An Algorithm to implement Simplified-DES encryption

Simplified-DES.cpp

/arcade-town-games-key-generator.html. Step6: As we know S-DES has two round and for that we also need two keys, one key we generate in the above steps (step 1 to step 5). Now we need to generate a second bit and after that we will move to encrypt the plain text or message. It is simple to generate the second key. Question: Look Up S-DES (you Can Use Your Main Book Or An Online Source), And Solve The Following: Based On S-DES Key Generation, If The Input Of P8 In Round 2 Is, Find The Shared 10-bit Key K. P10: 3 5 2 74 10 9 8 6 P8: 6 348 510 9 And The Diagram For Key Generation Is The Following: 6 10-bit Key 10 P 10 LS-1 LS-1 P 8 K2 LS-2 LS-2 P 8.

// Algorithm to implement simplified - DES encryption

#include<bits/stdc++.h>

usingnamespacestd;

string Permutation(vector<int> array, string inp){

string out = '';

for(int i=0;i<array.size();i++)

out += inp[array[i]-1];

return out;

}

classS_DES{

public:

string KEY,K1,K2,IPOut,InvIPOut;

string F1Out;

string INPUT,OUTPUT;

voidinitialize(string key){

if(key.size()!=10){

cout<<'nInValid Key-Length '<<key<<''<<key.size();

exit(1);

}

KEY = key;

Keys_Generation();

}

voidKeys_Generation(){

cout<<'Enter P10 permutation array: ';

vector<int> P10(10,0);

for(int i=0;i<10;i++)

cin>>P10[i];

string P10_output = Permutation(P10,KEY);

cout<<'P10 output while generating key: '<<P10_output<<endl;

string P10_left = P10_output.substr(0,5), P10_right = P10_output.substr(5,5);

string pl = LShift(P10_left,1), pr = LShift(P10_right,1);

string plpr = pl+pr;

cout<<'Enter P8 permutation array: ';

vector<int> P8(10,0);

for(int i=0;i<8;i++)

cin>>P8[i];

K1 = Permutation(P8,plpr);

cout<<'K1: '<<K1<<endl;

string pl1=LShift(pl,2), pr1=LShift(pr,2);

plpr = pl1+pr1;

K2 = Permutation(P8,plpr);

cout<<'K2: '<<K2<<endl;

}

string LShift(string input,int n){

string output = input;

char firstbit;

while(n--){

firstbit = output[0];

output = output.substr(1,output.size()-1);

output += firstbit;

}

return output;

}

voidDES_Encryption(){

IP();

string LIP = IPOut.substr(0,4);

string RIP = IPOut.substr(4,4);

cout<<'IP output: '<<IPOut<<endl;

Function_F(LIP,RIP,1);

cout<<'Fn Output: '<<F1Out<<endl;

string L1 = F1Out.substr(0,4), R1 = F1Out.substr(4,4);

Function_F(R1,L1,2);

cout<<'Fn Output second time: '<<F1Out<<endl;

InvIP(F1Out);

cout<<'Encrypted Cipher-string: '<<InvIPOut<<endl;

}

/*Method to perform Initial-Permutation*/

voidIP(){

vector<int> IP_array(8,0);

cout<<'Enter initial Permutation array: ';

for(int i=0;i<8;i++)

cin>>IP_array[i];

IPOut = Permutation(IP_array,INPUT);

}

/*Method to perform Inverse of Initial-Permutation*/

voidInvIP(string input){

vector<int> InvIPArray(8,0);

cout<<'Enter Inverse initial Permutation: ';

for(int i=0;i<8;i++)

cin>>InvIPArray[i];

InvIPOut = Permutation(InvIPArray,input);

}

voidFunction_F(string linput,string rinput,int key)

{

cout<<'Enter E/P array: ';

vector<int> E_P(8,0);

for(int i=0;i<8;i++)

cin>>E_P[i];

string E_POutput = Permutation(E_P,rinput);

string EXOR_Output;

if(key 1)

EXOR_Output = EX_OR(E_POutput,K1);

else

EXOR_Output = EX_OR(E_POutput,K2);

string LEXOR = EXOR_Output.substr(0,4),REXOR = EXOR_Output.substr(4,4);

string SBOX0_Output=SBOX0(LEXOR);

string SBOX1_Output=SBOX1(REXOR);

string SBOX_Output = SBOX0_Output+SBOX1_Output;

cout<<'Enter P4 Operation array: ';

vector<int> P4(4,0);

for(int i=0;i<4;i++)

cin>>P4[i];

string P4_Output = Permutation(P4,SBOX_Output);

string fk_Output = EX_OR(P4_Output,linput);

F1Out = fk_Output + rinput;

}

string EX_OR(string a,string b){

string output = '';

for(int i=0;i<a.size();i++){

if(a[i] b[i])

output += '0';

else

output += '1';

}

return output;

}

string SBOX0(string l)

{

cout<<'Enter Input for S0n';

vector<int> temp(4,0);

vector<vector<int> > S0(4,temp);

for(int i=0;i<4;i++){

for(int j = 0;j<4;j++)

cin>>S0[i][j];

}

string bits[]={'00','01','10','11'};

string lrow = l.substr(0,1)+l.substr(3,1),lcol = l.substr(1,1)+l.substr(2,1);

string SO;

int i,lr,lc,b;

for(i=0;i<4;i++){

if(lrow bits[i])

lr=i;

if(lcol bits[i])

lc=i;

}

b=S0[lr][lc];

return bits[b];

}

string SBOX1(string l)

{

cout<<'Enter Input for S1n';

vector<int> temp(4,0);

vector<vector<int> > S0(4,temp);

for(int i=0;i<4;i++){

for(int j = 0;j<4;j++)

cin>>S0[i][j];

}

string bits[]={'00','01','10','11'};

string lrow = l.substr(0,1)+l.substr(3,1),lcol = l.substr(1,1)+l.substr(2,1);

string SO;

int i,lr,lc,b;

for(i=0;i<4;i++){

if(lrow bits[i])

lr=i;

if(lcol bits[i])

lc=i;

}

b=S0[lr][lc];

return bits[b];

}

};

intmain()

{

int i,n=10,choice;

string key;

S_DES S;

while(1){

cout<<'nWhat do you want to do.n1. Encryptionn2. ExitnnEnter the choice? ';

cin>>choice;

switch(choice){

case1:

cout<<'nEnter the 10-bits KEY: ';

cin>>key;

cout<<'nNotedown this key, as same key is used for Decryptionn';

S.initialize(key);

cout<<'Enter string to encrypt: ';

cin>>S.INPUT;

S.DES_Encryption();

break;

case2:

exit(0);

default:

cout<<'nWrong Choice Enter againnPress any key to return to Main Menu.';

break;

}

return0;

}

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