Main Program
% Secret service encryption system's driver program
clear
fprintf('Secret Service System\n\n')
format compact
choice = input('Enter 1 to encrypt, 2 to decrypt: ');
while (choice ~= 1 & choice ~= 2)
choice = input('Invalid input. Enter 1 to encrypt, 2 to decrypt: ');
end
% Get input file
% In the input statement, using the extra parameter 's' means
% the user does NOT enclose the input string in single quotes
disp(' ')
inFile = input('Enter input filename: ', 's');
message = readtext(inFile)
% Get key sentence and construct the key
disp(' ')
sentence = input('Input key sentence: ', 's');
key = makeKey(sentence)
% Encrypt or decrypt message
disp(' ')
if (choice == 1)
newMessage = encode(key, message)
else
newMessage = decode(key, message)
end
% One should get rid of the evidence using the statement below, but
% de-bugging is easier if the variables survive...
% clear sentence key message newMessage inFile outFile
Readtext function (you don’t need to understand the detail here)
function result = readtext(filename)
% Function readtext reads an ascii text file
% Input: name of a text file with equal number of characters in each column
% Output: a MATLAB array containing all characters in the input file
fid = fopen(filename);
if (fid < 0)
message = sprintf('File %s cannot be opened.\nMake sure that file %s exists in
your working directory.',...
filename, filename)
error(message)
end
i = 1;
line = fgetl(fid);
text = line;
while (~feof(fid))
line = fgetl(fid);
text = [text; line];
i=i+1;
end
result = text;
MakeKey and helpers
function res = makeKey(sent)
%This function creates the key for the encryption algorithm.
key = [' ']
j=0;
for k = 1:length(sent)
%make sure we have a char and it is not already in the array
if isletter(sent(k)) & ~inArray(key, sent(k))
key(floor(j/6) + 1, mod(j,6)+1) = upper(sent(k));
j = j +1;
end
end
for k = 0:25
%make sure we have a char and it is not already in the array
if ~inArray(key, char('A' + k))
key(floor(j/6) + 1, mod(j,6)+1) = 'A' + k;
j = j +1;
end
end
% add spaces to the array
key(5,3:6) = ' '
res = key
function res = inArray( key, symbol)
%this function returns 1 if the char symbol is present in the array key
res = sum(sum(key == upper(symbol)));
Encode and helpers
function res = encode(key, text)
%Given a key and text in a nxm array, this function returns the encrypted text
%in a nx2m array
encr = [' ']
[h,w] = size(text)
for k = 1:h
for j = 1:w
if (isletter(text(k,j)) | text(k,j) == ' ')
twoLetters = findEncr(key, text(k,j));
encr(k, 2*j - 1:2*j) = twoLetters;
else
encr(k, 2*j - 1:2*j) = text(k,j);
end
end
end
res = encr
function res = findEncr(key, symbol)
%given a key and a char, this function returns R and C, the characters first in
the %corresponding
%row and column, respectively of the key symbol
[x, y] = size(key);
[r, c] = find(key == upper(symbol));
res = [key(r(1),1), key(1,c(1))];
Decode and helpers
function res = decode(key, text)
%Given a key and text in a nxm array, this function returns the decrypted text
% in a nxm/2 array
decr = [' ']
[h,w] = size(text)
for k = 1:h
for j = 1:(w/2)
decr(k,j) = findDecr(key, text(k,2*j - 1:2*j));
end
end
res = decr
function res = findDecr(key, symbols)
%given a key and a char, this function returns R and C, the characters first
%in the corresponding row and column, respectively of the key
[x, y] = size(key);
found = 0;
k = 1;
j = 1;
%This part could be done with find as well
%Done using max for illustrative purposes
[max1, k] = max(key(1:x,1) == symbols(1));
[max2, j] = max(key(1,1:y) == symbols(2));
if (max1 == 0 | max2 == 0)
res = symbols(1);
else
res = key(k,j);
end
1.
>> encrSystem
Secret Service System
Enter 1 to encrypt, 2 to decrypt: 1
Enter input filename: textline.txt
message =
Write & test each function independently!
Input key sentence: Show variable values to help debug
key =
SHOWVA
RIBLEU
TPDGCF
JKMNQX
YZ
newMessage =
SWRSRHTSRVYO&&YOTSRVSSTSYORVSATVSHYOTARAJWTVTSRHSOJWYORHJWTORVTHRVJWTORVJWTSRWYS!!
2.
>> encrSystem
Secret Service System
Enter 1 to encrypt, 2 to decrypt: 2
Enter input filename: codeline.txt
message =
SWRSRHTSRVYO&&YOTSRVSSTSYORVSATVSHYOTARAJWTVTSRHSOJWYORHJWTORVTHRVJWTORVJWTSRWYS!!
