Simple RNN Deciphers Code

Table of Contents

1. Overview
2. Pipeline
3. Tokenization
4. Padding
5. Define RNN
6. Postprocessing
7. Output at Every Step
8. Conclusion

Overview

In this article, we will define a simple RNN to decrypt a Caesar Cipher. If you’re not familiar with RNNs, take a look at RNN Numerical Walkthrough + Code.

Caesar Cipher

A Caesar Cipher is a cipher that encodes sentences by replacing the letters by other letters shifted by a fixed size. For example, a Caesar Cipher with a left shift value of 3 will result in the following:

Input:    ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher:   DEFGHIJKLMNOPQRSTUVWXYZABC

Notice that there is a 1-to-1 mapping for every character, where every input letter maps to the letter below it. Because of this property, we will use a character-level RNN for this cipher, although word-level RNNs may be more common in practice.

Why use an RNN?

A Caesar Cipher can be solved as a multiclass classification problem using a fully-connected feedforward neural network since each letter X maps to its cipher value Y. However, an…