In this article I will be explaining the very basics of encryption and decryption techniques. I will be discussing two types of encryption/ decryption techniques 1. Caesar Cipher 2. Vigenere Cipher (basic and advanced)
In this article I will be explaining the very basics of encryption and decryption techniques.
Here I will be discussing two types of encryption/ decryption techniques
1. Caesar Cipher
2. Vigenere Cipher (basic and advance)
I will be explaining in detail how the, encryption of basic types, are to be done and I have not used any complex crypto methods for the coding part.
Let's begin
Here I will be discussing two types of encryption/ decryption techniques
1. Caesar Cipher
2. Vigenere Cipher (basic and advance)
I will be explaining in detail how the, encryption of basic types, are to be done and I have not used any complex crypto methods for the coding part.
Let's begin
Caesar Cipher encryption/decryption
A brief history: In cryptography, a Caesar cipher, also known as a Caesar's cipher or the shift cipher or Caesar's code or Caesar shift, is one of the simplest and basic known encryption techniques.
It is a type of replace cipher in which each letter in the plaintext is replaced by a letter with a fixed position separated by a numerical value used as a "key".
Caesar Cipher is or was probably the very first encryption methodology.
Let me give an example:
Let's take a plain text: "DOTNETSPIDER IS A LEADING WEBSITE FOR DOT NET COMMUNITY" and we want to encrypt the plain text using "Caesar Cipher", using key/password as "9". Caesar Cipher only takes numeric password, and only between 0-25.
So our plain text's cipher/encrypted text will become: "MXCWNCBYRMNA RB J UNJMRWP FNKBRCN OXA MXC WNC LXVVDWRCH".
So how did we arrive at the cipher/encrypted text?
I will explain with a simple procedure.
Let us assign each alphabet in our English literature with a numeric value in a tabular format
Such as:
Now take a word from the plain text, for example: "DOTNETSPIDER"
As I have said earlier that it is a type of replace cipher in which each letter in the plaintext is replaced by a letter with a fixed position separated by a numerical value used as a "key".
So we have to take each letter or character,
In case of "DOTNETSPIDER": the value of 'D' is 3, so add 3 by 9 (since we have used '9' as our key/password)
So, 3 + 9 = 12
Now refer to the table above, now whose value is 12, its 'M'.
So here �D� gets replaced by �M�
Let�s take another value from �DOTNETSPIDER� ? �T�: the value of �T� is 19, so add 19 by 9 (since we have used �9� as our key/password)
So, 19 + 9 = 28,
Here you can see the value is not on the list.
So whenever the value is greater than �25�, just subtract the value with �26�.
So, 19 + 9 = 28, and now the value is greater than 25, so, 28 � 26 = 2.
Now refer to the table above, now whose value is 2, its �C�.
So here �T� gets replaced by �C�
Similarly,
O (14) + 9 = 23(X)
T (19) + 9 = 28 � 26 = 2(C)
N (13) + 9 = 22(W)
E (4) + 9 = 13(N)
T (19) + 9 = 28 � 26 = 2(C)
S (18) + 9 = 27 � 26 = 1(B)
P (15) + 9 = 24(Y)
I (8) + 9 = 17(R)
D (3) + 9 = 12(M)
E (4)+ 9 = 13 (N)
R (17) + 9 = 26 � 26 = 0(A)
Hence, �DOTNETSPIDER� became, by using Caesar Cipher �MXCWNCBYRMNA�.
Now let�s go to the coding part.
The look of my app is like this:
After encoding the text.
