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diff --git a/pipermail/pycrypto/2009q1/000068.html b/pipermail/pycrypto/2009q1/000068.html new file mode 100644 index 0000000..2d98d3e --- /dev/null +++ b/pipermail/pycrypto/2009q1/000068.html @@ -0,0 +1,129 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML> + <HEAD> + <TITLE> [pycrypto] Quick and Easy Email Authentication + </TITLE> + <LINK REL="Index" HREF="index.html" > + <LINK REL="made" HREF="mailto:pycrypto%40lists.dlitz.net?Subject=%5Bpycrypto%5D%20Quick%20and%20Easy%20Email%20Authentication&In-Reply-To=5.2.1.1.0.20090201143122.03f7e130%40plus.pop.mail.yahoo.com"> + <META NAME="robots" CONTENT="index,nofollow"> + <META http-equiv="Content-Type" content="text/html; charset=us-ascii"> + <LINK REL="Previous" HREF="000060.html"> + <LINK REL="Next" HREF="000069.html"> + </HEAD> + <BODY BGCOLOR="#ffffff"> + <H1>[pycrypto] Quick and Easy Email Authentication</H1> + <B>David MacQuigg</B> + <A HREF="mailto:pycrypto%40lists.dlitz.net?Subject=%5Bpycrypto%5D%20Quick%20and%20Easy%20Email%20Authentication&In-Reply-To=5.2.1.1.0.20090201143122.03f7e130%40plus.pop.mail.yahoo.com" + TITLE="[pycrypto] Quick and Easy Email Authentication">macquigg at ece.arizona.edu + </A><BR> + <I>Wed Feb 11 09:41:54 CST 2009</I> + <P><UL> + <LI>Previous message: <A HREF="000060.html">[pycrypto] Quick and Easy Email Authentication +</A></li> + <LI>Next message: <A HREF="000069.html">[pycrypto] Quick and Easy Email Authentication +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#68">[ date ]</a> + <a href="thread.html#68">[ thread ]</a> + <a href="subject.html#68">[ subject ]</a> + <a href="author.html#68">[ author ]</a> + </LI> + </UL> + <HR> +<!--beginarticle--> +<PRE>I think there is a fundamental problem with what I am proposing below. +The cipher text (authcode) has to be much longer than the four bytes I've +shown in the example, or it will be trivial to break. Before giving up +on this approach, I thought I would check with the crypto experts on this +list. Am I missing something simple, maybe a different algorithm than +RSA, maybe some way to do this with hashcodes? If we can solve this +problem, it could lead to a robust, no-exceptions policy on +authentication of SMTP mail sessions. + +Let me try to state the problem in more fundamental terms. A stranger +says HELO this is f33faf76.mailout09.arizona.edu. The only other +information you have to verify that claim is a DNS text record at +mailout09.arizona.edu. That record can hold up to 480 bytes of text. + +The authcode can be a little longer than f33faf76, but the longer we make +it, the less likely senders will use it in their HELO commands. The +shorter we make it, the more likely forgers will be able to produce a +valid authcode by brute force methods. A lot depends on how long we +expect the authcode to remain valid. The scheme I suggested below +returned a timestamp valid for only a few seconds, making it impractical +to try 2**32 possible authcodes. Yes, I know it can be done with +massively parallel processors, but our requirement is only enough +security to quickly screen out 99% of the forged IDs presented by petty +criminals. More secure sites can add additional checks, including a +digital signature on the entire message. + +-- Dave +************************************************************ * +* David MacQuigg, PhD email: macquigg at ece.arizona.edu * * +* Research Associate phone: USA 520-721-4583 * * * +* ECE Department, University of Arizona * * * +* 9320 East Mikelyn Lane * * * +* <A HREF="http://purl.net/macquigg">http://purl.net/macquigg</A> Tucson, Arizona 85710 * +************************************************************ * + + +At 04:30 PM 2/1/2009 -0700, David MacQuigg wrote: + +><i>I'm working on an email authentication system that needs a little more +</I>><i>security. The idea is that a sender will include an authentication code +</I>><i>in the very first command to request an email session. For example, +</I>><i>arizona.edu might include the code 'f33faf76' as in: +</I>><i>. +</I>><i>. HELO IDf33faf76.mailout09.arizona.edu +</I>><i>. +</I>><i>The receiver can then verify that this is not a forgery by getting a DNS +</I>><i>record from mailout09.arizona.edu. The simplest way to do this is for +</I>><i>arizona.edu to publish that code verbatim, and change it frequently. It +</I>><i>won't take long, however, for the crooks to modify their zombies to query +</I>><i>the DNS records at the victim domain, and use the same code in their +</I>><i>forged HELO commands. +</I>><i> +</I>><i>So what we really need in the sender's DNS record is not the actual code, +</I>><i>but a public key that can be used to decrypt the code and prove not only +</I>><i>that it was generated by the alleged sender, but it was generated +</I>><i>recently, like within a few seconds of when the HELO command was sent. +</I>><i> +</I>><i>I'm trying to figure out how to do this with PyCrypto, but the API +</I>><i>documentation is not much help. It would be nice to have an example +</I>><i>showing encryption and decryption using RSA. +</I>><i> +</I>><i>Here are the stub functions I'm using: +</I>><i>. +</I>><i>. def encrypt(plaintext, privkey): +</I>><i>. return 'f33faf76' +</I>><i>. +</I>><i>. def decrypt(authcode, pubkey): +</I>><i>. return '315:14:45:03' # day:hour:minute:second +</I>><i>. +</I>><i>Help will be greatly appreciated. I'll be glad to help with +</I>><i>documentation, once I understand how this package is used. +</I> + +</PRE> + + +<!--endarticle--> + <HR> + <P><UL> + <!--threads--> + <LI>Previous message: <A HREF="000060.html">[pycrypto] Quick and Easy Email Authentication +</A></li> + <LI>Next message: <A HREF="000069.html">[pycrypto] Quick and Easy Email Authentication +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#68">[ date ]</a> + <a href="thread.html#68">[ thread ]</a> + <a href="subject.html#68">[ subject ]</a> + <a href="author.html#68">[ author ]</a> + </LI> + </UL> + +<hr> +<a href="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">More information about the pycrypto +mailing list</a><br> +</body></html> |