lab06 by typing:
mkdir lab06Change to this directory by typing:
cd lab06
WWII code-breaking at Bletchley Park was the genesis of modern computing. In this lab you too will perform computer-assisted code-breaking but don't worry the ciphers you must break are simpler than the Nazi's Lorenz and Enigma ciphers.
The exercises in the labs require you to read characters. Use the library function getchar to do this.
getchar reads the next character from standard input and returns it.
If getchar is unable to read a character it return the special value EOF.
When input is coming from a file, getchar will return EOF
after the last character in the file is read.
When input is coming from a (Linux/OSX) terminal, you can indicate no more characters
can be read by typing Ctrl+D.
This will cause getchar to return EOF
In some of this week's lab exercises you will find it convenient to put the test input in a file, rather than type it every time you want to test the program.
You can use a < character to indicate to the shell that you want to run a program taking its input from a file.
So for example you might create the file input.txt with gedit and
then run a.out takes its input from the file rather the terminal:
gedit input.txt & ./a.out <input.txt
devowel.c which reads characters from its input
and writes the same characters to its output, except it does not write lower case vowels ('a', 'e','i', 'o', 'u').
Your program should stop only at the end of input.
For example:
./devowel Are you saying 'Boo' or 'Boo-Urns'? Ar y syng 'B' r 'B-Urns'? In this house, we obey the laws of thermodynamics! In ths hs, w by th lws f thrmdynmcs!Hint: hint use
getcharto read characters (don't use scanf or fgets).
Hint: you need only a single int variable. Don't use an array.
Hint: use putchar to output each character.
Hint: make sure you understand this example program which reads characters until end of input.
Hint: make sure you understand this example program which reads characters, printing them with lower case letters converted to upper case.
Hint: create a function with a prototype like this:
int is_vowel(int character);which returns 1 the character is a lower case vowel and 0 otherwise.
Hint: To tell the program you have finished typing, you can press Ctrl+D.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest devowel
give cs1511 wk06_devowel devowel.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
swap_case.c which reads characters from its input
and writes the same characters to its output with lower case letters converted to upper case
and upper case letters converted to lower case.
Your program should stop only at the end of input.
For example:
dcc swap_case.c -o swap_case ./swap_case Are you saying 'Boo' or 'Boo-Urns'? aRE YOU SAYING 'bOO' OR 'bOO-uRNS'? In this house, we obey the laws of thermodynamics! iN THIS HOUSE, WE OBEY THE LAWS OF THERMODYNAMICS! UPPER !@#$% lower upper !@#$% LOWERHint: hint use
getcharto read characters (don't use scanf or fgets).
Hint: you need only a single int variable. Don't use an array.
Hint: use putchar to output each character.
Hint: make sure you understand this example program which reads characters until end of input.
Hint: make sure you understand this example program which reads characters, printing them with lower case letters converted to upper case.
Hint: create a function with a prototype like this:
int swap_case(int character);which:
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest swap_case
give cs1511 wk06_swap_case swap_case.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
caesar.c which reads characters from its input
and writes the characters to its output encrypted with a Caesar cipher.
A Caesar cipher shifts each letter a certain number of positions in the alphabet.
The number of positions to shift will be given to your program as a command line argument.
Characters other than letters should not be encrypted.
Your program should stop only at the end of input.
Your program should contain at least one function other than main.
For example:
./caesar 1 This life well it's slipping right through my hands Uijt mjgf xfmm ju't tmjqqjoh sjhiu uispvhi nz iboet These days turned out nothing like I had planned Uiftf ebzt uvsofe pvu opuijoh mjlf J ibe qmboofe ./caesar 10 abcdefghijklmnopqrstuvwxyz klmnopqrstuvwxyzabcdefghij ABCDEFGHIJKLMNOPQRSTUVWXYZ KLMNOPQRSTUVWXYZABCDEFGHIJ ./caesar -42 Control well it's slipping right through my hands Myxdbyv govv sd'c cvszzsxq bsqrd drbyeqr wi rkxnc These days? Droco nkic?Hint: handle upper and lower case letters separately
Hint: use %
Hint: use atoi to convert the first command-line argument to an int.
Hint:make sure you understand this example program which uses a atoi to convert command-line arguments to an ints.
Hint: create a function with a prototype like this:
int encrypt(int character, int shift);which returns the character shifted by the specified amount
Z uf dp drbvlg ze jfdvsfup vcjv'j tri Nv fiuvi uzwwvivek uizebj rk kyv jrdv srij Z befn rsflk nyrk pfl uzu reu Z nreer jtivrd kyv kilky Jyv kyzebj pfl cfmv kyv svrty, pfl'iv jlty r urde czriUse the program you have just written to discover the secret text?
Hint:: try different shifts until you see English.
You program will only be tested with an appropriate command line argument - but a good programmer would check the command line argument is present and appropriate.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest caesar
give cs1511 wk06_caesar caesar.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
frequency_analysis.c which reads characters from its input
until end of input.
