[tahoe-dev] [tahoe-lafs] #750: deterministic IV for writecaps for dir entries

[tahoe-lafs]

#750: deterministic IV for writecaps for dir entries
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     Reporter:  zooko          |       Owner:                 
         Type:  enhancement    |      Status:  closed         
     Priority:  major          |   Milestone:  1.5.0          
    Component:  code-dirnodes  |     Version:  1.4.1          
   Resolution:  fixed          |    Keywords:  confidentiality
Launchpad_bug:                 |  
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Comment(by warner):

 oh, I'm being stupid and the new code is bad. What we're doing is
 encrypting a list of child writecaps in such a way that the containing
 dirnode's writecap is required to retrieve them. Obviously each child
 writecap must be encrypted with a different key. It is reasonable to use
 the hash of the child writecap as a salt (since there's no requirement
 that the constant child writecap be encrypted differently each time), but
 it is not ok to use the hash of the parent dirnode writecap as a salt
 (because that's the same for all children).

 My suggested change is wrong too.

 The code needs to be more like:

 {{{
 salt = hashutil.mutable_rwcap_iv_hash(rwcap)
 key = hashutil.mutable_rwcap_key_hash(salt, self._node.get_writekey())
 crypto = AES(key)
 }}}

 I'll make this change soon.

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Ticket URL: <http://allmydata.org/trac/tahoe/ticket/750#comment:4>
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