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Subject: Re: [office] Re: encryption

The reason to allow more than one algorithm, aside from preferences 
(individual, corporate, national requirements etc.) is that an attack 
could be found against any one of these algorithms and you don't want to 
be in a situation where the only algorithms specified are weak or broken. 
The use of SHA1, in particular, does not seem to be a good algorithm 

Of course, this doesn't mean you need to leave it open ended.

It really boils down to three questions:

1) For each algorithm type (hash, encryption, etc.), what unique 
identifier to we associate with each algorithm?

2) For the sake of encouraging interoperability do we recommend or mandate 
that a subset of these algorithms be supported?

3) Do we allow implementation-defined algorithms beyond those which we 
have assigned identifiers to?

But remember, there is nothing in the standard that mandates the support 
of the document encryption feature at all, so #2 doesn't really help us 
much here, does it?


Bob Jolliffe <bobjolliffe@gmail.com>
Ming Fei Jia <jiamingf@cn.ibm.com>
09/01/2009 12:39 PM
Re: [office] Re: encryption

Thanks Ming Fei.  You summarized my concerns much better than I ..

What was the original intent in specifying SHA1 and Blowfish?  It seems to 
me, though I wasn't around at the time, that the idea was primarily to 
ensure interoperability, perhaps above other plausible goals.  The 
selection of a widely available public domain cipher seems to reinforce 
that interpretation.

The casualty of interoperability here was choice.  There was no choice.  
By allowing documented algorithms (as per xmlenc-core) we open the window 
of choice slightly whilst maintaining some hope of interoperability.  This 
seems like it might be a good thing.

By opening up the third option (implementation defined algorithms) we 
maximize the choice but, as Ming Fei says, we risk the standard having no 
meaning or relevance regarding encryption.  This might be reasonable 
tradeoff under some conditions.  In the case of hashed passwords there is 
use case of conversion of legacy documents (which I'm still not that 
comfiortable with).  In the case of encrypted XML streams I don't think 
the same argument applies.

Is this perhaps yet another case for discrimination on the grounds of 
conformance class, where the use of an implementation defined algorithm is 
not disbarred, but it is treated essentially as an extension conforming to 
a different, less strict, class of document?


2009/9/1 Ming Fei Jia <jiamingf@cn.ibm.com>
In the proposal:
The defined value for the "algorithm" attribute is 3 options:
? The Blowfish algorithm in CFB mode.
? An IRI defined in 5.2 or 5.3 of [xmlenc-core]: The algorithm specified 
in 5.2 or 5.3 of [xmlenc-core] for this IRI.
? An IRI specifying an implementation defined algorithm.
Actually I think the proposal means ODF has no restriction for encryption 
algorithm and ODF encryption algorithm could be anything. Then, does the 
standard have meaning here? Of course, that is OK if there is some 
exception that everyone believes:
(1)Encryption algorithm does not have any interoperability issue in 
(2)Encryption algorithm will have no interoperability issue in the future
(3)Implementation defined algorithm is not conforming to ODF
(4)Standard here can not solve problems at all even the issues are there.
or anything else?

We could have some trade-off for the real complexity, but I suggest to be 
careful to evaluate this extending. thanks a lot.
Best Regards,

Mingfei Jia(???)
IBM Lotus Symphony Development
IBM China Software Development LAB, Beijing
Tel: 86-10-82452493 Fax: 86-10-82452887
NOTES:Ming Fei Jia/China/IBM E-mail: jiamingf@cn.ibm.com
Address: No.28 Building, Zhong Guan Cun Software Park, No.8 Dong Bei Wang 
West Road, ShangDi, Haidian District, Beijing 100193, P.R.China 

Bob Jolliffe ---2009-08-31 22:46:31---In addition - I don't know the 
answer to this, but in the interest of uniformity, is there also an IRI 
which can used to indica


Bob Jolliffe <bobjolliffe@gmail.com>




2009-08-31 22:46


[office] Re: encryption

In addition - I don't know the answer to this, but in the interest of 
uniformity, is there also an IRI which can used to indicate blowfish?  
Then we are clear the value of the attribute is an IRI.

2009/8/31 Bob Jolliffe <bobjolliffe@gmail.com> 
what I was trying to say on the call is that we now have 3 options for 
each algorithm, including a catchall "implementation defined" IRI.  I 
would prefer to see this last option allowed but not recommended.


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