Question

DO IN C++

Secret Codes!

Create a program that will accept a message from the user and either
encrypt ordecrypt it with the following algorithms:

To encrypt:

- get the character you wish to encrypt

- find the index of that character in the alphabet array

- add the shift offset to the index

- add the increment to the index

- "wrap around" the new index so the result is between 0 and 29

- find the character at the new index

To decrypt:

- get the character you wish to decrypt

- find the index of that character in the alphabet array

- subtract the shift offset from the index

- subtract the increment from the index

- "wrap around" the new index so the result is between 0 and 29

- find the character at the new index

- repeat steps 1-6 for every shift offset

The alphabet is <space>,a-z(lowercase),<period>,<question mark>,
and <comma> in that order.

The increment should be +3 per letter position.

Here is a sample message. Who said it?

f..yqjrnvrpuabefw.j,ddxgcndpxmsdehsomjkcydfygtd.rrp?dgstmvxmf.wo?jxgrneslzifrgzyqv.v

Answer 1

#include <iostream>
using namespace std;

char c[]= {' ', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm','n','o','p','q','r','s','t','u','v','w','x','y','z', '.', '?', ','};
int inc = 3;

string encrypt(string text, int s)
{
string result = "";

// traverse text
for (int i=0;i<text.length();i++)
{
if (islower(text[i]))
result += c[((text[i] - 'a' + 1) + s + inc)%30];
else if (text[i] == ' ')
{
result += c[(0 + s + inc)%30];
}
else if (text[i] == '.')
{
result += c[(27 + s + inc)%30];
}
else if (text[i] == '?')
{
result += c[(28 + s + inc)%30];
}
else if (text[i] == ',')
{
result += c[(29 + s + inc)%30];
}
else
{
result += text[i];
}
}

// Return the resulting string
return result;
}

int wrapIndex(int i, int i_max) {
return ((i % i_max) + i_max) % i_max;
}

string decryptHelper(string text, int s)
{
string result = "";

// traverse text
for (int i=0;i<text.length();i++)
{
if (islower(text[i]))
result += c[wrapIndex((text[i] - 'a' + 1) - s - inc, 30)];
else if (text[i] == ' ')
{
result += c[wrapIndex(0 - s - inc, 30)];
}
else if (text[i] == '.')
{
result += c[wrapIndex(27 - s - inc, 30)];
}
else if (text[i] == '?')
{
result += c[wrapIndex(28 - s - inc, 30)];
}
else if (text[i] == ',')
{
result += c[wrapIndex(29 - s - inc, 30)];
}
else
{
result += text[i];
}
}

// Return the resulting string
return result;
}

void decrypt(string text)
{
for (int i = 0; i < 30; i++)
{
cout << "Shift s: " << i << " decrypted string: " << decryptHelper(text, i) << endl;
}
}

// Driver program to test the above function
int main()
{
string text;
cout << "Enter a message to encryot or decrypt: ";
cin >> text;

string choice;
cout << "Enter 1. for encrypting this message and any other key for decryting: ";
cin >> choice;

if (choice == "1")
{
    int s;
    cout << "Enter shift : ";
    cin >> s;

    cout << "Text : " << text;
    cout << "\nShift: " << s;
    string cipher = encrypt(text, s);
    cout << "\nCipher: " << cipher << endl;

