Authentication and Authorization
The Ultimate Guide to Authentication & Authorization
Understanding Authentication & Authorization: A Journey from Handshakes to Hashing
We encounter it every single day. From logging into our favorite social media apps to accessing our work platforms, the gates of digital entry are guarded by two crucial concepts: authentication and authorization. While often used interchangeably, they serve distinct but equally vital roles in securing our online experiences.
Let's break them down:
Authentication: Simply put, authentication answers the question, "Who are you?" It's the process of verifying your identity, proving that you are indeed who you claim to be. Think of it as showing your ID to get into a club.
Authorization: Once your identity is confirmed, authorization steps in to answer, "What can you do?" It determines your permissions and capabilities within that system. After showing your ID, authorization dictates whether you're allowed on the dance floor, at the VIP table, or just by the entrance.
To truly appreciate the sophisticated systems we use today, let's embark on a fascinating journey through the history and evolution of these fundamental security pillars.
A Glimpse into the Past: How We Proved "Who We Are"
The need to verify identity isn't new; it's evolved dramatically over centuries:
Pre-Industrial Societies: The Era of Trust In early communities, authentication was intrinsic. Identity was synonymous with recognition. A respected village elder might vouch for someone, and agreements were sealed with a handshake. This system relied heavily on human trust within familiar circles, but it simply couldn't scale beyond the village.
Medieval Period: The Rise of the Seal As societies grew, explicit proof of identity became necessary. Enter the wax seal! These unique patterns pressed onto documents served as early "authentication tokens." Possession of the correct seal signified identity and agreement. However, these physical tokens were vulnerable to forgery, leading to the earliest "authentication bypass attacks." This spurred the initial thoughts on more robust "cryptographic" methods.
Industrial Revolution: Passphrases and Shared Secrets The advent of technologies like the telegraph demanded secure communication. Telegraph operators began using pre-agreed "passphrases" – static strings of words known only to authorized individuals. This marked a significant shift: from "something you possess" (the seal) to "something you know" (the passphrase), a direct ancestor of our modern passwords.
Mid-20th Century: The Digital Dawn With the emergence of mainframes and multi-user computer systems, authentication entered its digital phase. Researchers at MIT's Project Mac, in 1961, introduced the concept of passwords for multi-user systems. A critical early vulnerability – passwords being stored in plain text – led to a pivotal moment when a password file was printed. This incident became the catalyst for the philosophy of secure password storage, giving birth to techniques like hashing and various cryptographic algorithms that transform passwords into irreversible, fixed-length representations. This era also saw the core tenets of information security – confidentiality, integrity, and availability – begin to align with authentication principles.
The 1970s: Cryptographic Breakthroughs The invention of the Diffie-Hellman key exchange revolutionized cryptography by introducing asymmetric cryptography. This groundbreaking technique allowed two parties to establish a shared secret over an untrusted medium, becoming the bedrock of modern authentication protocols, including Public Key Infrastructure (PKI) systems. Protocols like Kerberos, introducing ticket-based authentication, also emerged as precursors to today's token-based systems.
The 1990s: Multi-Factor Authentication (MFA) As the internet exploded, simple username/password systems proved too weak against evolving threats like brute-force and dictionary attacks. The solution? Multi-Factor Authentication (MFA). This powerful approach combines multiple independent verification factors:
Something you know: Passwords, PINs.
Something you have: Smart cards, OTP (One-Time Password) generators.
Something you are: Biometric data (fingerprints, retina scans). MFA significantly boosted security by requiring more than one piece of evidence for identity verification.
The 21st Century: The Modern Landscape The rise of cloud computing, mobile devices, and API-driven architectures demanded even more advanced and flexible authentication frameworks. This led to the development of technologies we commonly use today:
OAuth and OAuth 2.0: Industry-standard protocols for delegated authorization.
JWTs (JSON Web Tokens): Lightweight, self-contained tokens.
Zero Trust Architecture: A security model where no user or device is trusted by default.
Passwordless Authentication (WebAuthn): Eliminates passwords entirely by leveraging public/private key pairs stored on hardware devices.
Looking Ahead: The Future of Identity The journey continues with promising candidates for the future of authentication:
Decentralized Identity: Leveraging blockchain technology for self-sovereign identity.
Behavioral Biometrics: Analyzing unique user behaviors for continuous authentication.
Post-Quantum Cryptography: Developing cryptographic techniques resistant to future quantum computing attacks, which could potentially break current encryption standards.
Diving Deep: The Technical Backbone of Modern Authentication
Now, let's explore two critical components that power most modern authentication workflows: Sessions and JWTs.
