How do you design and implement a scalable and secure hash-based authentication system?

1 What is hashing and why is it important?

Hashing is a process of transforming any data into a fixed-length string of characters, called a hash or a digest, using a mathematical function, called a hash function. Hashing has two main properties: it is irreversible and collision-resistant. This means that you cannot recover the original data from the hash, and it is very unlikely that two different data will produce the same hash. Hashing is important for authentication because it allows you to store and compare hashes of passwords instead of plain text passwords, which are vulnerable to theft and cracking.

2 How to choose a hash function and a salt?

A hash function is a key component of your authentication system, as it determines how secure and efficient your hashing is. You should choose a hash function that is fast, consistent, and resistant to attacks, such as brute force, rainbow tables, and length extension. Some examples of hash functions that are widely used for authentication are SHA-256, SHA-3, and bcrypt. A salt is a random value that is added to the data before hashing, to prevent pre-computed attacks and increase the entropy of the hashes. You should choose a salt that is long, unique, and random for each data, and store it along with the hash.

3 How to generate and store hashes and salts?

To generate a hash and a salt for a password, you can use a library or a tool that implements your chosen hash function and provides a method to generate a salt. For example, in Python, you can use the hashlib or the bcrypt module to hash a password with SHA-256 or bcrypt, respectively, and generate a salt. To store the hashes and salts, you can use a database or a file system that is secure, reliable, and scalable. You should store the hash and the salt together, either as a single string or as separate fields, and use a delimiter or a format to distinguish them.

4 How to verify hashes and authenticate users?

To verify a hash and authenticate a user, you need to compare the hash of the user's input password with the stored hash of the user's registered password. To do this, you need to retrieve the stored hash and the salt from the database or the file system, extract the salt from the hash or the separate field, append it to the input password, hash it with the same hash function, and compare the resulting hash with the stored hash. If they match, the user is authenticated; otherwise, the user is rejected.

5 How to update hashes and salts?

To update a hash and a salt for a password, you need to generate a new hash and a new salt for the new password, and replace the old hash and salt with the new ones in the database or the file system. You should update a hash and a salt whenever a user changes their password, or when you want to upgrade your hash function or your salt length. Updating hashes and salts regularly can improve the security and performance of your authentication system.

6 How to handle errors and exceptions?

To handle errors and exceptions in your authentication system, you need to implement some error handling mechanisms and logging functions. For example, you should catch any exceptions that may occur when hashing, storing, retrieving, or comparing hashes and salts, such as invalid input, database errors, or hash function errors, and return appropriate messages or codes to the user or the system. You should also log any errors or exceptions that occur, along with relevant information, such as timestamps, user IDs, hash functions, and salts, for debugging and auditing purposes.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?