Check out the new USENIX Web site. The Eternal Resource Locator
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It would be clumsy to insist on the signature of whole web pages, so instead we propose to use HTML elements [HTML] to define the borders of the hashed section of the document as well as other features of the hashing mechanism:

 

  figure33


Figure 1: Publishing medical information. The publisher issues a catalogue every few months which lists all titles published, together with their hash values. The hash of the catalogue has to be distributed a trusted way, by being published in a paper journal, and signed using a long-term key.

Simplified, the way to protect part of the web page will look like:

<HTML>
...
<HASHBODY>
...
The examination results for the second MB
degree examination are as follows:
...
...
<HASH
URL="http://www.med.abc.ac.uk/examresults"
METHOD="SHA-1"
PARENT="http://www.cert.bma.org.uk">
<HASH
URL="http://www.med.abc.ac.uk/examresults"
METHOD="TIGER"
PARENT="http://www.cert.med.ac.uk">

</HASHBODY>

<HASH METHOD="SHA-1" VALUE="12345678..."
PARENT="http://www.cert.bma.org.uk">
<HASH METHOD="TIGER" VALUE="987654321..."
PARENT="http://www.cert.med.ac.uk">
...
</HTML>

One of the URLs that refer to this page might look something like:

...see <A
HREF="http://www.med.abc.ac.uk/examresults"
HASHMETHOD="TIGER" HASHVALUE="987654321..."
HASHPARENT="http://www.cert.med.ac.uk">here </A>for the list of candidates who have
satisfied the requirements for the degrees
of MB and BS.

Checking a hash involves computing the hash value on all the bytes of an HTML document between the hash-input border tags and comparing the HTML document's URL against the value specified within the hash-input. This value is then verified against the value held in the reference in the parent document.

We call this URL-with-hash combination an ERL or `eternal resource locator' as it makes static objects unique for ever. Dynamic objects are slightly more complex.



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Fabien A.P. Petitcolas, Computer Laboratory, University of Cambridge