Andrew Cooke | Contents | Latest | RSS | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Choochoo Training Diary

Last 100 entries

[Programming] React Leaflet; AliExpress Independent Sellers; Applebaum - Twilight of Democracy; [Politics] Back + US Elections; [Programming,Exercise] Simple Timer Script; [News] 2019: The year revolt went global; [Politics] The world's most-surveilled cities; [Bike] Hope Freehub; [Restaurant] Mama Chau's (Chinese, Providencia); [Politics] Brexit Podcast; [Diary] Pneumonia; [Politics] Britain's Reichstag Fire moment; install cairo; [Programming] GCC Sanitizer Flags; [GPU, Programming] Per-Thread Program Counters; My Bike Accident - Looking Back One Year; [Python] Geographic heights are incredibly easy!; [Cooking] Cookie Recipe; Efficient, Simple, Directed Maximisation of Noisy Function; And for argparse; Bash Completion in Python; [Computing] Configuring Github Jekyll Locally; [Maths, Link] The Napkin Project; You can Masquerade in Firewalld; [Bike] Servicing Budget (Spring) Forks; [Crypto] CIA Internet Comms Failure; [Python] Cute Rate Limiting API; [Causality] Judea Pearl Lecture; [Security, Computing] Chinese Hardware Hack Of Supermicro Boards; SQLAlchemy Joined Table Inheritance and Delete Cascade; [Translation] The Club; [Computing] Super Potato Bruh; [Computing] Extending Jupyter; Further HRM Details; [Computing, Bike] Activities in ch2; [Books, Link] Modern Japanese Lit; What ended up there; [Link, Book] Logic Book; Update - Garmin Express / Connect; Garmin Forerunner 35 v 230; [Link, Politics, Internet] Government Trolls; [Link, Politics] Why identity politics benefits the right more than the left; SSH Forwarding; A Specification For Repeating Events; A Fight for the Soul of Science; [Science, Book, Link] Lost In Math; OpenSuse Leap 15 Network Fixes; Update; [Book] Galileo's Middle Finger; [Bike] Chinese Carbon Rims; [Bike] Servicing Shimano XT Front Hub HB-M8010; [Bike] Aliexpress Cycling Tops; [Computing] Change to ssh handling of multiple identities?; [Bike] Endura Hummvee Lite II; [Computing] Marble Based Logic; [Link, Politics] Sanity Check For Nuclear Launch; [Link, Science] Entropy and Life; [Link, Bike] Cheap Cycling Jerseys; [Link, Music] Music To Steal 2017; [Link, Future] Simulated Brain Drives Robot; [Link, Computing] Learned Index Structures; Solo Air Equalization; Update: Higher Pressures; Psychology; [Bike] Exercise And Fuel; Continental Race King 2.2; Removing Lowers; Mnesiacs; [Maths, Link] Dividing By Zero; [Book, Review] Ray Monk - Ludwig Wittgenstein: The Duty Of Genius; [Link, Bike, Computing] Evolving Lacing Patterns; [Jam] Strawberry and Orange Jam; [Chile, Privacy] Biometric Check During Mail Delivery; [Link, Chile, Spanish] Article on the Chilean Drought; [Bike] Extended Gear Ratios, Shimano XT M8000 (24/36 Chainring); [Link, Politics, USA] The Future Of American Democracy; Mass Hysteria; [Review, Books, Links] Kazuo Ishiguro - Never Let Me Go; [Link, Books] David Mitchell's Favourite Japanese Fiction; [Link, Bike] Rear Suspension Geometry; [Link, Cycling, Art] Strava Artwork; [Link, Computing] Useful gcc flags; [Link] Voynich Manuscript Decoded; [Bike] Notes on Servicing Suspension Forks; [Links, Computing] Snap, Flatpack, Appimage; [Link, Computing] Oracle is leaving Java (to die); [Link, Politics] Cubans + Ultrasonics; [Book, Link] Laurent Binet; VirtualBox; [Book, Link] No One's Ways; [Link] The Biggest Problem For Cyclists Is Bad Driving; [Computing] Doxygen, Sphinx, Breathe; [Admin] Brokw Recent Permalinks; [Bike, Chile] Buying Bearings in Santiago; [Computing, Opensuse] Upgrading to 42.3; [Link, Physics] First Support for a Physics Theory of Life; [Link, Bike] Peruvian Frame Maker; [Link] Awesome Game Theory Tit-For-Tat Thing; [Food, Review] La Fabbrica - Good Italian Food In Santiago; [Link, Programming] MySQL UTF8 Broken; [Link, Books] Latin American Authors

© 2006-2017 Andrew Cooke (site) / post authors (content).

Amazing Julia RC5 Code Parameterized By Word Size

From: andrew cooke <andrew@...>

Date: Wed, 13 Nov 2013 21:34:38 -0300

The RC5 cipher is actually a whole family of related algorithms.  It has a
variable number of rounds, variable key length and, strangest of all, can work
with different sized words.

So there's an 8 bit RC5, a 16 bit RC5, a 32 bit RC5, and a 64 bit RC5.  Those
are common because they match common hardware, but there's nothing stopping
you have a 23 bit RC5 if you really want.

(By the way, the paper defining all this is very clear - see
http://people.csail.mit.edu/rivest/Rivest-rc5.pdf)


So how do you write an implementation without repeating yourself?  Well, of
course, a "real" implementation would be hand-coded C and assembly for speed.
But I wanted a version I could hack (in particular, remove or modify
rotations) so I needed to write my own.  And it turns out that Julia makes it
incredibly easy to implement the common (8,16,32,64) sizes "all at once".

Here, for example, is the encryption for a block (two words):

  function encrypt{W<:Unsigned}(s::State{W}, a::W, b::W)
      a::W = a + s.s[1]
      b::W = b + s.s[2]
      for i = 1:s.r
	  a = rotatel(s.w, a $ b, b) + s.s[2i+1]
	  b = rotatel(s.w, a $ b, a) + s.s[2i+2]
      end
      a, b
  end

The W there can be Uint8, Uint16, Uint32 or Uint64 - and whichever it is, the
code will do the right thing.

For another example, here's the structure that defines the cipher state:

  immutable type State{W<:Unsigned}
      w::Type{W}
      r::Uint8
      k::Array{Uint8}
      s::Array{W}
  end

Note how simple it is to parameterize things by type, and even to store a type
in the structure for easy reference later (as I write this it strikes me that
maybe that should also be available through introspection - I need to check).

More code (some bits are just a little bit uglier) here -
https://github.com/andrewcooke/BlockCipherSelfStudy.jl/blob/master/src/RC5.jl

Andrew

Comment on this post