Now the code:
Encode/Encrypt:
//Here I am only using characters A-Z(upper case)
//To increase the complexity of the ceaser cipher lower case"a-z", Numerics and Symbols also can be used
string alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
#region Encode
private void Encode_Click(object sender, EventArgs e)
{
string Text = richTextBox1.Text.ToUpper();
int key = Convert.ToInt32( comboBox1.Text);
string final = "";
int indexOfChar = 0;
char encryptedChar;
//Convert/encrypt each and every character of the text
foreach (char c in Text)
{
//Get the index of the character from alphabets variable
indexOfChar = alphabets.IndexOf(c);
if (c == ' ')//if encounters an white space
{
final = final + c;
}
else if(c == '\n')// if encounters a new line
{
final = final + c;
}
else if ((indexOfChar + key) > 25)//if the character is at the end of the string "alphabets"
{
//encrypt the character
encryptedChar = alphabets[(indexOfChar + key) - 26];
//add the encrypted character to a string every time to get an encrypted string
final = final + encryptedChar;
}
else
{
//encrypt the character
//add the encrypted character to a string every time to get an encrypted string
encryptedChar = alphabets[indexOfChar + key];
final = final + encryptedChar;
}
}
//Display encrypted text
richTextBox1.Clear();
richTextBox1.Text = final;
}
#endregion
Decode/Decrypt
#region Decode
private void Decode_Click(object sender, EventArgs e)
{
string Text = richTextBox1.Text.ToUpper();
int key = Convert.ToInt32(comboBox1.Text);
string final = "";
int indexOfChar = 0;
char decryptedChar;
//Convert/decrypt each and every character of the text
foreach (char c in Text)
{
//Get the index of the character from alphabets variable
indexOfChar = alphabets.IndexOf(c);
if (c == ' ')//if encounters a white space
{
final = final + c;
}
else if (c == '\n')// if encounters a new line
{
final = final + c;
}
else if ((indexOfChar - key) < 0)//if the character is at the start of the string "alphabets"
{
//decrypt the character
//add the decrypted character to a string every time to get a decrypted string
decryptedChar = alphabets[(indexOfChar - key) + 26];
final = final + decryptedChar;
}
else
{
//decrypt the character
//add the decrypted character to a string every time to get a decrypted string
decryptedChar = alphabets[indexOfChar - key];
final = final + decryptedChar;
}
}
//Display decrypted text
richTextBox1.Clear();
richTextBox1.Text = final;
}
#endregion
Note: Caesar Cipher is very easy to break, as, in the above example, there is only 25 ways to encrypt and decrypt the plain/cipher text, you can include lower case alphabets, symbols and numeric to increase the number of ways, but it�s not a secure way, because it�s too easy to decrypt using trial and error methods.
End of Caesar Cipher
*****************************************
Vigenere Cipher Basic
A brief history: The Vigen�re cipher is a method of encrypting text by using a series of different Caesar ciphers based on the letters of a keyword.
It is a polyalphabetic cipher based on using successively shifted alphabets, a different shifted alphabet for each of the 26 English letters. The procedure is based on the table shown in Figure below and the use of a keyword. The letters of the keyword determine the shifted alphabets used in the encoding process.
Let me explain with an example:
Let�s take a plain text: �DOTNETSPIDER IS A LEADING WEBSITE FOR DOT NET COMMUNITY� and we want to encrypt the plain text using �Vigenere Cipher�, using key/password as �PAUL�.
So our plain text�s cipher/encrypted text will become: �SONYTTMAXDYC XS U WTAXTCG QPQSCET FIC SON YTT WZBMOYXTS�.
So how did we arrive at the cipher/encrypted text?
I will explain with a simple procedure and mathematical too.
First the simple procedure.
First you have to make the table,
The password for the above example, I have used is �PAUL�.
So from the above table only keep the sections of alphabets of �PASSWORD REFERENCE� that constitutes in the word �PAUL�(in ascending order).
That is: �A�, �L�, �P�, �U�
Let�s reduce the size of the table:
Now take a word from the plain text, for example: �DOTNETSPIDER�
And the password is �PAUL�.
Now refer �D� from the �TEXT REFERENCE� section of the table, and �P� from the �PASSWORD REFERENCE� section of the table,
Like this:
See what you get: Now replace the value of �D� with �S�
Similarly take the letter �O� from the �TEXT REFERENCE� section of the table, and �A� from the �PASSWORD REFERENCE� section of the table.
