Nathaniel S. H. Brown wrote:
On Thu, Sep 29, 2005 at 10:02:00PM -0700, Nathaniel S. H. Brown wrote:
I have created a very unique, yet simple method of a form
encryption
that provides the same mechanism that the public/private
key entails.
Check out my just published release at
http://www.nshb.net/secure-form-post-with-javascript-without-ssl
erm... this sounds like a plain old challenge-response
mechanism. Or maybe I don't understand what you mean with
"private key" and "public key" in your description.
Surprise, surprise. I had no idea about this RFC. The principles of RFC 2195
are exactly along the same lines as what I had implemented with the web
post. However, it seems as though the downside is that the secret with my
1.0 as well as the RFC 2195 has to be available in plain text at both ends
exclusively.
Within the news post referenced above, I made alluded to the next iteration,
which involves a more complex and secure authentication mechanism which does
not require the password to be stored as plain text within the database, but
will still be used on the client side as they need to manually acknowledge
they know what it is to properly authenticate. Only on the client computer
which creates the hash that is transmitted has access to the clear text
password.
To adjust the system would be quite simple. Based on a fixed username, when
a user creates or changes their password, the password field associated to
that user record would store a md5(username+password) in the database. Now,
on the client side, it uses a precomputed hash as the password which
combines the clear text password with the username combined to form the
hash. So on the form, the insertHash JavaScript function would md5(username
+ md5(username + password) + timestamp + publicKey), and on the reverse, the
server side script would compare against md5(post.username +
database.password + post.timestamp + post.publickey).
This would result in the password being stored in an encrypted, MD5 format
within the database, and still transmit the private key (password) through
the same fashion as CRAM-MD5 in a double layer MD5 hash ensuring its
security.
- Nathan
The core problem with any security mechanism that is implemented using
"stuff" (Javascript, Java applet, etc) that is downloaded from the
server that you are visiting is that any man in the middle attack can
simply remove that mechanism, and substitute it with their own.
e.g. My bank logon script performs an MD5 hash of the username and
password before sending it to the bank. The MITM tricks me to visiting
their own site, and just "proxies" the comms to the real site. However,
they strip out the MD5 hashing script,and replace it with an "identity"
function (i.e. the output is the same as the input). When the MITM
receives the form submission, it is trivial for them to extract the
username and password from the form, replace it with the MD5 hash
expected, and pass it on to the real bank.
I had started implementing/experimenting with using Secure Remote
Password (http://srp.stanford.edu/) for authentication to a secure web
site, with the idea that the password is never transmitted in clear, or
in a recoverable form. However, this stumbling point convinced me that
I'd be wasting my time!
One reason that SSL client certs offer real protection is that they are
not controllable by page content, and do not rely on something that
comes down from the site you are visiting.
Regards,
Rogan