Sessions: Giving the Web a Memory
When the web first emerged, the underlying HTTP protocol was designed to be stateless. This meant every request from your browser to a server was treated as an isolated interaction; the server had no memory of your previous actions. While ideal for static pages, this statelessness became a huge bottleneck as the web transitioned to dynamic, interactive content like e-commerce sites (imagine trying to keep items in a shopping cart if the server "forgot" you with every click!).
This is where sessions came to the rescue, providing a way to establish a temporary server-side context for each user, essentially giving the server a "memory" about you.
How Sessions Work:
Session Creation: When you successfully log in, the server generates a unique session ID and stores it along with user data (like roles and permissions) in a persistent store (often Redis or a database).
Session ID Transmission: The server sends this session ID back to your browser, typically embedded within a cookie.
Subsequent Requests: For every subsequent request you make, your browser automatically includes this cookie, sending the session ID back to the server. The server then uses this ID to retrieve your associated data from its persistent store, allowing it to "remember" you and maintain your logged-in state or shopping cart contents across pages.
Sessions were a monumental step, enabling the interactive web we know today.
JWTs (JSON Web Tokens): The Rise of Stateless Tokens
By the mid-2000s, as web applications became globally distributed and scaled to millions of users, stateful session management started to face new challenges:
Memory Overhead: Maintaining session data for vast numbers of users became costly.
Replication Complexity: Synchronizing session data across multiple distributed servers and regions introduced latency and consistency issues.
Developers sought a solution that could offload state from the server while maintaining security. The answer arrived with JWTs (JSON Web Tokens), formalized in 2015.
The Power of Statelessness:
The key innovation of JWTs is their self-contained, stateless nature. A JWT itself carries all the necessary user data and a cryptographic signature, eliminating the need for the server to constantly look up user information in a separate session store.
What Does a JWT Look Like? A typical JWT is a long, base64-encoded string divided into three parts by dots:
Header: Contains metadata about the token itself, such as the signing algorithm used (e.g.,
HS256).Payload (Claims): This is the heart of the JWT, containing "claims" or statements about the user. Common claims include:
sub(subject): Typically the user's unique ID.iat(issued at): The timestamp when the JWT was created.Optional custom claims: User's name, role (e.g., "admin," "editor"), etc.
Signature: This is a cryptographic hash created using the header, payload, and a secret key known only to the server. The signature is crucial for verifying that the token hasn't been tampered with and was indeed issued by the legitimate server.
How JWTs Work: When a user logs in, the server creates a JWT, signs it with its secret key, and sends it to the client. The client stores this JWT (e.g., in local storage or a cookie). For subsequent requests, the client includes the JWT in the authorization header. The server then receives the JWT, verifies its signature using the same secret key, and can immediately access the user's data from the payload without any additional database lookups.
Advantages of JWTs:
Statelessness: No server-side session storage needed, reducing memory footprint and complexity.
Scalability: In distributed microservice architectures, different services can independently validate JWTs using a shared secret key, simplifying authentication across multiple instances.
Portability: Their compact, URL-friendly format makes them easy to transmit and store in various environments.
Challenges of JWTs:
Token Theft: If a JWT is intercepted, an attacker can use it to impersonate the user until the token expires, as there's no inherent server-side mechanism to invalidate it.
Revocation: Instantly revoking a specific user's access can be tricky with purely stateless JWTs. Changing the secret key would invalidate all active tokens, forcing every user to re-authenticate.
Beyond the Basics: Advanced Authentication Strategies & When to Use Them
The JWT Dilemma: Statelessness vs. Control
While JWTs are lauded for their statelessness, a fundamental question arises: What if you need to revoke a user's access immediately? If a user's account is compromised, you can't just invalidate their JWT because, by design, it's stateless. The server doesn't "remember" it. The only way to revoke it directly would be to change the secret key used to sign all JWTs, which would log out every single user – a major inconvenience.
This is where the concept of a hybrid approach comes in. Many systems combine the best of both worlds:
A user logs in and receives a JWT.
For every subsequent request, the client sends the JWT (often in an
Authorizationheader).The server verifies the JWT's signature.
Crucially, the server then performs an additional lookup in a persistent store (like Redis) to check a blacklist of revoked tokens. If the JWT is on the blacklist, access is denied.
This approach gives you the ability to revoke specific tokens in real-time, addressing a major drawback of pure stateless JWTs.
But wait, if you're doing a persistent storage lookup anyway, why not just stick to stateful sessions in the first place? This is a valid question that often sparks debate in the industry. The answer usually lies in the specific trade-offs for your application's scale, architecture, and security needs.
The Pragmatic Path: Embrace Authentication Providers
For many, the complexity of implementing and maintaining a secure authentication system from scratch is simply not worth the risk. This is why the industry often advises: don't build your own authentication unless you absolutely have to.
