How To Write A Code To A Powerbook

(1)

ICT Cubes Decode Webservice:

From Slat Sequences to Cleartext

Georg B¨ocherer and Sebastian Baur

Institute for Communications Engineering, TU Munich

georg.boecherer@tum.de,baursebastian@mytum.de

AG Kommunikationstheorie

Institute for Theoretical Information Technology RWTH Aachen University

June 21, 2013

(2)

(3)

Slats

Three types of slats: left, right, middle Purpose:

Make stacked floors appear as a cube Keep building from heating up in the sun Side effect:

Slats shadow the rooms

(4)

Design constraints

Sequence of slats should look random Balance between cooling and shadowing: 40% left, 40% right, 20% middle

(5)

Idea: Write a text to the facade

Challenge:

Find a code that maps a text to a sequence of slats The generated slat sequence should respect the design constraints

(6)

Tool 1: Data compression

Compressing (zip,rar,...) data generates a binary sequence that resembles the output of flipping a coin

(7)

Tool 2: Distribution matching

Distribution matching maps the output of flipping a coin to a sequence that resembles the output of a desired source.1

1

G. B¨ocherer,Capacity-achieving probabilistic shaping for noisy and noiseless channels, Ph.D. dissertation, RWTH Aachen University, 2012.

(8)

Tool 3: Law of large numbers

Think of a source that generates slats with the probabilities Pr(left) = Pr(right) = 0.4, Pr(middle) = 0.2

For a long sequence of slats generated by this source, the empirical distribution is close to 40% left, 40% right, 20% middle.

(9)

Approach

Text

Compression

Matching

binary sequence

slat sequence

9/1

(10)

Text: Quotes from researchers

shannonthe fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point platolet no one ignorant of mathematics enter hereschottkyspace permits only an approximate statement of the theorynyquistwhen the output of an amplifier is connected to the input through a transducer the resulting combination may be either stable or unstablehammingit is better to do the right problem the wrong way than the wrong problem the right wayturing machines take me by surprise with great frequencyfourierthe profound study of nature is the most fertile source of mathematical discoverieswienerthere are no answers only cross referencesgallagergood communication is central to a civilized societyknuthbeware of bugs in the above code i have only proved it correct not tried itmackaycombine a simple pseudo random code with a message passing decoderbellyou cannot force ideas successful ideas are the result of slow growthkolmogorovthe human brain is incapable of creating anything which is really complexgausswhen i have clarified and exhausted a subject then i turn away from it in order to go into darkness againzuseit is not true that virtually all news in a totalitarian state is falsemarconievery day sees humanity more victorious in the struggle with space and timebernoulliit would be better for the true physics if there were no mathema

(11)

Compression code

2 : 000 a : 0111 b : 101110 c : 11110 d : 00110 e : 110 f : 10000 g : 010100 h : 11111 i : 0110 j : 00111000100 k : 00111001 l : 10110 m : 01011 n : 1001 o : 1010 p : 001111 q : 00111000101 r : 0010 s : 0100 t : 1110 u : 10001 v : 0011101 w : 101111 x : 001110000 y : 010101 z : 0011100011 2

F. Altenbach, G. B¨ocherer, R. Mathar,Short Huffman codes producing 1s half of the time, presented at ICSPCS 2011.

(12)

Matching code

3 0010 : lll 1101 : llr 00000 : llm 1100 : lrl 1111 : lrr 00011 : lrm 00010 : lml 01101 : lmr 0000111 : lmm 1110 : rll 1001 : rlr 01100 : rlm 1000 : rrl 1011 : rrr 01111 : rrm 01110 : rml 01001 : rmr 000010 : rmm 01000 : mll 01011 : mlr 001101 : mlm 01010 : mrl 1010 : mrr 001100 : mrm 001111 : mml 001110 : mmr 0000110 : mmm 3

G. B¨ocherer, F. Altenbach, M. Malsbender, R. Mathar,Writing on the facade of RWTH ICT Cubes: cost constrained geometric Huffman coding, presented at ISWCS 2011, best paper award.

(13)

Checking design constraints: Cooling and shadowing

left right middle

Generated sequence 38.7% 40.9% 20.4%

Design constraint 40% 40% 20%

(14)

(15)

Reading the Facade

Two step approach:

1 Read (a part of) the slat sequence 2 Decode the slat sequence

⇒we start with step 2.4

4

Sebastian Baur: ICT Cubes Decode Webservice: Von Lamellensequenzen zu Klartext, B.Sc. thesis, TU Munich, 2013.

