Which set of letters spells a valid word when decrypted using the caesar cipher with a key of 2?

from string import ascii_lowercase as alphabet

class CaesarCypher:
    alpha_len = len(alphabet)
    min_guess_rate = 0.2

Encryption and decryption is a same stuff. when you want to decrypt for example with shift 10 that means that you can encrypt it with shift 26 - 10. In this case cycle will repeat at if you going to shift whole alphabet it will be the same. Also here i've proceed upper case and non chars

    def __call__(self, text, offset, encrypt=True):
        if not encrypt:
            offset = self.alpha_len - offset
        result = []
        for letter in text:
            if not letter.isalpha():
                result.append(letter)
                continue
            letter_to_process = letter.lower()
            processed_letter = self._encrypt_letter(letter_to_process, offset)
            if letter.isupper():
                processed_letter = processed_letter.upper()
            result.append(processed_letter)
        return ''.join(result)

all encryption goes here at most.

    def _encrypt_letter(self, letter, offset=0):
        position = (alphabet.find(letter) + offset) % self.alpha_len
        return alphabet[position]

this part is for broot force and guess throug dictionary frequency.

    @staticmethod
    def __how_many_do_i_know(text):
        clean_words = filter(lambda x: x.isalpha(), text.split())
        clean_words = ['\'{}\''.format(x) for x in clean_words]
        cursor = conn.cursor()
        query = 'SELECT COUNT(*) FROM mydictionary WHERE word IN ({})'.format(",".join(clean_words))
        cursor.execute(query)
        response = cursor.fetchone()[0]
        return response / len(clean_words)

    def guess_encode(self, text):
        options = [self(text, offset, encrypt=False) for offset in range(self.alpha_len)]
        best_option = [self.__how_many_do_i_know(option) for option in options]
        best_key, guess_rate = max(enumerate(best_option), key=lambda x: x[-1])
        guess_text = options[best_key]
        return best_key, guess_rate, guess_text

Caesar's cypher is the simplest encryption algorithm. It adds a fixed value to the ASCII (unicode) value of each character of a text. In other words, it shifts the characters. Decrypting a text is simply shifting it back by the same amount, that is, it substract the same value from the characters. Write a function called caesar that accepts two arguments: the first is the character vector to be encrypted, while the second is the shift amount. The function returns the output argument coded, the encrypted text. The function needs to work with all the visible ASCII characters from space to ~. The ASCII codes of these are 32 through 126. If the shifted code goes outside of this range, it should wrap around. For example, if we shift ~ by 1, the result should be space. If we shift space by -1, the result should be ~.

for the first part of the code...this works

function coded=caesar(A,n)

char_set=char(32):char(126)

coded=char(A+n);

end

But if i want to maintain the range between 32 and 126 ....and also wrap around the same values as asked in later half of question , it doesnt work

function coded=caesar(A,n)

char_set=char(32):char(126)

while A <=char_set

coded=char(A+n);

end

end

please help me with the concerned code buiding ....( expect a simple approach , since iam a begineer)

test for these outputs

caesar('ABCD',1)

ans =

'BCDE'

caesar('xyz ~',1)

ans =

'yz{! '

caesar('xyz ~',-1)

ans =

'wxy~}'

Accepted Answer

function coded = caesar(M, n)

num = double(M);

num2 = num;

N = n - 95 * fix(n/95);

for i = 1:length(num);

if num(i) + N < 32

num2(i) = 126 - (31- num(i) - N);

elseif num(i) + N > 126

num2(i) = 32 + (num(i) + N -127);

else

num2(i) = num(i) + N ;

end

coded = char(num2);

end

I spent halfhour on solving this problem, a little bit hard.

This is correct code. Hope it helps.

More Answers (38)

function coded= caesar(string,shift)

value=string+shift;

for i=1:length(value)

while value(i)<32

value(i)=value(i)+95;

end

while value(i)>126

value(i)=value(i)-95;

end

end

coded=char(value);

Thanks to a person who told about circshift function. I've been tried several hours to solve this task without that function.

So finaly I've passed all tests. And final code is much shorter and elegant as I have at today's morning ))

It has only 4 lines including the "end".