Instead, consider using an external authentication provider. Services like Auth0, Clerk, Okta, and many others specialize in handling the intricate details of authentication and authorization. They take on the burden of:
Implementing secure hashing and salting of passwords.
Managing session lifecycle and token revocation.
Handling multi-factor authentication (MFA).
Keeping up with the latest security best practices and vulnerabilities.
Providing flexible authentication flows (social logins, enterprise SSO, etc.).
For medium to large-scale systems, offloading this critical component to experts is often the most secure and efficient path. While it's invaluable for backend engineers to understand the underlying mechanisms (and implementing your own for learning is highly recommended!), deploying a production system typically benefits greatly from a dedicated authentication provider.
Cookies: The Unsung Heroes of Web State
Before diving into different authentication types, it's essential to understand cookies. We've already mentioned them in the context of sessions, but let's clarify their role.
A cookie is a small piece of information that a server can store in your web browser. When you visit a website, the server can set a cookie. Crucially, your browser will then automatically send this cookie back to that same server with every subsequent request.
This seemingly simple mechanism is incredibly powerful:
Automated Token Handling: When a user authenticates, the server can set a cookie containing a session ID or a JWT. Your browser then handles sending this cookie with future requests, automating the process of maintaining your logged-in state without you (or the client-side JavaScript) needing to explicitly manage the token.
Security Features: Browsers enforce strict security measures for cookies. For instance, a cookie set by one server generally cannot be accessed by another server, protecting your data. HTTP-only cookies are particularly secure, as they prevent client-side JavaScript from accessing their values, mitigating certain types of attacks.
Deep Dive: Authentication Types
With cookies and the JWT/Session discussion in mind, let's categorize the major authentication types backend engineers encounter:
1. Stateful Authentication (e.g., Sessions)
This is the traditional approach, where the server maintains a "state" about the user's session.
How it Works:
The client sends a username and password to the server.
If credentials are valid, the server generates a unique session ID and stores it along with user data (like roles and permissions) in a persistent store (often Redis or a database).
The server sends this session ID back to the client, usually embedded in an HTTP-only cookie.
For all subsequent requests, the browser automatically sends the cookie containing the session ID.
The server receives the cookie, looks up the session ID in its store, retrieves user data, and validates the session (e.g., checks expiry).
Pros:
Centralized Control: The server has real-time information about all active sessions, making it easy to revoke a session (e.g., force a user logout) at any time.
Simpler Revocation: Direct control over sessions makes revoking access straightforward.
Well-suited for traditional web applications with moderate to high traffic and strict session management needs.
Cons:
Scalability Challenges: In large, distributed systems, synchronizing session data across multiple servers can introduce latency and complexity.
Higher Operational Overhead: Requires managing and maintaining a dedicated session store.
When to Use: Most applications that prioritize real-time session control and operate within a moderately distributed environment. Often recommended as a default for robust web applications.
2. Stateless Authentication (e.g., JWTs)
This approach ensures the server does not store any session-related data after the initial authentication.
How it Works:
The client sends a username and password to the server.
If credentials are valid, the server generates a signed JWT (containing user ID, role, etc.) using a secret key.
The server sends the JWT back to the client.
For all subsequent requests, the client sends the JWT (typically in an
Authorizationheader).The server receives the JWT and verifies its signature using the secret key. If valid, the user's identity is confirmed, and the request is processed. No database lookup is needed for basic authentication.
Pros:
High Scalability: No session store dependency means horizontal scaling is simple – any server can validate any JWT.
No Session Storage Costs: Reduces server resource usage.
Ideal for Distributed Architectures: Particularly microservices, where different services can independently validate tokens.
Mobile-Friendly: JWTs can be easily stored and transmitted in mobile apps where traditional cookies might be less suitable.
Cons:
Complex Token Revocation: As discussed, revoking an individual token before its expiry is not straightforward without a hybrid approach (e.g., blacklisting). This is a significant security concern if a token is compromised.
No Real-time Session Information: The server doesn't have an immediate view of all active tokens.
When to Use: Highly distributed systems, APIs consumed by various clients (web, mobile, third-party), or scenarios where scalability and simplicity are paramount, provided you have a strategy for revocation (e.g., short-lived tokens, refresh tokens, or blacklisting).
3. API Key-Based Authentication
API keys cater to a very specific set of use cases, primarily for machine-to-machine communication.
How it Works:
A platform user (e.g., in a UI) generates an API key – a long, cryptographically random string.
This API key is then used programmatically by another application or server to access the platform's services. The key is typically sent in a request header.
The server validates the API key, often by looking it up in a database to check its validity, associated permissions, and expiry.
Primary Use Case: Programmatic Access (Machine-to-Machine) Imagine you're building an application that needs to use ChatGPT's capabilities to summarize user input. Your server (a "machine") needs to communicate with OpenAI's server (another "machine"). You wouldn't log into OpenAI's UI with a username and password from your server. Instead, you'd generate an API key and include it with your programmatic requests. This key identifies your application and its allowed actions (e.g., making text generation calls).