(Note: the letters if the text and password should increase by 1 simultaneously, after each encryption of the letters of the plain text)
See what you get: Now replace the value of �O� with �O�
Similarly take the letter �T� from the �TEXT REFERENCE� section of the table, and �U� from the �PASSWORD REFERENCE� section of the table.
Now replace the value of �T� with �S�
Similarly take the letter �N� from the �TEXT REFERENCE� section of the table, and �L� from the �PASSWORD REFERENCE� section of the table.
Now replace the value of �N� with �Y�
Now we have reached at the last letter of the password, so now we have to start over again with the first letter of the password.
Take the letter �E� from the �TEXT REFERENCE� section of the table, and �P� from the �PASSWORD REFERENCE� section of the table.
Now replace the value of �E� with �T�
Repeating the above steps you will get �DOTNETSPIDER�, using password as �PAUL�, The Vigenere cipher as, �SONYTTMAXDYC�.
Now let�s derive the Vigenere cipher mathematically:
First of all let�s assign a value to the alphabets, like we did in Caesar cipher above.
For Encryption the formula is:
Value of cipher text letter = (value of plain text letter + value of password text letter) (mod 26)
For Decryption the formula is:
Value of plain text letter = (value of cipher text letter - value of password text letter) (mod 26)
Let�s see with an example:
Plaintext: DOTNETSPIDER
Password : PAUL
The value of �D� from plain text is 3, and the value of �P� from password is 15.
So using the encryption formula.
(3 + 15) mod 26 = 18 mod 26 = 18.
Now refer to the table above, now whose value is 18, its �S�.
Similatly for �O�, the value of �O� from plain text is 14, and the value of �A� from password is 0.
So using the encryption formula.
(14 + 0) mod 26 = 14 mod 26 = 14.
Now refer to the table above, now whose value is 14, its �O�.
By applying the above formula for encryption, �DOTNETSPIDER� and using password as �PAUL�, The Vigenere cipher becomes, �SONYTTMAXDYC�.
End of Vigenere cipher basic
********************************************
Vigenere cipher advance
Vinegere cipher advanced is pretty much same as the basic; the only difference is that we change the structure of the text/password reference table.
In advance Vigenere cipher you will need another password which is known as �alphabet key�.
For example:
Suppose my alphabet key is �SPIDER�
The text/password reference table will be as such:
As you can see the Word �SPIDER� has been set at the first of the text/password reference table, hence this increases the complexity of Vigenere cipher.
�Vinegere Cipher Advanced� depends on how you set your alphabet key in the text/password reference table. It can be in any form such as : you can reverse the alphabet key : �SPIDER� becomes �REDIPS� or you can set the alphabet key at the end of the reference table. There are many way for the advanced version and surely it increases the complexity of the cipher/encrypted text.
In Vinegere Cipher advanced, the text replacement pattern is same as the Vinegere cipher basic, that I have explained above, the only difference is the structure of the text/password reference table.
Let�s encrypt a plain text with Vinegere cipher advanced:
Let�s take a plain text: �DOTNETSPIDER IS A LEADING WEBSITE FOR DOT NET COMMUNITY� and we want to encrypt the plain text using �Vigenere Cipher�, using key/password as �PAUL� and alphabet key as �SPIDER�.
So our plain text�s cipher/encrypted text will become: �EXKERZUMDFYT DA S IRJXNON NQCAWBR MHT EXK ERZ IRNVLEDZQ�.
Do you see it�s very different from the Vinegere cipher basic�s cipher text that we derived earlier.
The process of encrypting the plain text is same as the Vinegere cipher basic (explained above).
Let�s see with an example:
Let�s take plain text as: �WEBSITE�.
The password as �PAUL�.
The alphabet key is �SPIDER�.
So from the above table only keep the sections of alphabets of �PASSWORD REFERENCE� that constitutes in the word �PAUL�(in ascending order).
That is: �P� �A�, �L�, and �U�
So the derived table would be:
Now refer �W� from the �TEXT REFERENCE� section of the table, and �P� from the �PASSWORD REFERENCE� section of the table,
Like this:
See what you get: Now replace the value of �W� with �X�
Similarly take the letter �E� from the �TEXT REFERENCE� section of the table, and �A� from the �PASSWORD REFERENCE� section of the table.
