RE: Implementing RSACryptoServiceProvider *and* JavaScript

From: Glenn (Glenn_at_discussions.microsoft.com)
Date: 11/26/04 

Date: Thu, 25 Nov 2004 21:31:02 -0800

One of the things I discovered is the 'standard' RSA algorithms, as
implemented in http://www.leemon.com/crypto/bigInt.html for example, WILL
NOT DECRYPT using the .net RSACryptoServiceProvider. I've been working on
the idea that .NET encrypts using OAEP or PKCS, but still need to research
this.

The bottom line is if you use the .NET-generated public keys in the leemon
example to encrypt a known string (e.g. "hello") and then compare this with
the output from .NET. THEY'RE DIFFERENT.

I've more-or-less come to the conclusion that the RSACryptoServiceProvider
is more trouble than it's worth, so I'm going to use the bigint.cs code
from the http://www.codeproject.com/csharp/TotalSecurity.asp article as I
need to guarentee the client and server code to be compatible, and it's
risky relying on Microsoft to not change the algorithm when they feel like it
(that's assuming I'll ever get the damn thing working in the first place).

Regards,
Glenn

"Patricio Jutard" wrote:

> Glenn, this is a good idea to overcome the problem of having to pay the SSL
> Certificate, here in Argentina, costs are a big issue that usualy stops
> clients from buying our software. Your solution of trying to simulate a SSL
> style mechanism is great and I would like to help you in order to make this
> work.
> Could you please tell me what JavaScript RSA implementations you found and
> point me to them so I can start helping?
>
> Thanks,
>
> Patricio Jutard
>
> "Glenn" wrote:
>
> > I'm currently trying to strengthen up the security on a large ASP.NET
> > application (a web content management system). The primary objective is to
> > prevent people from evesdropping for passwords and other sensitive
> > information, with a secondary objective of preventing Harry the Hacker from
> > having his (her) evil way.
> >
> > Logging on is secured by never storing the passwords in plain text and using
> > a combination of MD5 hashes for the user/password, and a single-use token to
> > 'salt' the resultant hash. This is secure as the password (or its hash) are
> > completely obscured by the salt.
> >
> > The next step -- and I'm *really* surprised that *everyone* doesn't do this
> > -- is to prevent 'Evil Eve' from listening in to the network when the
> > passwords and other sensitive information is passed from the client back to
> > the server. At this point I should point out that SSL isn't an option
> > because of its cost. The application is aimed at small businesses who baulk
> > at the thought of paying $400/year for a certificate (it's hard enough
> > getting $500 out of them for the website!). Also it is often not possible to
> > implement SSL on public shared web servers.
> >
> > The way I propose this to work is as follows:
> >
> > 1) The server creates a RSACryptoServiceProvider object and keeps this as an
> > application variable. When the object is created, it creates the public and
> > private keys.
> >
> > 2) When the user requests the form to change a password, the form is
> > rendered with a JavaScript RSA implementation and with the *public* keys
> > embedded in the form (probably in the onSubmit event). Note that Java or
> > ActiveX is absolutely out of the question, therefore I can only implement
> > RSA on the client in JavaScript.
> >
> > 3) On the client, the user fills in the form and the onSubmit event takes
> > the variables and encrypts them using the JavaScript RSA implementation using
> > the supplied public keys. The existing form fields are cleared (don't want
> > the plain text information being passed over!). The RSA encrypted field is
> > sent back to the server.
> >
> > 4) On the server the RSACryptoServiceProvider object is called to decrypt
> > the data sent from the client using the *private* keys.
> >
> > 5) Voila!
> >
> > The strength of this is based on RSA and the fact that you can't break 1024
> > bit encryption (without an enormous effort). Although it will take a couple
> > of seconds to encrypt the data on the client, this doesn't matter.
> >
> > Having hunted around the internet, I keep drawing a blank here. There are
> > several implementations of RSA on JavaScript, but none of them are compatible
> > with the RSACryptoServiceProvider object. The bottom line is there's some
> > enormous numbers involved here (1024 bits worth!), so there's a shed load of
> > scary maths involved.
> >
> > I would *really* appreciate it if someone could point me in the direction of
> > a JavaScript RSA implementation that works with the RSACryptoServiceProvider.
> >
> > Oh, as a footnote, I'm really surprised that this isn't a common
> > requirement. It seems so obvious and so cheap; well it would be if I could
> > get the damn thing working!
> >
> >
> > TIA,
> > Glenn
> >

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