OASIS Open Document Format for Office Applications (OpenDocument) TC

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  • 1.  Re: [office] Proper identifier for Excel-style digest algorithm

    Posted 07-08-2008 07:04
    Hi,
    
    robert_weir@us.ibm.com wrote:
    > 
    > How does OOXML, in their revised text, refer to the legacy algorithm?  I 
    > thought they also supported modern algorithms now like SHA256.  So they 
    > must have some way of indicating or referring to the legacy algorithm. 
    >  It might not be a URI, but they must describe it somehow, right?  If 
    > all else fails, call it something like "ISO/IEC 29500 Legacy Hash".
    
    What we need is an URI, but we can define our own URI here if there is 
    none existing to identify this algorithm.
    
    > 
    > Ideally we would refer to either ISO/IEC 29500, section 3.3.1.81 or 
    >  Ecma-376 (second edition) whenever either one of those documents 
    > appears in a publicly viewable form.  I don't think we want to duplicate 
    > their algorithm definition if we can avoid doing so.  Better to 
    > reference what they already have, when it is corrected.
    
    I agree to this.
    > 
    > -Rob
    
    Michael
    -- 
    Michael Brauer, Technical Architect Software Engineering
    StarOffice/OpenOffice.org
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  • 2.  Re: [office] Proper identifier for Excel-style digest algorithm

    Posted 07-08-2008 08:32
    I agree.  What we would need is a URI.  But it would be better, if we do need to define a URI, that we do so in conjunction with ECMA ie. that they would then at some point use the same URI that we define.
    
    Though given my earlier post and the input from Doug, it does seems that this will be more of an application issue than an ODF issue.  If the intention is NOT to write out those legacy hashed passwords in an ODF document, then having a URI to refer to the algorithm is surely not such a major concern for ODF.
    
    Regards
    Bob
    
    ----- "Michael Brauer - Sun Germany - ham02 - Hamburg" 


  • 3.  Re: [office] Proper identifier for Excel-style digest algorithm

    Posted 07-08-2008 13:30


    Bob Jolliffe <bobj@dst.gov.za> wrote on 07/08/2008 04:13:16 AM:

    > I agree.  What we would need is a URI.  But it would be better, if
    > we do need to define a URI, that we do so in conjunction with ECMA
    > ie. that they would then at some point use the same URI that we define.
    >
    > Though given my earlier post and the input from Doug, it does seems
    > that this will be more of an application issue than an ODF issue.  
    > If the intention is NOT to write out those legacy hashed passwords
    > in an ODF document, then having a URI to refer to the algorithm is
    > surely not such a major concern for ODF.
    >

    If I recall, at the BRM they were trying to make the distinctions between translating a legacy document into OOXML (where the legacy hash may be written out in the OOXML document) versus creating a new OOXML document from scratch (where the legacy hash should not be used because it it known to be weak).  There was not time at the BRM to hash out (forgive the pun) the right language for this.

    I think we have a similar thing here.  When converting a legacy MS Office document to ODF, if the legacy document has protected sections, you don't have many good choices:

    1) Either Remove the protection (changes the functionality of the document)
    2) Or, set a new dummy password like "password" using a strong hash like SHA256 (pointless)
    3) Or, preserve the existing legacy hash value (but this hash is weak)

    No document encryption is involved.  This is simply a password hash.

    It seems that 3) is the least bad of these options.  

    We could add language to the standard that makes it clear that this algorithm is deprecated.

    -Rob  


  • 4.  Re: [office] Proper identifier for Excel-style digest algorithm

    Posted 07-09-2008 09:13
    As you say there are no good options here.  The paradigm of protecting sections with passwords in this way is broken.

    But there is a fourth option you can add.  The user interface, in this case through OpenOffice, alerts the user that the document contains a weakly hashed password and requests that a new one is entered upon saving.

    There would still be a difficulty with batch and automatic conversion - such as the many headless openoffice solutions.

    Your option 2 is not as pointless as you say.  Bear in mind that the hash is not protecting the document in any way.  Users might believe it is protecting the document but this a falsehood.  All it is protecting is the password.  We need to have a password in order to preserve the functionality of the document as you point out.  It is far better to have a pointless password than to perpetuate weak protection of a potentially valuable password.

    The better solution would be to sign the protected section.  You can then lock it in some way (using a silly password if you like).  The standard already makes this possible but signing sections is not implemented in any applications that I am aware of.

    Regards
    Bob