The main idea is to shift character table, but not the symbols of input.

function coded = caesar (array,shift)

shifted_array=circshift(char(32:126),-shift);

coded = shifted_array(double(array)-31)

end

function coded = caesar(text,amound)

n=amound - 95 * fix(amound/95);

v=double(text)+n;

v(v<32)=126-(31-v(v<32));

v(v>126)=32+(-127+v(v>126));

coded=char(v);

end

Use mod or rem to constrain values between 0 and a maximum, with wrap-around.e.g:

>> mod(0:51, 26)

ans =

Columns 1 through 21

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Columns 22 through 42

21 22 23 24 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Columns 43 through 52

16 17 18 19 20 21 22 23 24 25

You can see that values 26, 27, ... go back to 0, 1, ...

Add/subtract some offsets to do the same for values in the range 32:126

I came up with an approach which uses logical indexing instead of if statement

function coded=caesar(str,n)

str1=double(str);

m=n-95*floor(n/95);

codedstr1=str1+m;

codedstr1(codedstr1>=127)=codedstr1(codedstr1>=127)-127+32;

coded=char(codedstr1);

end

function coded = caesar(message , n)

msg = double(message);

m = mod(n, 95);

coded_msg = msg + m;

coded_msg(coded_msg > 126) = coded_msg(coded_msg > 126) - 95;

coded_msg(coded_msg < 32) = coded_msg(coded_msg < 32) + 95;

coded =char(coded_msg);

end

function coded = caesar(arr, num)

size = strlength(arr);

coded = arr+num

for i = 1:size

while coded(i)> 126

coded(i) = coded(i) - 95;

end

while coded(i) < 32

coded(i) = coded(i) + 95;

end

end

coded = char(coded);

end

This problem is asking you to shift the character variable by a given element n

the word wrap means that if the ASCII code of your character exceeds 32 or 126 you need to circle back again .

For example

if ASCII code is 97 and n (shift variable) is 45 so your ASCII code is 142 which exceeds 126. So you need to subtract 126 from 142

142-126, and add the net result to 31.

you need'nt do all that..... use the function called circshift

so i defined a character array from 32 to 126 which is the required ascii range

these are the characters.

ch =

' !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~'

and when i use the circshift command

ch_shift_pos=circshift(ch,2)

ch_shift_pos =

'}~ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|'

ch_shift_neg=circshift(ch,-2)

ch_shift_neg=

'"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ !'

Notice how the characters have shifted by 2 positions without you having to manually keep it within its range.

now if i want to find a character and its corresponding encrypted/shifted value i simply transfer the index since both ch and ch_shift are of the samesize

so for example: if i want to find the encryption character of a , i first find the index of a in the 'ch' array and store it in a variable called x

and then i use that index to find the encryption in the shifted array

ch_shift_pos(x)

ans =

'_'

ch_shift_neg(x)

ans =

'c'

There! thats your answer. As simple as that. But i had to rack my brains for it. :P

function coded = caesar(str,n)

num1 = double(str);

for i = 1 : length(num1)

if num1(i) + n > 126

m = num1(i)-126+n;

p = 31+m;

num1(i) = p;

elseif num1(i)+n < 32

m = 32 - num1(i) + n;

p = 126 - m;

num1(i) = p;

else m = num1(i) + n;

num1(i) = m;

end

code(i) = num1(i);

end

coded = char(code);

I have written this code. Can anyone please expain as what is wrong in here? I know i have made a mistake. But i am not able to figure it out.

Thanks in advance.

function [coded]= caesar(code , shift)

A = double(code);

x = 1;

z = length(A);

z = z+ 1;

shift = shift - 95*(fix(shift/95));

code(1:end) = code(1:end) + shift;

while x ~= z

if code(1,x)< 32

A(1,x) = A(1,x) - 32;

A(1,x) = A(1,x) + shift;

A(1,x) = A(1,x) + 127;

elseif (code(1,x)>32)&&(code(1,x)<127)

A(1,x) = A(1,x) + shift;

else

A(1,x) = A(1,x) - 127;

A(1,x) = A(1,x) + shift;

A(1,x) = A(1,x) + 32;

end

x= x + 1;

end

coded = char(A);

end

function txt = caesar(txt,key)

txt = double(txt) + key;

first = double(' ');

last = double('~');

txt = char(mod(txt - first,last - first + 1) + first);

end

function y = caesar2(ch, key)

v = ' ' : '~';

