped keys from integrity check (allow separation of keys from data)

"jose issue tracker" <trac+jose@trac.tools.ietf.org> Wed, 03 April 2013 19:52 UTC

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Subject: Re: [jose] #4: Remove wrapped keys from integrity check (allow separation of keys from data)
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#4: Remove wrapped keys from integrity check (allow separation of keys from
data)


Comment (by michael.jones@microsoft.com):

 This write-up is missing the fact that even if the wrapped keys were
 removed from the integrity calculation, there's still per-recipient
 content in the headers, such as information about the key used for that
 recipient.  So I believe what you're really asking for, Richard, is to
 remove both the wrapped key and the header from the integrity calculation,
 so there is no per-recipient information protected.  (Please correct me if
 I'm wrong.)

 For starters, not protecting the headers could open us up to algorithm
 substitution attacks, because the "alg" and/or "enc" values could be
 modified by the attacker.

 Furthermore, protecting the headers cryptographically binds the
 information in them to the Ciphertext, which is a very good thing.
 Especially given that we've now allowed additional information to be
 passed in the headers (by saying that header parameter values that are not
 understood must be ignored), I fully expect that some of that information
 will only be of any value when cryptographically bound to the Ciphertext,
 so attackers cannot modify it.

 Protecting the headers values is a "secure by default" architecture.  It
 removes the need to ask questions about what attacks are enabled if header
 parameter A or header parameter B can be modified by the attacker, because
 we've taken that possibility away from the attacker.  Especially given
 that we know that we don't know what all the header parameters will be,
 from a security viewpoint, continuing to protect them seems like the only
 sensible choice.

-- 
-------------------------+-------------------------------------------------
 Reporter:               |       Owner:  draft-ietf-jose-json-web-
  rbarnes@bbn.com        |  encryption@tools.ietf.org
     Type:  defect       |      Status:  new
 Priority:  major        |   Milestone:
Component:  json-web-    |     Version:
  encryption             |  Resolution:
 Severity:  Active WG    |
  Document               |
 Keywords:               |
-------------------------+-------------------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/jose/trac/ticket/4#comment:3>
jose <http://tools.ietf.org/jose/>