Avoiding the 5 Mistakes Most Tutorials Make When Creating a File Encryption Tool

Why “it encrypts” doesn't equate to “it’s secure” If you want to find a tutorial for encrypting files in code, your search results will provide dozens of tutorials. Most of these tutorials will produce code that, on the surface, performs encryption. Users can provide plaintext, receive ciphertext, and the code also performs decryption. Unfortunately, the phrase “the output looks scrambled” is an unsecure way to test a program for security. These tutorials fail to incorporate security practices, which will result in these tools being rejected in real life security assessments. By identifying these mistakes, we can reason about the validity of these encryption schemes. This article covers the correct way to build a file encryption tool and the mistakes that beginner encryption tools include. These mistakes will help you learn the correct way to build an encryption tool. SecureVault (Node.js, packaged with no dependencies) is a command-line tool that is referenced throughout to help provide context to the design decisions that were made for this tool. Prerequisite mindset: When designing secure systems, always assume that the attacker knows more than you. Do you really think that your adversary will only submit the inputs you assumed they would submit? They will submit corrupted inputs, they will submit old ciphertexts, and they will do anything you thought was impossible. You need to have a secure design. You must think "what malicious inputs can I handle here?" . The goal: three guarantees, not one Before you even think about writing code, you need to know exactly what you mean by that something is secure. A good file encryption tool must provide three guarantees. Most of the tutorials that I have seen think only about the first one. Confidentiality - the attacker that steals the file should not be able to read the file. Integrity - If the attacker alters the encrypted file, you will know. Authenticity - The file can only be generated by a user that knows the passwor