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diff --git a/pipermail/pycrypto/2012q4/000636.html b/pipermail/pycrypto/2012q4/000636.html new file mode 100644 index 0000000..3cc4bdf --- /dev/null +++ b/pipermail/pycrypto/2012q4/000636.html @@ -0,0 +1,174 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<HTML> + <HEAD> + <TITLE> [pycrypto] Confused about some code in PubKey/RSA/_slowmath.py + </TITLE> + <LINK REL="Index" HREF="index.html" > + <LINK REL="made" HREF="mailto:pycrypto%40lists.dlitz.net?Subject=Re%3A%20%5Bpycrypto%5D%20Confused%20about%20some%20code%20in%20PubKey/RSA/_slowmath.py&In-Reply-To=%3C014FF57C-5925-48A9-A611-23CDB11AD4AC%40gmail.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="000635.html"> + <LINK REL="Next" HREF="000648.html"> + </HEAD> + <BODY BGCOLOR="#ffffff"> + <H1>[pycrypto] Confused about some code in PubKey/RSA/_slowmath.py</H1> + <B>Shoufu Luo</B> + <A HREF="mailto:pycrypto%40lists.dlitz.net?Subject=Re%3A%20%5Bpycrypto%5D%20Confused%20about%20some%20code%20in%20PubKey/RSA/_slowmath.py&In-Reply-To=%3C014FF57C-5925-48A9-A611-23CDB11AD4AC%40gmail.com%3E" + TITLE="[pycrypto] Confused about some code in PubKey/RSA/_slowmath.py">luoshoufu at gmail.com + </A><BR> + <I>Tue Nov 6 17:24:42 PST 2012</I> + <P><UL> + <LI>Previous message: <A HREF="000635.html">[pycrypto] Confused about some code in PubKey/RSA/_slowmath.py +</A></li> + <LI>Next message: <A HREF="000648.html">[pycrypto] jython and pycrpto installation on windows +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#636">[ date ]</a> + <a href="thread.html#636">[ thread ]</a> + <a href="subject.html#636">[ subject ]</a> + <a href="author.html#636">[ author ]</a> + </LI> + </UL> + <HR> +<!--beginarticle--> +<PRE>Hi Lorenz, + +Thank you so much for explanation. Now, I think I understand the code. + +The private key is only for decryption and sign, and public key is for encryption and verify. The _sign procedure calls the decryption (which I though should be encryption function), because decrypt and encrypt are the same operation from mathematical standpoint. Yes, that is the confusing part, but diligent! Now, I'm clear.Thank you! + +And thank you for advice, I use private key for signature in the standard way not for encryption. My problem was solved. Thanks again. + + +Yours sincerely, +Shoufu + +On Nov 6, 2012, at 2:59 PM, Lorenz Quack wrote: + +Hi Shoufu, + +first things first: +A) Cryptography is *very* hard to get right even if use a crypto library. So if +you ask these questions out of curiosity or educational purposes that is fine but +please don't use your own crypto in production code where you really need security! + +B) I'm myself not a cryptography expert so take my answers with a grain of salt. + +First some general explanations that might be helpful. +For answers to your actual questions scroll down to the "---" mark. + +From a mathematical standpoint encryption and decryption are the same operation. +Namely raise a number (this is either your plain text "m" or your cipher text "c") +to an exponent modulo a large number (usually called "n"). The only difference is +what you take as the exponent. So in RSA you have two different exponents a private +one (let us call it "d") and a public one (let us call it "e"). combined with "n" +these are in essence your private and public key. So now we have one mathematical +operation but four variables ("m", "c", "d", and "e") giving you these combinations: + +1) m**e mod n --> encryption +2) m**d mod n --> sign +3) c**e mod n --> verify +4) c**d mod n --> decryption + +--- + +so to answer your first question: +"encrypting" using your private key is called signing. Think of it this way. if you +"encrypt" with your private key everybody would be able to decrypt it because what +could be done with your public key which is ... well *public* + +as for the second question: +this question seems to stem from the same misconception as the first one. +encryption happens with the *public* key and decryption with the *private* key. +Everybody (i.e. the public) is allowed to send you encrypted messages but only you +should be able to decrypt them in private! + +I hope that answers your questions. + +Sincerely yours, +Lorenz + + + +On 11/05/2012 06:26 AM, Shoufu Luo wrote: +><i> Hi all, +</I>><i> +</I>><i> I'm trying to encrypt a message with my private key and release the encrypted to +</I>><i> others who will use my public key to decrypt. But, I failed. +</I>><i> +</I>><i> I was confused by the follwing code from PubKey/RSA/_slowmath.py of pyCrypto-2.6. +</I>><i> If anyone can give any clues to answer the following questions, I will appreciate. +</I>><i> +</I>><i> 1. Theoretically, if I encrypt date using private key, I can decrypt the encrypted +</I>><i> data using public key, and vice versa. Why the key must be a private key in +</I>><i> decryption function, line 51-52? Can't I use private key to decrypt? +</I>><i> +</I>><i> 2. _sign() should be the signature process using private key to encrypt a piece of +</I>><i> data, why it is trying to decrypt at line 70, and it should be decryption in +</I>><i> '_verify', but why it is _encrypt()? +</I>><i> +</I>><i> 49 def _decrypt(self, c): +</I>><i> 50 # compute c**d (mod n) +</I>><i> 51 if not self.has_private(): +</I>><i> 52 raise TypeError("No private key") +</I>><i> 53 if (hasattr(self,'p') and hasattr(self,'q') and hasattr(self,'u')): +</I>><i> 54 m1 = pow(c, self.d % (self.p-1), self.p) +</I>><i> 55 m2 = pow(c, self.d % (self.q-1), self.q) +</I>><i> 56 h = m2 - m1 +</I>><i> 57 if (h<0): +</I>><i> 58 h = h + self.q +</I>><i> 59 h = h*self.u % self.q +</I>><i> 60 return h*self.p+m1 +</I>><i> 61 return pow(c, self.d, self.n) +</I>><i> 62 +</I>><i> 63 def _encrypt(self, m): +</I>><i> 64 # compute m**d (mod n) +</I>><i> 65 return pow(m, self.e, self.n) +</I>><i> 66 +</I>><i> 67 def _sign(self, m): # alias for _decrypt +</I>><i> 68 if not self.has_private(): +</I>><i> 69 raise TypeError("No private key") +</I>><i> 70 return self._decrypt(m) +</I>><i> 71 +</I>><i> 72 def _verify(self, m, sig): +</I>><i> 73 return self._encrypt(sig) == m +</I>><i> +</I>><i> +</I>><i> Thanks, +</I>><i> Shoufu +</I>><i> +</I> +_______________________________________________ +pycrypto mailing list +<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A> +<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A> + +</PRE> + + + +<!--endarticle--> + <HR> + <P><UL> + <!--threads--> + <LI>Previous message: <A HREF="000635.html">[pycrypto] Confused about some code in PubKey/RSA/_slowmath.py +</A></li> + <LI>Next message: <A HREF="000648.html">[pycrypto] jython and pycrpto installation on windows +</A></li> + <LI> <B>Messages sorted by:</B> + <a href="date.html#636">[ date ]</a> + <a href="thread.html#636">[ thread ]</a> + <a href="subject.html#636">[ subject ]</a> + <a href="author.html#636">[ 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> |