}
else
{
    cout << "Possible decryption: " << endl;
    decrypt(text);
}

return 0;
}

/*
Text : attackatonce
Shift: 4
Cipher: h..hjrh.vujlPossible decryption:
Shift s: 0 decrypted string: exxegoexsrgi
Shift s: 1 decrypted string: dwwdfndwrqfh
Shift s: 2 decrypted string: cvvcemcvqpeg
Shift s: 3 decrypted string: buubdlbupodf
Shift s: 4 decrypted string: attackatonce
Shift s: 5 decrypted string: ss bj snmbd
Shift s: 6 decrypted string: ,rr,ai,rmlac
Shift s: 7 decrypted string: ?qq? h?qlk b
Shift s: 8 decrypted string: .pp.,g.pkj,a
Shift s: 9 decrypted string: zooz?fzoji?
Shift s: 10 decrypted string: ynny.eynih.,
Shift s: 11 decrypted string: xmmxzdxmhgz?
Shift s: 12 decrypted string: wllwycwlgfy.
Shift s: 13 decrypted string: vkkvxbvkfexz
Shift s: 14 decrypted string: ujjuwaujedwy
Shift s: 15 decrypted string: tiitv tidcvx
Shift s: 16 decrypted string: shhsu,shcbuw
Shift s: 17 decrypted string: rggrt?rgbatv
Shift s: 18 decrypted string: qffqs.qfa su
Shift s: 19 decrypted string: peeprzpe ,rt
Shift s: 20 decrypted string: oddoqyod,?qs
Shift s: 21 decrypted string: nccnpxnc?.pr
Shift s: 22 decrypted string: mbbmowmb.zoq
Shift s: 23 decrypted string: laalnvlazynp
Shift s: 24 decrypted string: k kmuk yxmo
Shift s: 25 decrypted string: j,,jltj,xwln
Shift s: 26 decrypted string: i??iksi?wvkm
Shift s: 27 decrypted string: h..hjrh.vujl
Shift s: 28 decrypted string: gzzgiqgzutik
Shift s: 29 decrypted string: fyyfhpfytshj
Given cipher: f..yqjrnvrpuabefw.j,ddxgcndpxmsdehsomjkcydfygtd.rrp?dgstmvxmf.wo?jxgrneslzifrgzyqv.v
Possible decryption:
Shift s: 0 decrypted string: cxxvngoksomr?,bctxgzaaud kamujpabepljgh vacvdqaxoomyadpqjsujcxtlygudokbpiwfcodwvnsxs
Shift s: 1 decrypted string: bwwumfnjrnlq.?abswfy tc,j ltio adokifg,u bucp wnnlx copirtibwskxftcnjaohvebncvumrwr
Shift s: 2 decrypted string: avvtlemiqmkpz. arvex,,sb?i,kshn, cnjhef?t,atbo,vmmkw,bnohqshavrjwesbmi ngudambutlqvq
Shift s: 3 decrypted string: uuskdlhpljoyz, qudw??ra.h?jrgm?,bmigde.s? san?ulljv?amngprg uqivdralh,mftc latskpup
Shift s: 4 decrypted string: ,ttrjckgokinxy?,ptcv..q zg.iqfl.?alhfcdzr.,r m.tkkiu. lmfoqf,tphucq kg?lesb,k srjoto
Shift s: 5 decrypted string: ?ssqibjfnjhmwx.?osbuzzp,yfzhpekz. kgebcyqz?q,lzsjjhtz,klenpe?sogtbp,jf.kdra?j,rqinsn
Shift s: 6 decrypted string: .rrphaiemiglvwz.nratyyo?xeygodjyz,jfdabxpy.p?kyriigsy?jkdmod.rnfsao?iezjcq .i?qphmrm
Shift s: 7 decrypted string: zqqog hdlhfkuvyzmq sxxn.wdxfncixy?iec awoxzo.jxqhhfrx.ijclnczqmer n.hdyibp,zh.poglql