[~, loc] = ismember(ch, v);

v2 = circshift(v, -key);

y = v2(loc);

end

function coded = caesar(ctbe,sa)

dd = double(ctbe)

if dd>=32 & dd<=126

ss =dd +sa

ss(ss<32) = rem((ss(ss<32)-32),95)+127

ss(ss>126)=rem((ss(ss>126)-126),95)+31

coded =char(ss);

end

end

Short code with use of Logical Indexing:

function coded= caesar(string,shift)

mod_str=string+shift;

for i=1:length(mod_str)

mod_str(mod_str<32)=mod_str(mod_str<32)+95;

mod_str(mod_str>126)=mod_str(mod_str>126)-95;

end

coded=char(mod_str);

function coded = caesar(V,N)

ascii = char(32:126);

coded1 = (double(V) + N - 31);

found = false;

ii = 1;

coded2 = [];

while ~(found)

if ii < length(coded1)+1

j = coded1(ii);

ii = ii +1;

while j < 32

j = j + 126 - 31;

end

while j > length(ascii)

j = j - length(ascii);

end

coded2 = abs([coded2,j]);

else

found = true;

break;

end

end

coded = ascii(coded2);

help me in this . i wrote this code but i am getting error please tell me what's wrong in this

function y=caesar(a,b)

q=double(a);

for i=1:length(a)

d(i)=q(i)+b;

if d(i)>=32;

e(i)=rem(d(i),126);

else

e(i)=95+d(i);

end

if e(i)>=32 ;

y(i)=char(e(i));

elseif e(i)==0;

y(i)=char(126);

else

e(i)=e(i)+31;

y(i)=char(e(i));

end

end

end

function coded=caesar(c,s)

n=mod(s,95);

sc=c+n;

l=length(sc);

w=[];

for i=1:l

if sc(i)>126

p=31+(sc(i)-126);

elseif sc(i)<32

p=126-abs(sc(i)-31);

else

p=sc(i);

end

w=[w p];

end

coded=char(w);

end

The code below is a long one but it is using a while loop and if you read it, it is an easy one and it is correct for any random shifts.

function coded = caesar(A,n)

a = double(A);

z = a + n;

for i =1: length(a)

if z(i)>126

b = z(i) - 126;

if b <=95

z(i) = 31 + b;

else

while b > 95

b = b-95;

end

z(i) = 31 + b;

end

end

if z(i) < 32

c = 32 - z(i);

if c <= 95

z(i) = 127 - c;

else

while c >95

c = c - 95;

end

z(i) = 127 -c;

end

end

end

encrypted_code = z;

coded = char(encrypted_code);

end

This code is quite lenghty, but logic that i have used is quite simple understand

function coded = caesar(A, n)

a = double(A)

ele=size(a)

for i=1:ele(1,2)

if n>=0

for j=1:n

a(i) = a(i)+1;

if a(i)>126

a(i)=32;

end

end

end

if n<0

for j=1:abs(n)

a(i) = a(i)-1;

if a(i)<32

a(i)=126;

end

end

end

end

coded = char(a);

end

function coded = caesar(M, n)

num = double(M);

num2 = num;

N = n - 95 * fix(n/95);

for i = 1:length(num);

if num(i) + N < 32

num2(i) = 126 - (31- num(i) - N);

elseif num(i) + N > 126

num2(i) = 32 + (num(i) + N -127);

else

num2(i) = num(i) + N ;

end

coded = char(num2);

end

(using mod function)

function txt = caesar(txt,key)

txt = double(txt) + key;

first = double(' ');

last = double('~');

txt = char(mod(txt - first,last - first + 1) + first);

end

(using circ shify function)

function y = caesar2(ch, key)

v = ' ' : '~';

[~, loc] = ismember(ch, v);

v2 = circshift(v, -key);

y = v2(loc);

end

function coded = caesar(message,code)

while(code>95)

code=code-95;

end

while(code<-95)

code=code+95;

end

message=message+code;

message(message>126)=char(double(message(message>126))-95)

message(message<32)=char(double(message(message<32))+95)

coded=char(message);

end

function coded=caesar(v,n)

x=double(v)+n;

q=x(x<32);

p=x(x>126);

while q<32;

x(x<32)=x(x<32)+95;

q=x(x<32);

end

while p>126;

x(x>126)=x(x>126)-95;

p=x(x>126);

end

coded=char(x);

end

here you go

function [coded]=caesar(a,shift)

m=double(a)

codedd=m+shift;

for i=1:abs(shift)

codedd(codedd<32)=127-(32-codedd(codedd<32));

codedd(codedd>126)=31+(codedd(codedd>126)-126)

coded=char(codedd)

end

end

function coded = caesar(char_vec,shift_amount)

char_value = char_vec+shift_amount;

for ii = 1:length(char_value)

if char_value>126

coded = char(char_value-95);

elseif char_value<32

coded = char(char_value+95);

else

coded = char(char_value);

end

end

end

I got correct output but in the assignment when i run this program it shows error...What fault i did i m unable to notice,if anyone can explain me then plz help me.

