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The only difference is that instead of a word being the one required parameter, it is an encoding. The decoder will take almost the exact same parameters. Now that we’ve created a custom Python affine cipher encoding, let’s create a custom decoder.

Return encoded Decoding a Custom Python Affine Cipher # take the distance from the letter 'a' as the interceptĭef custom_encode(word, m = 1, b = 0, base = 'a', return_string = False): The final optional parameter of our custom encoding is whether we want to return the list as a string or as a list. We use “a” as our base (a third optional parameter). Technically, you can subtract an ord on any character, it doesn’t have to be “a”. Note that we use ord again to get the numerical value of our characters. Then we loop through each of the characters and apply our custom affine cipher. We start by creating an empty list to hold the encoded numbers. Two of the other four parameters, m, and b represent the m and b in the linear function we talked about above. The only required parameter is the word being encoded. Four of these parameters are optional with default values. We’ll call this function, custom_encode and it takes up to five parameters.

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Now that we’ve learned how to do a basic affine cipher with ord and chr, let’s look at how to create a custom cipher. The decoded word should be the same as the one you entered.īasic Python Affine Cipher Example Creating a Custom Affine Cipher Encoding Take those numbers and plug them into the decode message.

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It then returns a series of numbers to you. The image below shows the results when we cipher the word “ego”.įirst the program will prompt us for a word, you can use any word you want. All we do is call the encode() and decode() functions.

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We’ve already included the code for testing our basic Python affine cipher above. def decode():Įncoded_list = input('What is the encoded affine cipher? ')ĭecoded = ''.join(chr(int(x)) for x in encoded_list.split(' '))ĭecode() Testing Our Basic Python Affine Cipher Program We’ll take a look at the expected behavior below. We test the decoding function for our affine cipher by simply calling it. Once we have the decoded word, we print it out and then return it for later use.

That’s why we have to use the int function to turn each number into an integer to feed to chr. However, the input function reads everything as a string. Unlike the encoding function, it asks for the encoded affine cipher – a list of numbers separated by spaces. Like the Python affine cipher encode function, it prompts the user. The decode function takes no parameters either. Opposite of the ord function is the chr function which returns a character given an ASCII value. The reason we used the ASCII value encoding with ord is simply because it’s easy to decode. Now that we’ve seen a simple encoding, let’s decode that encoding. Print('Your affine cipher encoded word: ')Įncoded = ' '.join()Įncode() Decode a Simple Affine Cipher into a String Word = input('Give a word to encode in an affine cipher: ') We test this by calling the function, which we’ll see in action later on. After getting the input from the user, we create the encoded string, print it, and return it for later use. Instead, it asks the user for a word to create an example affine cipher. This encode function takes no parameters. We simply encode each letter as its ASCII value. In this version, we use the built in ord function to get the ASCII value. To start off, we’re going to cover how to create a super basic Python affine cipher encoding.

Summary of a Python Affine Cipher ProgramĮncode a String with a Basic Affine Cipher.

How to Use a Custom Encode/Decode Affine Cipher.

Creating a Custom Python Affine Cipher Encoding.

Decode a Simple Affine Cipher into a String.

Encode a String with a Basic Affine Cipher.

We are going to use a built-in function for our first affine cipher, then create a custom encoding using the y=mx + b format. In this case, y is the encoded value, m is the scaling value, x is the distance from the value of the letter “a”, and b is a custom offset/intercept. The basic equation for an affine cipher is the same as that for a line. In this post, we’re going to look at how to code up a Python affine cipher program. I would never use this in a production environment, but it’s fun to play around with.

Like all substitution ciphers, affine ciphers have their weaknesses. It technically falls into the category of “ monoalphabetic substitution ciphers”. An affine cipher is a way to encode your words into numbers. Affine ciphers are some of the most basic cryptography methods.

Substitution cipher decoder