Comments for Alice and Bob in Cryptoland http://alicebob.cryptoland.net Fri, 06 Jan 2012 10:22:56 +0000 hourly 1 http://wordpress.org/?v=3.3.1 Comment on Understanding the Montgomery reduction algorithm by Conrado http://alicebob.cryptoland.net/understanding-the-montgomery-reduction-algorithm/#comment-320 Conrado Fri, 06 Jan 2012 10:22:56 +0000 http://alicebob.cryptoland.net/?p=220#comment-320 Oops. Thanks! Oops. Thanks!

]]> Comment on Understanding the Montgomery reduction algorithm by Martin http://alicebob.cryptoland.net/understanding-the-montgomery-reduction-algorithm/#comment-319 Martin Fri, 06 Jan 2012 08:48:47 +0000 http://alicebob.cryptoland.net/?p=220#comment-319 x * p[0] mod B = 1 not x * p[0] mod B = 0. x * p[0] mod B = 1
not x * p[0] mod B = 0.

]]> Comment on Understanding the Montgomery reduction algorithm by Conrado http://alicebob.cryptoland.net/understanding-the-montgomery-reduction-algorithm/#comment-318 Conrado Tue, 03 Jan 2012 01:19:10 +0000 http://alicebob.cryptoland.net/?p=220#comment-318 Sure! I am assuming that you are storing your numbers in byte vectors, therefore p[0] is the lower byte of the prime modulus. Then, 1/p[0] mod B is the inverse, modulo B, of p[0]; i.e. the number x such that x * p[0] mod B = 1. In order to compute it, you can use the <a href="http://alicebob.cryptoland.net/understanding-the-extended-euclidian-algorithm/" rel="nofollow">extended Euclidean algorithm</a>; but in your case you can simply compute x * p[0] mod B for all bytes x until the result is one. Sure! I am assuming that you are storing your numbers in byte vectors, therefore p[0] is the lower byte of the prime modulus. Then, 1/p[0] mod B is the inverse, modulo B, of p[0]; i.e. the number x such that x * p[0] mod B = 1. In order to compute it, you can use the extended Euclidean algorithm; but in your case you can simply compute x * p[0] mod B for all bytes x until the result is one.

]]> Comment on Understanding the Montgomery reduction algorithm by Daniel http://alicebob.cryptoland.net/understanding-the-montgomery-reduction-algorithm/#comment-317 Daniel Mon, 02 Jan 2012 23:48:18 +0000 http://alicebob.cryptoland.net/?p=220#comment-317 Can you go more in depth on "the magic number" section? I'm a little confused on how to calculate -(1/p[0]) mod B. I've got a little toy implementation that uses B=256. Can you go more in depth on “the magic number” section? I’m a little confused on how to calculate -(1/p[0]) mod B. I’ve got a little toy implementation that uses B=256.

]]> Comment on Understanding the extended Euclidean algorithm by Žilvinas http://alicebob.cryptoland.net/understanding-the-extended-euclidian-algorithm/#comment-315 Žilvinas Sat, 12 Nov 2011 19:31:08 +0000 http://alicebob.cryptoland.net/?p=213#comment-315 Thanks, helped a lot! Thanks, helped a lot!

]]> Comment on Closure gotcha (with Python) by O.C. http://alicebob.cryptoland.net/closure-gotcha-with-python/#comment-312 O.C. Sat, 23 Jul 2011 12:32:58 +0000 http://alicebob.cryptoland.net/?p=15#comment-312 Hi, thanks for this good explanation. I spent a few hours trying to find my bug and I finally used a debugger... then it was easy to see that the value was not the expected one. I wish I had used the debugger earlier! Hi,

thanks for this good explanation. I spent a few hours trying to find my bug and I finally used a debugger… then it was easy to see that the value was not the expected one. I wish I had used the debugger earlier!

]]> Comment on Closure gotcha (with Python) by Alex Marandon http://alicebob.cryptoland.net/closure-gotcha-with-python/#comment-311 Alex Marandon Thu, 23 Jun 2011 13:57:26 +0000 http://alicebob.cryptoland.net/?p=15#comment-311 I bumped into this gotcha today and your post gives me a clear, well written explanation. The "closure factory" solution is quite straightforward. But I wouldn't have thought of the keyword arguments workaround, which is concise but a bit cryptic. The kind of thing I'd leave a comment for in my code. It's kind of funny how one common gotcha (how default values are being evaluated) can be used as a workaround for another gotcha. I bumped into this gotcha today and your post gives me a clear, well written explanation.

The “closure factory” solution is quite straightforward. But I wouldn’t have thought of the keyword arguments workaround, which is concise but a bit cryptic. The kind of thing I’d leave a comment for in my code.

It’s kind of funny how one common gotcha (how default values are being evaluated) can be used as a workaround for another gotcha.

]]> Comment on The Frobenius endomorphism with finite fields by Yang Li http://alicebob.cryptoland.net/the-frobenius-endomorphism-with-finite-fields/#comment-102 Yang Li Mon, 08 Nov 2010 13:46:05 +0000 http://alicebob.cryptoland.net/?p=153#comment-102 Your blog helps a lot. I've been confused with Frobenius endomorphism with quadratic extension for two days. Thank you!(from China) Your blog helps a lot. I’ve been confused with Frobenius endomorphism with quadratic extension for two days.
Thank you!(from China)

]]> Comment on Access violation errors with callbacks in ctypes by Daniel G http://alicebob.cryptoland.net/access-violation-errors-with-callbacks-in-ctypes/#comment-80 Daniel G Mon, 23 Aug 2010 19:24:54 +0000 http://alicebob.cryptoland.net/?p=49#comment-80 Thanks for keeping me from going crazy -- very useful! Makes me remember how frustrating programming before google used to be :) Thanks for keeping me from going crazy — very useful! Makes me remember how frustrating programming before google used to be :)

]]> Comment on Access violation errors with callbacks in ctypes by kpoman http://alicebob.cryptoland.net/access-violation-errors-with-callbacks-in-ctypes/#comment-10 kpoman Mon, 26 Jul 2010 22:34:23 +0000 http://alicebob.cryptoland.net/?p=49#comment-10 Thank you for this post ! I also solved my bug ! It was also working on 2.5 but stopped working on 2.6. I think it is stricter in garbage collection. Keeping a global or instance reference to the callback solves the problem. Thank you, Thank you for this post ! I also solved my bug ! It was also working on 2.5 but stopped working on 2.6. I think it is stricter in garbage collection. Keeping a global or instance reference to the callback solves the problem.

Thank you,

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