See what you get: Now replace the value of �E� with �G�
Repeating the above steps you will get �WEBSITE�, using password as �PAUL� and alphabet key as �SPIDER�, The Vigenere cipher as, �XGPLDZY�.
Now let�s go to the coding part of Vinegere cipher:
The Basic look of my app is as such:
There are two radio buttons: :Basic and "Advance".
If "Basic" is checked then:
If "Advance" is checked then:
Now the code:
On form load
private void Form1_Load(object sender, EventArgs e)
{
basicRadioButton.Checked = true;
}
private void basicRadioButton_CheckedChanged(object sender, EventArgs e)
{
label2.Visible = false;
keyTextBox.Visible = false;
}
private void advanceRadioButton_CheckedChanged(object sender, EventArgs e)
{
label2.Visible = true;
keyTextBox.Visible = true;
}
//Here I am only using characters A-Z(upper case)
//To increase the complexity of the VIGENERE CIPHER lower case"a-z", Numerics and Symbols also can be used
string alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Remove duplicate characters from "Alphabet Key" method
static string RemoveDuplicateChars(string key)
{
// --- Removes duplicate chars using string concats. ---
// Store encountered letters in this string.
string text = "";
// Store the result in this string.
string final = "";
// Loop over each character.
foreach (char value in key)
{
// See if character is in the table.
if (text.IndexOf(value) == -1)
{
if (value == ' ')
{
//do nothing
}
else
{
// Append to the table and the result.
text += value;
final += value;
}
}
}
return final;
}
Encrypt using "Vigenere Cipher"
#region Encrypt using "Vigenere Cipher"
private void encryptButton_Click(object sender, EventArgs e)
{
char encryptedChar;
string encryptedText = "";
int charIndexOfText, charIndexOfPassword, newIndex;
char charOfText;
char charOfPassword;
string table = "";
string result = "";
alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string text = richTextBox1.Text;
string password = passwordTextBox.Text;
charIndexOfText = charIndexOfPassword = newIndex = 0;
//If want to use both key and password else it will only use password
if (advanceRadioButton.Checked)
{
//Removes duplicate characters from the string "alphabets"
//For example: if the key is "MRINMAY"
//The string "alphabets" will be modified to "MRINAYBCDEFGHJKLOPQSTUVWXZ"
string key = RemoveDuplicateChars(keyTextBox.Text);
alphabets = RemoveDuplicateChars(key.ToUpper() + alphabets);
}
else// If basic radio button is selected
{
alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
}
//look for white space in the password and discard it
//it is very that, a vigenere cipher's password should not have white space
foreach (char value in password)
{
// if character is white space.
if (value == ' ')
{
//do nothing
}
else
{
// Append valid character to the table and the result.