I'm beginner and I have written this code. Can anybody help me by expaining that what is wrong in here?

function coded = caesar(string,shift)

double_A = double(string);

position = double_A + shift;

for ii = 1:length(position)

if position > 126

new_position = position - 95;

elseif position < 32

new_position = position + 95;

else

new_position = position;

end

end

coded = char(new_position);

end

function coded=caesar(a,b)

x=double(a);

k=mod(b,95);

q=[];

for j=1:length(x)

p=x(j)+k;

if p<=126 && p>=32

q=[q p];

elseif p>126

r=p-95;

q=[q r] ;

elseif p<32

s=p+95;

q=[q s];

end

end

coded=char(q);

end

A much shorter solution is possible using logical arrays.

function coded =caesar(str, n)

coded = str + n;

while ( sum(coded >= 127) > 0 || sum(coded <= 31) >0 )

coded(coded >= 127) = 31 + (coded(coded>=127)-126);

coded(coded <= 31) = 127 - (32-coded(coded<=31));

end

coded = char(coded);

The while loop condition simply ensures that there is no overflow after each round of correction

The important thing is your output should be a string

function coded= caesar(v,s)

v=v+s;

v(v>126)=rem(v(v>126),95);

v(v<32)=127-rem(32-v(v<32),95);

coded=char(v);

function cloud=caesar(m,n)

sum=double(m+n);

for i=1:length(sum)

if n>0

if (sum(i)<127)

cloud(i)=char(sum(i));

elseif sum(i)>126

store=sum(i)-126;

sto=mod(store,95);

if sto==0

s=126;

cloud(i)=char(s+sto);

else

s=32;

cloud(i)=char(s+sto-1);

end

end

else

if n<0

if (sum(i)>=32)

cloud(i)=char(sum(i));

else

if sum(i)<32

store=32-sum(i);

sto=mod(store,95);

cloud(i)=char(126-sto+1);

end

end

end

end

end

end

function [coded] = caesar(v ,sa)

secret = double(v);

code = ones(1, length(v));

for ii=1:length(secret)

if secret(ii)+sa > 126

remainder=rem(sa,95);

if remainder + secret(ii)>126

code(ii)=31+(remainder-(126-secret(ii)));

else

code(ii)=remainder+secret(ii);

end

elseif secret(ii)+sa < 32

remainder=abs(rem(sa,95));

if secret(ii)-remainder < 32

code(ii)=127-(remainder-(secret(ii)-32));

else

code(ii)=secret(ii)-remainder;

end

else

code(ii) = sa + secret(ii);

end

end

coded=char(code);

end

simple and fast

function coded = caesar(txt,nr)

char_set=char(32):char(126);

char_set3=[char_set char_set char_set];

coded = char_set3(txt+64+nr-floor(nr/95)*95);

end

function txt = caesar(txt,key)

txt = double(txt) + key;

first = double(' ');

last = double('~');

txt = char(mod(txt - first,last - first + 1) + first);

end

This also helps to solve the problem. Try it

Can someone help to explain how the ismember function work in this provided solution? Why it returns double instead of strings? Thanks in advance.

function coded=caesar(c,n)

while x(a)<32 || x(a)>126

I am agree with @Wilver Sánchez's solution. I highly recommend avoiding to use "for loop" (it is not the wrong way, but it sometimes increases the processing time; maybe not for this code).

for ii = 1:length(unicodeMessage)

secret(secret < 32) = ...

Then, my solution is that:

function coded = caesar(M,s)

codes = highest - lowest + 1;

unicodeMessage = double(M);

secret = unicodeMessage + res;

secret(secret < 32) = 126 - (31 - secret(secret < 32));

secret(secret > 126) = 32 + (secret(secret > 126) - 127);

function out = caesar(m,n) m = double(m)+n; m = mod(m,95); m(m>126) = m(m>126)-126 +31; m(m<32) = m(m<32) -32+127; out = char(m);

%Help required

function coded = caesar(X,Y)

coded=fprintf('%s',code);

coded=fprintf('%s',code);

coded=fprintf('%s',code);

Hi folks,

I write this code, this is working fine with the problem.

Need further improvement if any from seniors as I'm very novice in coding and MATLAB. It took almost 90 minutes to solve.

function coded = caesar(a,b)

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