(16)

Synchronization Problem on Slat Level

rm z }| { rlr z }| { | {z } ’n’ 1001 rrr z }| { | {z } ’l’ 1011 mmr z }| { 0 | {z } ’a’ 0111 | {z } ’r’ 0 mll z }| { 010 |{z} ’ ’ 00 rrm z }| { 0 | {z } ’h’ 1111 rlr z }| { 1 | {z } ’d’ 001 mrr z }| { 10 | {z } ’o’ 10 rlr z }| { 10 | {z } ’i’ 01 rrr z }| { 1011 rmr z }| { | {z } ’s’ 0100 | {z } ’h’ 1 lrr z }| { 1111 | {z } ’a’ rrm z }| { 0111 | {z } ’n’ 1 mrm z }| { 001 | {z } ’n’ 100 llr z }| { 1 | {z } ’o’ 101 rmr z }| { 0 | {z } ’n’ 1001 |{z} ’ ’ lrm z }| { 000 | {z } ’t’ 11 rrr z }| { 10 | {z } ’h’ 11 lrr z }| { 111 |{z} ’e’ 1 lrr z }| { 1111

(17)

Synchronization Problem on Bit Level

rmr z }| { lrr z }| { | {z } ’c’ 1111 rrm z }| { 0 | {z } ’c’ 1111 mrm z }| { 0 | {z } ’i’ 0110 | {z } ’i’ 0 llr z }| { 110 | {z } ’o’ 1 rmr z }| { 010 | {z } ’s’ 01 lrm z }| { 00 | {z } ’a’ 011 rrr z }| { 1 | {z } ’a’ 011 lrr z }| { 1 | {z } ’c’ 111 rrl z }| { 1000 rmr z }| { | {z } ’s’ 0100 | {z } ’h’ 1 lrr z }| { 1111 | {z } ’a’ rrm z }| { 0111 | {z } ’n’ 1 mrm z }| { 001 | {z } ’n’ 100 llr z }| { 1 | {z } ’o’ 101 rmr z }| { 0 | {z } ’n’ 1001 |{z} ’ ’ lrm z }| { 000 | {z } ’t’ 11 rrr z }| { 10 | {z } ’h’ 11 lrr z }| { 111 |{z} ’e’ 1 lrr z }| { 1111 17/1

(18)

Example for Correct Decoding

rmr z }| { lrr z }| { 1111 rrm z }| { | {z } ’a’ 0111 | {z } ’n’ 1 mrm z }| { 001 | {z } ’n’ 100 llr z }| { 1 | {z } ’o’ 101 rmr z }| { 0 | {z } ’n’ 1001 lrm z }| { |{z} ’ ’ 000 | {z } ’t’ 11 rrr z }| { 10 | {z } ’h’ 11 lrr z }| { 111 |{z} ’e’ 1 rrl z }| { 1000

(19)

Observation

Slat offset periodic ⇒no automatic synchronization Bit offset aperiodic⇒ automatic synchronization

Since we want to decode very short parts of the slat sequence, we donotrely on automatic synchronization.

(20)

Approach

Let ˆt be the decoded text and suppose we have the boolean functionisSynchronized(ˆt).

forslatOffset = 0...2

for bitOffset = 0...maxLength

decode with slatOffset andbitOffset

if[isSynchronized(ˆt)] returnˆt

end if end for end for

(21)

Implementing

isSynchronized

Pilot symbols: less quotes!

Comparison with cleartext: loss of flexibility!

Dictionary

(22)

Testing Dictionary Based Synchronization

10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1 number of slats frequency of co rrect deco ding _{1. word} 1. word>1 1. & 2.(3.) word>1 adapted evaluation

(23)

Implementation

Implemented in google programming language Go Deployed in the cloud using google’s appengine

(24)

Webservice Interface

HTTP GET request Slat sequence as query:

http://ict-cubes.appspot.com/?slats=rlrrrrmmrmllrrmrlrmrrrlrrrrl Call from MATLAB:

resp=urlread(”http://ict-cubes.appspot.com/?slats=rlrrrrmmrmllrrmrlrmrrrlrrrrl”) Response as JSON string:

(25)

Outlook

Fromphototo clear text:

Make plain view of the 8 facades available to the reader Match photo to plain view

Pass slat sequence covered by photo to the webservice.