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diff --git a/pipermail/pycrypto/2012q3/000621.html b/pipermail/pycrypto/2012q3/000621.html new file mode 100644 index 0000000..f0c239e --- /dev/null +++ b/pipermail/pycrypto/2012q3/000621.html @@ -0,0 +1,117 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<HTML> + <HEAD> + <TITLE> [pycrypto] PyCrypto ElGamal code questions/comments + </TITLE> + <LINK REL="Index" HREF="index.html" > + <LINK REL="made" HREF="mailto:pycrypto%40lists.dlitz.net?Subject=Re%3A%20%5Bpycrypto%5D%20PyCrypto%20ElGamal%20code%20questions/comments&In-Reply-To=%3CCAGfyce3E8CeMkYVmJeigFu5fig%2B6ZnidMFM3aD4SQ%3DyYW6836w%40mail.gmail.com%3E"> + <META NAME="robots" CONTENT="index,nofollow"> + <style type="text/css"> + pre { + white-space: pre-wrap; /* css-2.1, curent FF, Opera, Safari */ + } + </style> + <META http-equiv="Content-Type" content="text/html; charset=us-ascii"> + <LINK REL="Previous" HREF="000615.html"> + <LINK REL="Next" HREF="000616.html"> + </HEAD> + <BODY BGCOLOR="#ffffff"> + <H1>[pycrypto] PyCrypto ElGamal code questions/comments</H1> + <B>Legrandin</B> + <A HREF="mailto:pycrypto%40lists.dlitz.net?Subject=Re%3A%20%5Bpycrypto%5D%20PyCrypto%20ElGamal%20code%20questions/comments&In-Reply-To=%3CCAGfyce3E8CeMkYVmJeigFu5fig%2B6ZnidMFM3aD4SQ%3DyYW6836w%40mail.gmail.com%3E" + TITLE="[pycrypto] PyCrypto ElGamal code questions/comments">gooksankoo at hoiptorrow.mailexpire.com + </A><BR> + <I>Sun Aug 5 09:55:25 EDT 2012</I> + <P><UL> + <LI>Previous message: <A HREF="000615.html">[pycrypto] PyCrypto ElGamal code questions/comments +</A></li> + <LI>Next message: <A HREF="000616.html">[pycrypto] problems with testing PyCrypto Module +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#621">[ date ]</a> + <a href="thread.html#621">[ thread ]</a> + <a href="subject.html#621">[ subject ]</a> + <a href="author.html#621">[ author ]</a> + </LI> + </UL> + <HR> +<!--beginarticle--> +<PRE>Hi Yaron, + +Some comments inline: + + +><i> * The documentation of "generate" says that randfunc returns X random +</I>><i> bytes. I think this should be bits. +</I>><i> +</I> +I am not 100% sure, but a common idiom in pycrypto is: + +" +if randfunc is None: + randfunc = Random.new().read +" + +so randfunc(N) returns N bytes of full entropy. + + * The "generate" function is way too conservative. We construct p as +><i> 2*q+1, where both p and q are prime. This makes p a classic "safe +</I>><i> prime". It also makes two of the checks redundant: g cannot divide +</I>><i> p-1, because only 2 and q divide it. g cannot be 2, and most likely +</I>><i> will not be q during the lifetime of the universe. I believe that +</I>><i> similarly, g**-1 cannot divide p-1, but my algebra skills are too +</I>><i> rusty to prove it. +</I>><i> +</I> +I contributed to that part with a patch. My intention was actually to list +in the loop +as many criteria as possible that a generator safe for both Elgamal +encryption and Elgamal signatures (because .generate() does not know how +the key will be used) must fulfill. + +It's true they are redundant in practice, but I think it's good to leave a +track behind with the general conditions that one must check, regardless of +how the domain parameters are computed. + + * For the same reasons, there is no need for the loop when +><i> constructing K (the secret parameter), e.g. on line #342. You just +</I>><i> need to ensure that it is an odd number, otherwise its GCD with p-1 +</I>><i> would be 2. So choose a random t, 2 < t < q-1, and let K=2*t+1. No +</I>><i> need for a loop or for the GCD calculation. +</I>><i> +</I> +In the _sign() method I see only a loop to ensure that residues remains in +the range 0..p-1. The loop does not contribute to GDC computation. + + +><i> * An important check is missing: the message M needs to be less than +</I>><i> p, both when signing and certainly when encrypting it. +</I>><i> +</I> +True. Note that M must not the message when signing with PyCrypto's +Elgamal. It must be really be the cryptographic hash of the message. +-------------- next part -------------- +An HTML attachment was scrubbed... +URL: <<A HREF="http://lists.dlitz.net/pipermail/pycrypto/attachments/20120805/4792d29c/attachment.html">http://lists.dlitz.net/pipermail/pycrypto/attachments/20120805/4792d29c/attachment.html</A>> +</PRE> + +<!--endarticle--> + <HR> + <P><UL> + <!--threads--> + <LI>Previous message: <A HREF="000615.html">[pycrypto] PyCrypto ElGamal code questions/comments +</A></li> + <LI>Next message: <A HREF="000616.html">[pycrypto] problems with testing PyCrypto Module +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#621">[ date ]</a> + <a href="thread.html#621">[ thread ]</a> + <a href="subject.html#621">[ subject ]</a> + <a href="author.html#621">[ 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> |