Shift s: 8 decrypted string: yppnf,gckgejtuxylp,rwwmzvcwembhwx.hdb, vnwynziwpggeqwzhibkmbypldq,mzgcxhao?ygzonfkpk
Shift s: 9 decrypted string: xoome?fbjfdistwxko?qvvlyubvdlagvwzgca?,umvxmyhvoffdpvyghajlaxokcp?lyfbwg n.xfynmejoj
Shift s: 10 decrypted string: wnnld.eaiechrsvwjn.puukxtauck fuvyfb .?tluwlxguneecouxfg ik wnjbo.kxeavf,mzwexmldini
Shift s: 11 decrypted string: vmmkczd hdbgqruvimzottjws tbj,etuxea,z.sktvkwftmddbntwef,hj,vmianzjwd ue?lyvdwlkchmh
Shift s: 12 decrypted string: ulljbyc,gcafpqtuhlynssivr,sai?dstwd ?yzrjsujveslccamsvde?gi?ulh myivc,td.kxucvkjbglg
Shift s: 13 decrypted string: tkkiaxb?fb eopstgkxmrrhuq?r h.crsvc,.xyqirtiudrkbb lrucd.fh.tkg,lxhub?sczjwtbujiafkf
Shift s: 14 decrypted string: sjjh wa.ea,dnorsfjwlqqgtp.q,gzbqrub?zwxphqshtcqjaa,kqtbczegzsjf?kwgta.rbyivsatih eje
Shift s: 15 decrypted string: riig,v zd ?cmnqreivkppfsozp?fyapqta.yvwogprgsbpi ?jpsabydfyrie.jvfs zqaxhur shg,did
Shift s: 16 decrypted string: qhhf?u,yc,.blmpqdhujooernyo.ex ops zxuvnfoqfraoh,,.ior axcexqhdziuer,yp wgtq,rgf?chc
Shift s: 17 decrypted string: pgge.t?xb?zaklopcgtinndqmxnzdw,nor,ywtumenpeq ng??zhnq, wbdwpgcyhtdq?xo,vfsp?qfe.bgb
Shift s: 18 decrypted string: offdzs.wa.y jknobfshmmcplwmycv?mnq?xvstldmodp,mf..ygmp?,vacvofbxgscp.wn?uero.pedzafa
Shift s: 19 decrypted string: neecyrzv zx,ijmnaergllbokvlxbu.lmp.wurskclnco?lezzxflo.?u buneawfrbozvm.tdqnzodcy e
Shift s: 20 decrypted string: mddbxqyu,yw?hilm dqfkkanjukwatzklozvtqrjbkmbn.kdyyweknz.t,atmd veqanyulzscpmyncbx,d,
Shift s: 21 decrypted string: lccawpxt?xv.ghkl,cpejj mitjv syjknyuspqiajlamzjcxxvdjmyzs? slc,udp mxtkyrbolxmbaw?c?
Shift s: 22 decrypted string: kbb vows.wuzfgjk?bodii,lhsiu,rxijmxtroph ik lyibwwucilxyr.,rkb?tco,lwsjxqankwla v.b.
Shift s: 23 decrypted string: jaa,unvrzvtyefij.anchh?kgrht?qwhilwsqnog,hj,kxhavvtbhkwxqz?qja.sbn?kvriwp mjvk ,uzaz
Shift s: 24 decrypted string: i ?tmuqyusxdehiz mbgg.jfqgs.pvghkvrpmnf?gi?jwg uusagjvwpy.pi zram.juqhvo,liuj,?ty y
Shift s: 25 decrypted string: h,,.sltpxtrwcdghy,laffziepfrzoufgjuqolme.fh.ivf,ttr fiuvoxzoh,yq lzitpgun?khti?.sx,x
Shift s: 26 decrypted string: g??zrksowsqvbcfgx?k eeyhdoeqyntefitpnkldzegzhue?ssq,ehtunwyng?xp,kyhsoftm.jgsh.zrw?w
Shift s: 27 decrypted string: f..yqjrnvrpuabefw.j,ddxgcndpxmsdehsomjkcydfygtd.rrp?dgstmvxmf.wo?jxgrneslzifrgzyqv.v
Shift s: 28 decrypted string: ezzxpiqmuqot adevzi?ccwfbmcowlrcdgrnlijbxcexfsczqqo.cfrsluwlezvn.iwfqmdrkyheqfyxpuzu
Shift s: 29 decrypted string: dyywohpltpns, cduyh.bbvealbnvkqbcfqmkhiawbdwerbyppnzbeqrktvkdyumzhveplcqjxgdpexwotyt

*/