It should then print the occurrence frequency for each of the 26 letters 'a'..'z'.
The frequency should be printed as a decimal value and an absolute number in exactly the format below.
Note upper and lower case letters are counted together.
For example:
./frequency_analysis Hello and goodbye. 'a' 0.066667 1 'b' 0.066667 1 'c' 0.000000 0 'd' 0.133333 2 'e' 0.133333 2 'f' 0.000000 0 'g' 0.066667 1 'h' 0.066667 1 'i' 0.000000 0 'j' 0.000000 0 'k' 0.000000 0 'l' 0.133333 2 'm' 0.000000 0 'n' 0.066667 1 'o' 0.200000 3 'p' 0.000000 0 'q' 0.000000 0 'r' 0.000000 0 's' 0.000000 0 't' 0.000000 0 'u' 0.000000 0 'v' 0.000000 0 'w' 0.000000 0 'x' 0.000000 0 'y' 0.066667 1 'z' 0.000000 0 ./frequency_analysis Hey! Hey! Hey! I don't like walking around this old and empty house So hold my hand, I'll walk with you my dear 'a' 0.072289 6 'b' 0.000000 0 'c' 0.000000 0 'd' 0.084337 7 'e' 0.084337 7 'f' 0.000000 0 'g' 0.012048 1 'h' 0.096386 8 'i' 0.072289 6 'j' 0.000000 0 'k' 0.036145 3 'l' 0.084337 7 'm' 0.036145 3 'n' 0.060241 5 'o' 0.084337 7 'p' 0.012048 1 'q' 0.000000 0 'r' 0.024096 2 's' 0.036145 3 't' 0.048193 4 'u' 0.036145 3 'v' 0.000000 0 'w' 0.036145 3 'x' 0.000000 0 'y' 0.084337 7 'z' 0.000000 0Hint: hint use
getcharto read characters (don't use scanf or fgets).
Hint: make sure you understand this example program which reads characters until end of input.
Hint: use an array to store counts of each letter.
Hint: make sure you understand this example program which counts integers from the range 0..99.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest frequency_analysis
give cs1511 wk06_frequency_analysis frequency_analysis.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
A Substitution cipher maps each letter to another letter.
The mapping will be given to your program as a single command line argument. This command line argument will contain 26 characters: an ordering of the letters 'a'..'z'.
Characters other than letters should not be encrypted.
Your program should stop only at the end of input.
Your program should contain at least one function other than main.
For example:
./substitution qwertyuiopasdfghjklzxcvbnm I was scared of dentists and the dark O vql leqktr gy rtfzolzl qfr zit rqka I was scared of pretty girls and starting conversations O vql leqktr gy hktzzn uoksl qfr lzqkzofu egfctklqzogfl ./substitution abcdefghijklmnopqrstuvwxyz The identity cipher!!! The identity cipher!!! ./substitution bcdefghijklmnopqrstuvwxyza The Caesar cipher is a subset of the substitution cipher! Uif Dbftbs djqifs jt b tvctfu pg uif tvctujuvujpo djqifs!Your program will only be tested with an appropriate command line argument - but a good programmer would check the command line argument is present and appropriate.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest substitution
give cs1511 wk06_substitution substitution.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
For example:
./decode qwertyuiopasdfghjklzxcvbnm O vql leqktr gy rtfzolzl qfr zit rqka I was scared of dentists and the dark O vql leqktr gy hktzzn uoksl qfr lzqkzofu egfctklqzogfl I was scared of pretty girls and starting conversations ./decode abcdefghijklmnopqrstuvwxyz The identity cipher!!! The identity cipher!!! ./decode bcdefghijklmnopqrstuvwxyza Uif Dbftbs djqifs jt b tvctfu pg uif tvctujuvujpo djqifs! The Caesar cipher is a subset of the substitution cipher!Your program will only be tested with an appropriate command line argument - but a good programmer would check the command line argument is present and appropriate.
Di jd, vdl'ht xtqa dh O qn Vdl rdlwk O'ss wdkith htqromu omkd ok O fhdwqwsv xdm'k Styk kd nv dxm rtzoetj Wlk kiqk'j kit royythtmet om dlh dfomodmj Vdl'ht q ndlkiyls Kiqk qndlmkj ydh qmdkith xtta dm nv dxm Mdx O'n q mdzts nqrt htjdlhetyls O jkqhk q eiqom xoki nv kidluik Kqsa oj eitqf, nv rqhsomu Xitm vdl'ht yttsomu houik qk idnt O xqmmq nqat vdl ndzt xoki edmyortmet O xqmmq wt xoki vdl qsdmtWhat was the original text?
Hint: use frequency_analysis.c on the encrypted text and compare the frequencies to English letter frequencies and then try your guesses with decode.c
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest decode
give cs1511 wk06_decode decode.cNote, even though this is a pair exercise, you both must run give from your own account before Tuesday 17 April 23:59:59 to obtain the marks for this lab exercise.
