Question

How can we know when the code implementation of a cryptographic algorithm is correct to use? Justify your answer.

Answer 1

Cryptiographic: when the program converts the plan text to cipher text and cipher text to the plan text.

Then we can say that that code is correctly implemented the cryptographic. The following example will explain the cryptographic encryption and decryption.

Encryption: converts the plain text to cipher text

Decryption: Coneverts the cipher text to plain text

C++ Source Code:

#include<iostream>

using namespace std;

int main()
{
char data[100], ch;
int i, cryptokey;
char choice[1];
do
{
cout<<"\nEnter your choice \n E->Encryption\nD->Decryption\nQ->Quit\n";
cin>>choice;
if(choice[0]=='e' || choice[0]=='E')
{
cout << "Enter a message to encrypt: ";
cin>>data;
cout << "Enter key: ";
cin >> cryptokey;
  
for(i = 0; data[i] != '\0'; ++i){
ch = data[i];
  
if(ch >= 'a' && ch <= 'z'){
ch = ch + cryptokey;
  
if(ch > 'z'){
ch = ch - 'z' + 'a' - 1;
}
  
data[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch + cryptokey;
  
if(ch > 'Z'){
ch = ch - 'Z' + 'A' - 1;
}
  
data[i] = ch;
}
}
  
cout << "Encrypted message: " << data;
}
else if(choice[0]=='d' || choice[0]=='D')
{
cout << "Enter a message to decrypt: ";
cin>>data;
cout << "Enter key: ";
cin >> cryptokey;
  
for(i = 0; data[i] != '\0'; ++i){
ch = data[i];
  
if(ch >= 'a' && ch <= 'z'){
ch = ch - cryptokey;
  
if(ch < 'a'){
ch = ch + 'z' - 'a' + 1;
}
  
data[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch - cryptokey;
  
if(ch > 'a'){
ch = ch + 'Z' - 'A' + 1;
}
  
data[i] = ch;
}
}
  
cout << "Decrypted message: " << data;
}
}while(choice[0]!='Q');
  
  
return 0;
}

Output:

Enter your choice

E->Encryption

D->Decryption

Q->Quit

E

Enter a message to encrypt: hemanth

Enter key: 5

Encrypted message: mjrfsym

Enter your choice

E->Encryption

D->Decryption

Q->Quit

D

Enter a message to decrypt: mjrfsym

Enter key: 5

Decrypted message: hemanth

Enter your choice

E->Encryption

D->Decryption

Q->Quit

Q