Input key sentence: Show variable values to help debug
key =
SHOWVA
RIBLEU
TPDGCF
JKMNQX
YZ
newMessage =
WRITE & TEST EACH FUNCTION INDEPENDENTLY!
3.
>> encrSystem
Secret Service System
Enter 1 to encrypt, 2 to decrypt: 2
Enter input filename: secret.txt
message =
JMVNVMSASSVMWMSSVMSNBMWMSMVMWMSASNWMSASSVYSOSNWMSMSAJNVYVOSNWMBMBSWMVOVOVO,,WMBMJNSAWSSNWMBAJNSOSMWMVYBYVMWMSSVM
JNVSVOBOVM''SSWMBOSAJNWMJMSOSOVN
WM[[BNWM77]]..WMVOVYWMSSBYSOJYVNBMWMBSVMWMBSSAVYVYVNVMSSBYVOJMWMBNJNVMSYWMVOSNWMBOSOVNSOJN,,WMSASNBMWMSSVYSASNBM
SAJNBM,,WMBSJYVYWMWSVOVYBYWMWMWM
BOVMJNVYSAVOSNWMVMWOVYJNSASSWMVOSNBOVNJYBMVOSNBN::WMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWM
WMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWM
11))WMSSWSVOVYBOBYVMSSWMVYSOWMSAVNVYVMJNWMVYBYVMWMVYSYJMVMWMSASNBMWMBOSOVNSOJNWMSOBAWMBAJNSOSNVYWMSASNBMWMJNVMSA
JNWMVNVOBNBYVYSS..WMWMWMWMWMWMWM
22))WMJNVMVOSNBASOJNBOVMBMWMSSVYVMVMVNWMBSJYSMJMVMJNSS,,WMBASOJNVMWMSASNBMWMSABAVY,,WMVOSNWMBOSASSVMWMVOWMSNVMVM
BMWMVYSOWMJNSASMWM((BAVMWSWMWMWM
JMVMSOJMVNVMWMJOSNSOWSWMBYSOWSWMVYSOWMJNVMBOSOBNSNVOVAVMWMJNVMVOSNBASOJNBOVMBMWMSSVYVMVMVN..))WMWMWMWMWMWMWMWMWM
WMWMWMWMWMWMWMWMWMWMWMWMWMWMWMWM
33))WMSAWMJNSABMVOSOWMJMVOBOJOWMJYJMWMVYJYSNVMBMWMVYSOWMJNVMBOVMVOVSVMWMVYBYVMWMSAJMJMSAJNSAVYJYSSWMBOSAVNVNVMBM
WMVYBYVMWMBYSOSMVMJN..WMVYBYVMWM
VNSAVYVYVMJNWMVOSSWMVYBYVMWMSMVOBMBNVMVYWMVYJNSASNSSSMVOVYVYVMJNWMVYBYSAVYWMSYSOJYWMSSVMSNVYWMSMVMWMWSBYVOBOBY,,
WMJMJNVOVSVOVNSYWMWMWMWMWMWMWMWM
VOSNSSVYSAVNVNVMBMWMVOSNWMSASNWMVMSNVMSMSY''SSWMBOSAJN,,WMSAVNVNSOWSSSWMSMVMWMVYSOWMBASOVNVNSOWSWMBYVOSMWMWSVOVY
BYSOJYVYWMBMVOBABAVOBOJYVNVYSY..
Input key sentence: so many movies zo little time
key =
SOMANY
VIEZLT
BCDFGH
JKPQRU
WX
newMessage =
PLEASE SEND ME AN ASTON MARTIN DB III, DRAWN FROM THE SERVICE'S CAR POOL
[G 7]. IT SHOULD BE BATTLESHIP GREY IN COLOR, AND STANDARD, BUT WITH
CERTAIN EXTRAS INCLUDING:
1) SWITCHES TO ALTER THE TYPE AND COLOR OF FRONT AND REAR LIGHTS.
2) REINFORCED STEEL BUMPERS, FORE AND AFT, IN CASE I NEED TO RAM (FEW
PEOPLE KNOW HOW TO RECOGNIZE REINFORCED STEEL.)
3) A RADIO PICK UP TUNED TO RECEIVE THE APPARATUS CALLED THE HOMER. THE
LATTER IS THE MIDGET TRANSMITTER THAT YOU SENT ME WHICH, PRIVILY
INSTALLED IN AN ENEMY'S CAR, ALLOWS ME TO FOLLOW HIM WITHOUT DIFFICULTY.