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Re: Idea for securityfix in HTML

From: Goetz Bock <bock@blacknet.de>
Date: Sun, 17 Nov 2002 02:43:27 +0100
To: www-forms@w3.org
Message-ID: <20021117024327.F1167@zealot.blacknet.de>



Dear Mr. Xatr0z,

please get a copy of "secrets and lies" and read it to figure out why
what you suggest is A REALY BAD IDEA.

On Sat, Nov 16 '02 at 12:28, Xatr0z wrote:
> [ ... ] If someone is "sniffing" and get's the HTTP request
> instead of the HTTP server, he or she doesn't get the password, but it's
> encrypted (or with MD5, that depends on the HTTP request). Ofcourse, it
> isn't secure, he or she could trie an dictionary or brute-force attack, but
> is is more secure, and I think that's a good thing.
I don't need to do and brute-force. I can just reuse the SAME md5
hash/checksum I just sniffed to reauthenticate as a valid user. As we
have discussed, an MD5 sum can not be "decrypted" into the real
password, it can only be compatred to a given MD5 sum in the database.

In Unix, there is a SALT used to make the md5 sum for a given password
different if used by user A and B. When you log in, the password you
typed is salted (one possible salt is added), md5ed and compared to the
stored value. If it matched, youre logged in, otehrwise a different slat
is tried. If all possible salts (usually just a char, e.g. 256 tries)
were tried, and none matched, youre not logged in.

This can not be done for HTML. There you can only store one value, and
than send THIS stored value. What you could do is to implment one of the
"no-secrets-told" authentication mechanisms, but than you'd better use
https. It's better understood and therefore more secure (it does not per
so add client authentication and is ususally open to man in the middle
attacs due to user errors ... oh well)

> What do you feel about the idea to create a attribute which allows the
> client to send an (MD5) checksum of the file, to determine if the transport
> went well?
This does not even add integrity checks for anything but transport
errors. This should be handled by the transport protocoll (TCP/IP in 
this case) but again read "secrets and lies".
-- 
Goetz Bock       (c) 2002 as     blacknet.de - Munich - Germany   /"\
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Received on Saturday, 16 November 2002 21:09:10 GMT

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