Question

Question: Please Provide Comments on each Line of code explaining what the C Function is doing throughout the code.

// Function used for substitution encryption  
                 
void SubEncrypt(char *message, char *encryptKey) {
int iteration = 0;
printf("Enter Aphabet Encryption Key: \n");
scanf("%s", encryptKey);

  
for (iteration = 0; iteration < strlen(message); iteration++)
{
char letter = message[iteration];
if (letter >= 'A' && letter <= 'Z')
{
  
letter = encryptKey[letter - 'A'];
}

message[iteration] = letter;
}
printf("CipherText message: %s\n", message);
}

//_________________________________________________________________________________________________________________________________________________
// Function used for substitution decryption

void SubDecrypt(char *message, char *encryptKey) {
int iteration;
int iteration_Num_Two = 0;
int letter;
printf("Enter Encryption Key: \n");
scanf("%s", encryptKey);
for (iteration = 0; message[iteration] != '0'; iteration++)
{
letter = message[iteration];
if (letter >= 'A' && letter <= 'Z')
{
letter = letter - 32;
}
if (letter >= 65 && letter <= 90) {
  
for (iteration_Num_Two = 0; iteration_Num_Two < 27; iteration_Num_Two++)
{
if (message[iteration] == encryptKey[iteration_Num_Two])
{
break;
}
}
message[iteration] = 'A' + iteration_Num_Two;
  
}
printf("%s\n", message);

}
;
printf("CipherText message: %s\n", message);
printf("%s\n", encryptKey);
}

// End Function Void SubDecrypt
//_________________________________________________________________________________________________________________________________________________

// Function used for rotation decryption without using a key

void RotDecrypt_Without_Key(char *message, int key) {
printf("Enter ciphertext to decrypt: \n");
  
int iteration;
char letter;
int count = 1;
  
for (count = 1; count <26; count++) {
  
for(iteration = 0; message[iteration] != '\0'; ++iteration){
letter = message[iteration];
key = 1;
  
if(letter >= 'A' && letter <= 'Z'){
letter = letter - key;
  
if(letter < 'A'){
letter = letter + 'Z' - 'A' + 1;
}
  
message[iteration] = letter;
}
  
  
else if(letter >= 'a' && letter <= 'z'){
letter = letter - key;
  
if(letter < 'a'){
letter = letter + 'z' - 'a' + 1;
}
  
message[iteration] = letter;
}
  
key = key++;
}
  
printf("Plaintext message: %s\n", message);
  
}
  
}

// End Function Void RotDecrypt_Without_Key

Answer 1

// Function used for substitution encryption

void SubEncrypt(char *message, char *encryptKey)
{
int iteration = 0;
//display the message to input Alphabet Encryption key
printf("Enter Aphabet Encryption Key: \n");
//read the encryption key
scanf("%s", encryptKey);

//loop will continue from 0 to the end of message
for (iteration = 0; iteration < strlen(message); iteration++)
{
   //assign the character at message[iteration] to letter
char letter = message[iteration];
//check for uppercase character
if (letter >= 'A' && letter <= 'Z')
{
//update the value of letter by assigning the chracter at encryptKey[letter-'A']
letter = encryptKey[letter - 'A'];
}
//store the letter to message[iteration]
message[iteration] = letter;
}
//display the cipher text
printf("CipherText message: %s\n", message);
}

//_________________________________________________________________________________________________________________________________________________
// Function used for substitution decryption

void SubDecrypt(char *message, char *encryptKey)
{
int iteration;
int iteration_Num_Two = 0;
int letter;
//display the message to enter encryption key
printf("Enter Encryption Key: \n");
//Input the Encryption key
scanf("%s", encryptKey);
//loop will continue till message reaches to end
for (iteration = 0; message[iteration] != '0'; iteration++)
{
   //assign the first character of message to letter
letter = message[iteration];
//check the letter is between 'A' to 'Z' i.e/ upper case character or not
if (letter >= 'A' && letter <= 'Z')
{ //move the letter to 32 characters back
letter = letter - 32;
}
//after subtraction if the letter lies in the range 65 to 90(inclusive)
if (letter >= 65 && letter <= 90)
{
//loop will continue from 0 to 26
for (iteration_Num_Two = 0; iteration_Num_Two < 27; iteration_Num_Two++)
{
   //check if the message[iteration] and encryptKey[iteration_Num_Two] will equal then terminate the loop
if (message[iteration] == encryptKey[iteration_Num_Two])
{
break;
}
}
//set the message[iteration] to the value of iteration_Num_Two+'A'(uppercase) i.e/ 65+iteration_Num_Two
message[iteration] = 'A' + iteration_Num_Two;
  
}
//display the message
printf("%s\n", message);

}
//display the cipher text
printf("CipherText message: %s\n", message);
//display the encryptKey
printf("%s\n", encryptKey);
}

// End Function Void SubDecrypt
//_________________________________________________________________________________________________________________________________________________

// Function used for rotation decryption without using a key

void RotDecrypt_Without_Key(char *message, int key) {
//display a message
printf("Enter ciphertext to decrypt: \n");
  
int iteration;
char letter;
int count = 1;
//loop runs from 1 to 25
for (count = 1; count <26; count++)
{
//loop will continue till message reaches to end
for(iteration = 0; message[iteration] != '\0'; ++iteration)
{
   //assign each character of message to letter
letter = message[iteration];
key = 1; //assign key to 1
//check whetehr the letter is between A to Z (UPPERCASE CHARACTER)
if(letter >= 'A' && letter <= 'Z')
{
   //shift the letter one step back
letter = letter - key;
//after subtracting the key from letter if it goes beyond A
//then it will assgn the letter to Z (cyclic process)
if(letter < 'A'){
letter = letter + 'Z' - 'A' + 1;
}
//REASSIGN THE changed letter to message[iteration]
message[iteration] = letter;
}
  
//check whetehr the letter is between A to Z (UPPERCASE CHARACTER)
else if(letter >= 'a' && letter <= 'z'){
letter = letter - key;   //shift the letter one step back
//after subtracting the key from letter if it goes beyond a
//then it will assgn the letter to z (cyclic process)
if(letter < 'a'){
letter = letter + 'z' - 'a' + 1;
}
//REASSIGN THE changed letter to message[iteration]
message[iteration] = letter;
}
//increse the valeu of key by 1
key = key++;
}
//display the plain text
printf("Plaintext message: %s\n", message);
  
}
  
}

// End Function Void RotDecrypt_Without_Key