table += value;
result += value;
}
//password without white space
password = result;
}
for (int i = 0; i < text.Length; i++)
{
for (int j = 0; j < password.Length; j++)
{
if (i < text.Length)
{
//get each character of the text and the password
//Note: I have used only Upper Case alphabets
//but if you want to include lower case alphabets, add lower case alphabets(a-z) to string "alphabets"
//replace the next two lines of code with this:/* charOfText = text[i]; charOfPassword = password[j];*/
charOfText = char.ToUpper(text[i]);
charOfPassword = char.ToUpper(password[j]);
if(charOfText == ' ')// if encounters a white space in the text
{
//add the white case character to the encrypted text
encryptedChar = charOfText;
encryptedText = encryptedText + encryptedChar;
i++;
j--;
}
else if (charOfText == '\n')// if encounters a new line in the text
{
//add the new line character to the encrypted text
encryptedChar = charOfText;
encryptedText = encryptedText + encryptedChar;
i++;
j--;
}
else
{
//Get the index of the character of text from alphabets variable
charIndexOfText = alphabets.IndexOf(charOfText);
//Get the index of the character of password from alphabets variable
charIndexOfPassword = alphabets.IndexOf(charOfPassword);
//Get the encrypted character
newIndex = (charIndexOfText + charIndexOfPassword) % 26;
encryptedChar = alphabets[newIndex];
//add the encrypted character to a string every time to get an encrypted string
encryptedText = encryptedText + encryptedChar;
i++;
}
}
}
i--;
}
//Display Encrypted text
richTextBox1.Clear();
richTextBox1.Text = encryptedText;
}
#endregion
Decrypt using "Vigenere Cipher"
#region Decrypt using "Vigenere Cipher"
private void Decrypt_Click(object sender, EventArgs e)
{
char newChar;
string encryptedText = richTextBox1.Text;
string decryptedText = "";
int charIndexOfEncryptedText, charIndexOfPassword, newIndex;
char charOfEncryptedText;
char charOfPassword;
string table = "";
string result = "";
alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string password = passwordTextBox.Text;
charIndexOfEncryptedText = charIndexOfPassword = newIndex = 0;
//If want to use both key and password else it will only use password
if (advanceRadioButton.Checked)
{
//Removes duplicate characters from the string "alphabets"
//For example: if the key is "MRINMAY"
//The string "alphabets" will be modified to "MRINAYBCDEFGHJKLOPQSTUVWXZ"
string key = RemoveDuplicateChars(keyTextBox.Text);
alphabets = RemoveDuplicateChars(key.ToUpper() + alphabets);
}
else// If basic radio button is selected
{
alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
}
//look for white space in the password and discard it
//it is very that, a vigenere cipher's password should not have white space
foreach (char value in password)
{
// See if character is in the table.
if (value == ' ')
{
//do nothing
}
else
{
// Append valid character to the table and the result.
table += value;
result += value;
}
//password without white space
password = result;
}
for (int i = 0; i < encryptedText.Length; i++)
{
for (int j = 0; j < password.Length; j++)
{
if (i < encryptedText.Length)
{
//get each character of the encrypted text and the password
//Note: I have used only Upper Case alphabets
//but if you want to include lower case alphabets, add lower case alphabets(a-z) to string "alphabets"
//replace the next two lines of code with this:/* charOfText = encryptedtext[i]; charOfPassword = password[j];*/
charOfEncryptedText = char.ToUpper(encryptedText[i]);
charOfPassword = char.ToUpper(password[j]);
if (charOfEncryptedText == ' ')// if encounters a white space in the encrypted text
{
//add the white case character to the decrypted text
newChar = charOfEncryptedText;
decryptedText = decryptedText + newChar;
i++;
j--;
}
else if (charOfEncryptedText == '\n')// if encounters a new line in the encrypted text
{
//add the new line character to the decrypted text
newChar = charOfEncryptedText;
decryptedText = decryptedText + newChar;
i++;
j--;
}
else
{
//Get the index of the character of encrypted text from alphabets variable
charIndexOfEncryptedText = alphabets.IndexOf(charOfEncryptedText);
//Get the index of the character of password from alphabets variable
charIndexOfPassword = alphabets.IndexOf(charOfPassword);
newIndex = (charIndexOfEncryptedText - charIndexOfPassword) % 26;
//if the character is at the start of the string "alphabets"
if ((charIndexOfEncryptedText - charIndexOfPassword) < 0)
{
//Get the decrypted character
newChar = alphabets[newIndex + 26];
//add the decrypted character to a string every time to get an encrypted string
decryptedText = decryptedText + newChar;
i++;
}
else
{
//Get the decrypted character
newChar = alphabets[newIndex];
//add the decrypted character to a string every time to get an decrypted string
decryptedText = decryptedText + newChar;
i++;
}
}
}
}
i--;
}
richTextBox1.Clear();
richTextBox1.Text = decryptedText;
}
#endregion
End of Vigenere cipher advance
******************************************
Note: In the above examples I have only used upper case English alphabets (A-Z).
You can use lower case alphabets(a-z), numerics(0-9) and symbols to increase the complexity of the ciphers.
************** THE END ******************
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