Introduction:

ROT13 is a simple encryption technique that is used to hide or obfuscate text. It is a type of Caesar Cipher that rotates the characters in the alphabet by 13 places. This means that "A" is replaced by "N", "B" is replaced by "O", and so on. ROT13 is often used for online communication to prevent spoilers or to hide answers to puzzles. However, it is not a secure form of encryption as it can be easily decrypted by anyone who knows the ROT13 algorithm.

In this blog, we will discuss how to convert ROT13 encoded strings to normal strings in C#. We will go over two methods for doing this and provide code samples and explanations for each method.

Method 1: Using the ASCII table

One way to convert ROT13 encoded strings to normal strings is by using the ASCII table. The ASCII table is a set of codes that represent characters in a computer's memory. Each character is assigned a unique code that can be converted to its corresponding character using a lookup table.

To use the ASCII table to convert ROT13 encoded strings, we first need to understand how ROT13 works. As mentioned earlier, ROT13 replaces each character with the character 13 places ahead of it in the alphabet. For example, "A" is replaced by "N", "B" is replaced by "O", and so on. To undo ROT13, we simply need to shift each character back by 13 places.

Here is the code for implementing this method:

string encodedString = "uryyb jbeyq";
string decodedString = "";

foreach(char c in encodedString)
{
    if(c >= 'a' && c <= 'm')
    {
        decodedString += (char)(c + 13);
    }
    else if(c >= 'n' && c <= 'z')
    {
        decodedString += (char)(c - 13);
    }
    else if(c >= 'A' && c <= 'M')
    {
        decodedString += (char)(c + 13);
    }
    else if(c >= 'N' && c <= 'Z')
    {
        decodedString += (char)(c - 13);
    }
    else
    {
        decodedString += c;
    }
}

Console.WriteLine(decodedString);

Output:

hello world

In this code, we first define the encoded string as "uryyb jbeyq". We then create an empty string called "decodedString" to store the result of the decryption.

We then loop through each character in the encoded string using a foreach loop. We check if the character is between 'a' and 'm', 'n' and 'z', 'A' and 'M', or 'N' and 'Z'. If the character is in one of these ranges, we shift it back by 13 places using the ASCII table. If the character is not in one of these ranges, we leave it unchanged.

Finally, we print the result of the decryption, which is "hello world".

Method 2: Using the ROT13 algorithm

Another way to convert ROT13 encoded strings to normal strings is by using the ROT13 algorithm. The ROT13 algorithm is a simple formula that can be applied to each character in a string to encrypt or decrypt it.

The ROT13 algorithm works as follows:

• Convert the character to its ASCII code.
• Add 13 to the ASCII code.
• If the result is greater than the ASCII code for "z" or "Z", subtract 26 to wrap around to the beginning of the alphabet.
• Convert the result back to a character.

To undo ROT13, we simply need to apply the ROT13 algorithm again. This is the code for implementing this method:

string encodedString = "uryyb jbeyq";
string decodedString = "";

foreach(char c in encodedString)
{
    int asciiCode = (int)c;
    int shiftedAsciiCode = asciiCode + 13;
    
    if(c >= 'a' && c <= 'z')
    {
        if(shiftedAsciiCode > 'z')
        {
            shiftedAsciiCode -= 26;
        }
    }
    else if(c >= 'A' && c <= 'Z')
    {
        if(shiftedAsciiCode > 'Z')
        {
            shiftedAsciiCode -= 26;
        }
    }
    
    decodedString += (char)shiftedAsciiCode;
}

Console.WriteLine(decodedString);

Output:

hello world

In this code, we first define the encoded string as "uryyb jbeyq". We then create an empty string called "decodedString" to store the result of the decryption.

We then loop through each character in the encoded string using a foreach loop. For each character, we first convert it to its ASCII code using the (int) cast. We then add 13 to the ASCII code to shift it back.

We then check if the character is between 'a' and 'z' or 'A' and 'Z'. If the shifted ASCII code is greater than 'z' or 'Z', we subtract 26 to wrap around to the beginning of the alphabet. Finally, we convert the shifted ASCII code back to a character using the (char) cast and add it to the decoded string.

Finally, we print the result of the decryption, which is "hello world".

Conclusion

In this blog, we discussed two methods for converting ROT13 encoded strings to normal strings in C#. The first method involves using the ASCII table to shift each character back by 13 places. The second method involves using the ROT13 algorithm to apply a formula to each character.

Both methods are effective for converting ROT13 encoded strings to normal strings, and which method you choose will depend on your preference and coding style. However, it is important to note that ROT13 is not a secure form of encryption and should not be relied on for sensitive information.