Name: David Barksdale
Member since: 2008-06-25 04:37:02
Last Login: 2012-05-27 15:48:00

Homepage: https://github.com/amatus

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Recent blog entries by amatus

My third book, Hacking Secret Ciphers with Python, is finished. It is free to download under a Creative...

My third book, Hacking Secret Ciphers with Python, is finished. It is free to download under a Creative Commons license, and available for purchase as a physical book on Amazon for $25 (which qualifies it for free shipping). This is a book that is aimed at people who have no experience programming or with cryptography. The book goes through writing Python programs that not only implement several ciphers but also programs that can hack these ciphers.

http://inventwithpython.com/blog/2013/04/15/hacking-secret-ciphers-with-python-released/

The “Invent with Python” Blog — “Hacking Secret Ciphers with Python” Released
My third book, Hacking Secret Ciphers with Python, is finished. It is free to download under a Creative Commons license, and available for purchase as a physical book on Amazon for $25 (which qualifie...

Syndicated 2013-07-26 13:41:35 from David Barksdale - Google+ Posts

Why $92,233,720,368,547,800? In binary that's 101000111101011100001010001111010111000010100011111011000...

Why $92,233,720,368,547,800?
In binary that's 101000111101011100001010001111010111000010100011111011000. That's a 20-bit pattern that almost repeats 3 times. If we add three leading zeroes we get a nice even 60 bits and the boundaries of the pattern can be shifted without any trouble, then fix the last 7 bits to fit the pattern we get 92,233,720,368,547,758. Was this the actual sum and it got rounded before being reported by BBC? Maybe Mr. Reynolds had the extra $42 already in his account. What does this 20-bit pattern mean? 10100011110101110000
Let's try IEEE floating point format. In binary scientific notation the number is 2^56 * 1.01000111101011100001010001111010111000010100011111011_2. The mantissa is one bit too long to fit in the double-precision format. If we truncate that bit our new number is 92,233,720,368,547,790 and the binary representation is 0100001101110100011110101110000101000111101011100001010001111101. The exponent doesn't follow the nice pattern we have in the mantissa and no sane person would store monetary values in a lossy format like this, so this looks like a dead-end.
Back to the 20-bit pattern. We could Google search all 20 rotations of this pattern for clues, but the very first search turns up a plausible result. This pattern is the repeating bits of the binary expansion of 1/100 and would appear in the floating point representation. This suggests that somewhere in PayPal's code, one penny turned into $92 quadrillion because a floating point number was interpreted as an integer. If only my bank's software would make the same mistake.

PayPal in $92 quadrillion error

Syndicated 2013-07-18 14:24:12 from David Barksdale - Google+ Posts

I've been asked several times for links to various #GNUnet  papers. Here they are in somewhat chronological...

I've been asked several times for links to various #GNUnet  papers. Here they are in somewhat chronological order.

An Encoding for Censorship-Resistant Sharing: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.81.6369&rep=rep1&type=pdf

gap - Practical Anonymous Networking: http://grothoff.org/christian/aff.pdf

An Excess-Based Economic Model for Resource Allocation in Peer-to-Peer Networks: http://grothoff.org/christian/ebe.pdf

Bootstrapping of Peer-to-Peer Networks: http://grothoff.org/christian/bootstrap.pdf

R5N : Randomized Recursive Routing for Restricted-Route Networks: https://gnunet.org/sites/default/files/nss2011.pdf

Efficient and Secure Decentralized Network Size Estimation: https://gnunet.org/sites/default/files/nse-techreport.pdf

Design and Implementation of a Censorship Resistant and Fully Decentralized Name System: https://gnunet.org/sites/default/files/schanzen2012msc.pdf

Decentralized Evaluation of Regular Expressions for Capability Discovery in Peer-to-Peer Networks: https://gnunet.org/sites/default/files/szengel2012ms.pdf

Syndicated 2013-06-28 03:31:27 from David Barksdale - Google+ Posts

Yet another thing #google  is doing to make my life as a #ejabberd  operator unpleasant. I can't talk...

Yet another thing #google  is doing to make my life as a #ejabberd  operator unpleasant. I can't talk to any new gtalk users because I can't send presence subscription requests to them!

[Operators] Spammy invites

Syndicated 2013-03-05 19:58:32 from David Barksdale - Google+ Posts

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