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Re: New attachments issues

From: <noah_mendelsohn@us.ibm.com>
Date: Thu, 12 Jun 2003 11:27:25 -0400
To: Rich Salz <rsalz@datapower.com>
Cc: "xml-dist-app@w3.org" <xml-dist-app@w3.org>
Message-ID: <OFFEFBAB50.0F207A53-ON85256D43.005167A3@lotus.com>

Rich Salz writes:

>> In another posting, Gudge asked by signing times. 
>> In most cases (i.e.,  assuming no tricky XSLT 
>> transforms involved), the cost of signing is 
>> ka+b, where a is the length of the data, and b 
>> is fixed based on the number of bits in the key.

Right.  And though not being a crypto expert, my impression is that 
constant b can in many cases be significant or dominate in lots of 
practical scenarios (though of course, there is always an a>b/k  for which 
the first term dominates.)  What I think is missing in Gudge's analysis i 
the potential conversion time to base 64, the associated lack of locality 
in memory access etc.  So, implemented in the naive way in which the 
entire "binary buffer" is first converted to characters, then signed, I 
would assume:

Let's assume the original binary buffer was of length lbin, then the 
performance of signing that without conversion would be:


applying Rich's formula.  The cost of converting and signing as chars 
would be:

        c*lbin+k*(lbin*1.3)+b = (c+1.3*k)lbin+b

where c is the conversion time for a byte of binary into 1.3 bytes of 
characters.  Depending on how it's actually done, the memory usage might 
go up from lbin to 2.3 lbin, possibly affecting locality, cache hit 
ratios, etc. for large buffers.  Of course, a careful implementation would 
pipeline the conversions and only have a modest number of bytes in 
character form at a time.

Do I have this right?

BTW (off topic):  Rich, I really liked your article at 
http://webservices.xml.com/pub/a/ws/2003/06/10/salz.html .

Noah Mendelsohn                              Voice: 1-617-693-4036
IBM Corporation                                Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Received on Thursday, 12 June 2003 11:28:47 UTC

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