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Re: hashing

• To: David Megginson <dmeggin@a...>
• Subject: Re: hashing
• From: Rich Salz <rsalz@d...>
• Date: Thu, 29 Apr 2004 22:34:20 -0400 (EDT)
• Cc: XML Developers List <xml-dev@l...>
• In-reply-to: <40916503.9080001@a...>

If you're concerned about byte-for-byte identical, hashing each file
is okay; if you're concerned about semantic identical (e.g., the order
of attributes doesn't matter) than use standard XML canonicalization
or something similar (but it won't be as good:)

Her's a portable python script that compares all files named on
the command-line:

; cat x.py
import sys,sha
from xml.dom.ext.reader import PyExpat
from xml.dom.ext.c14n import Canonicalize

hashes = {}
for f in sys.argv:
    o = sha.sha()
    if 1:
        # simple hash of contents
        o.update(open(f).read())
    else:
        # sha(c14n(doc))
        r = PyExpat.Reader()
        dom = r.fromStream(open(f))
        o.update(Canonicalize(dom))
    h = o.digest()
    other = hashes.get(h, None)
    if other:
        print 'duplicate', f, other
    else:
        hashes[h] = f
;

--
Rich Salz                  Chief Security Architect
DataPower Technology       http://www.datapower.com
XS40 XML Security Gateway  http://www.datapower.com/products/xs40.html
XML Security Overview      http://www.datapower.com/xmldev/xmlsecurity.html

• References:
  • Re: hashing
    • From: David Megginson <dmeggin@a...>

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