Your program should make no assumptions about the language of the original text - don't assume its English. However, you can assume the English alphabet ('a'..'z').
Your program will be given as a command-line argument the name of a file containing a large amount of unencrypted text in the same language as the encrypted text.
For example for example your program might be given this file containing 188k characters of English text (wikipedia sentences from here)
Your program will be given the encrypted text on standard input. It should print its decryption.
For example, here is some English text encrypted with a Caesar cipher with an unknown shift:
Kyzj zj fli crjk xffuspv Z yrkv kf wvvc kyv cfmv svknvve lj uzv Slk zk'j fmvi Aljk yvri kyzj reu kyve Z'cc xf Pfl xrmv dv dfiv kf czmv wfi Dfiv kyre pfl'cc vmvi befnSo for example:
./crack_caesar wiki_sentences.txt Kyzj zj fli crjk xffuspv Z yrkv kf wvvc kyv cfmv svknvve lj uzv Slk zk'j fmvi Aljk yvri kyzj reu kyve Z'cc xf Pfl xrmv dv dfiv kf czmv wfi Dfiv kyre pfl'cc vmvi befn This is our last goodbye I hate to feel the love between us die But it's over Just hear this and then I'll go You gave me more to live for More than you'll ever knowYou may assume the encrypted text of stdin contains at most 10000 characters.
You may assume the unencrypted example text in the file contains at most 250000 characters.
Hint: use fopen to open the file and fgetc to read the file. If you haven't seen them in lectures yet, read this example program to see how to use this functions to read a file.
Hint: read all the encrypted text into an array, then decrypt it.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest crack_caesar
give cs1511 wk06_crack_caesar crack_caesar.cYou must run give before Friday 20 April 23:59:59 to obtain the marks for this lab exercise. Note, this is an individual exercise, the work you submit with give must be entirely your own.
Your program should make no assumptions about the language of the original text - don't assume its English. In other words don't hard code English properties into your program, extract the statistical properties from the sample plain text. However, you can assume the English alphabet ('a'..'z').
Your program will be given as a command-line argument the name of a file containing a large amount of unencrypted text in the same language as the encrypted text.
Your program will be given the encrypted text on standard input. You may read it all before printing the decryption.
For example:
./crack_substitution wiki_sentences.txt M'ka paat dra qegbu, ueta md xbb Rxu vw fxya teq Umxvetup, ogmbbmxtd, mt Oab-Xmg teq Red psvvag tmlrdp, vmu Jsbw Qrat wes xtu M qaga negakag qmbu Dra fgxzw uxwp, fmdw bmlrdp Dra qxw wes'u cbxw qmdr va bmya x frmbu Qmbb wes pdmbb beka va Qrat M'v te betlag westl xtu oaxsdmnsb? Qmbb wes pdmbb beka va Qrat M'ka led tedrmtl osd vw xfrmtl pesb? M yteq wes qmbb, M yteq wes qmbb M yteq drxd wes qmbb Qmbb wes pdmbb beka va qrat M'v te betlag oaxsdmnsb? M'ka paat dra qegbu, bmd md sc Xp vw pdxla teq Frxbbatlmtl xtlabp mt x taq xla teq Red psvvag uxwp, gefy t gebb Dra qxw wes cbxw neg va xd wesg preq Xtu xbb dra qxwp, M led de yteq Wesg cgaddw nxfa xtu abafdgmf pesb I've seen the world, done it all Had my cake now Diamonds, brilliant, in Bel-Air now Hot summer nights, mid July When you and I were forever wild The crazy days, city lights The way you'd play with me like a child Will you still love me When I'm no longer young and beautiful? Will you still love me When I've got nothing but my aching soul? I know you will, I know you will I know that you will Will you still love me when I'm no longer beautiful? I've seen the world, lit it up As my stage now Challenging angels in a new age now Hot summer days, rock n roll The way you play for me at your show And all the ways, I got to know Your pretty face and electric soulYou may assume the encrypted text on stdin contains at most 10000 characters.
You may assume the unencrypted example text in the file contains at most 250000 characters.
Hint: you will need to look at the probabilities of sequences of 2 or perhaps 3 letters occurring or perhaps the probabilities of words.
An autotest is available to help you test your program but because this is a difficult problem it is possible very good attempts at the problem won't pass the autotests.
When you think your program is working you can use autotest to run some simple automated tests:
1511 autotest crack_substitution
give cs1511 wk06_crack_substitution crack_substitution.cYou must run give before Friday 20 April 23:59:59 to obtain the marks for this lab exercise. Note, this is an individual exercise, the work you submit with give must be entirely your own.
You can run give multiple times. Only your last submission will be marked.
Don't submit any exercises you haven't attempted.
If you are working at home, you may find it more convenient to upload your work via give's web interface.
Remember you have until Tuesday 17 April 23:59:59 to submit your work.
Automarking will be run several days after the submission deadline for the test. When complete you can view automarking here and you can view the the resulting mark via give's web interface
You can read more about lab assessment here