Pros:
Simple to Generate and Use: Easy for users to obtain and integrate into their code.
Ideal for Machine-to-Machine Communication: Perfect for servers interacting with other servers or for third-party integrations.
Granular Permissions: API keys can be issued with specific permissions and expiry dates, limiting what the consuming application can do.
No Human Interaction Needed: Unlike username/password flows, API keys don't require manual login forms.
Cons:
Key Management: Requires secure storage and rotation of keys.
Not for Human Users: Generally not suitable for direct user authentication in a browser-based application.
Less Dynamic: Less suited for complex, interactive user sessions compared to session or JWT-based approaches.
When to Use: Providing programmatic access to your services for other applications, third-party integrations, or internal system communication.
4. OAuth 2.0 & OpenID Connect (OIDC): Delegated Authorization & Identity Layer
The rise of numerous online platforms led to two major problems:
Password Fatigue/Security Risk: Users creating and remembering countless passwords, often reusing them, leading to widespread compromises if one platform was breached.
Delegation Problem: The need for one website or application to securely access resources on another website on behalf of the user (e.g., a travel app accessing your Gmail to scan flight tickets, or a social media app importing contacts from Google). The initial, disastrous solution was for users to share their passwords directly.
This "delegation problem" gave birth to OAuth (Open Authorization), a revolutionary idea standardizing how users can grant limited access to their resources on one platform to another, without sharing their password.
OAuth 1.0 (The Pioneer): Developed around 2007, OAuth 1.0 introduced the concept of sharing tokens instead of passwords. These tokens had specific permissions, unlike passwords which granted full account access.
Key Components:
Resource Owner: The user who owns the data (e.g., you).
Client: The application requesting access (e.g., a social media app).
Resource Server: The server holding the resources (e.g., Google's server with your contacts).
Authorization Server: The server that authenticates the user and issues the access token.
Basic Flow (Simplified):
The Client (e.g., Facebook) redirects the Resource Owner (you) to the Authorization Server (e.g., Google's login page).
You authenticate with the Authorization Server (Google) and grant permission to the Client (Facebook) for specific resources (e.g., "read contacts").
The Authorization Server sends an access token back to the Client.
The Client uses this access token to make requests to the Resource Server (Google) to access your authorized resources (your contacts).
OAuth 1.0 beautifully solved the problem of secure delegated authorization, but it had limitations, primarily its complexity for developers and reliance on error-prone cryptographic signatures.
OAuth 2.0 (The Evolution): Released around 2010, OAuth 2.0 streamlined the protocol, making it simpler to implement and more flexible.
Key Improvements:
Introduced simpler Bearer Tokens (if you have the token, you're the bearer, and it grants access).
Offered different authorization flows tailored for various application types:
Authorization Code Flow: For server-side web apps (most secure).
Implicit Flow: For browser-based apps (now largely discouraged due to security risks).
Client Credentials Flow: For machine-to-machine communication (no user involvement).
Device Code Flow: For input-limited devices like Smart TVs.
The Missing Piece: OpenID Connect (OIDC) While OAuth 2.0 was excellent for authorization (what you can do), it didn't directly address authentication (who you are). It told the client that you granted access to certain resources, but not definitively who you were.
In 2014, OpenID Connect (OIDC) emerged, built directly on top of OAuth 2.0's security mechanisms to fill this gap.
How OIDC Extends OAuth 2.0: OIDC introduces the ID Token, which is typically a JWT. This ID token contains verifiable information about the authenticated user (e.g., user ID, when they logged in, the issuing authority).
Purpose: OIDC provides an identity layer on top of OAuth 2.0, allowing clients to verify the identity of the end-user based on the authentication performed by an Authorization Server, as well as to obtain basic profile information about the end-user.
OpenID Connect in Action: The "Sign in with Google" Experience
You've undoubtedly seen the "Sign in with Google," "Sign in with Facebook," or "Sign in with Discord" buttons across countless websites. These widely used features are powered by OpenID Connect (OIDC) behind the scenes.
How "Sign in with Google" Works (OIDC Workflow):
Initiate Login: You visit a new platform (e.g., a note-taking app, let's call it "Client"). You click "Sign in with Google."
Redirection to Authorization Server: The Client redirects your browser to Google's Authorization Server (Google's login page).
User Authentication & Consent: You log in to your Google account directly on Google's secure server. Google then asks you to grant specific permissions to the Client (e.g., allow the note-taking app to read your email, name, or profile picture).
Authorization Code & ID Token Issued: Upon successful authentication and your consent, Google's Authorization Server sends two crucial pieces of information back to the Client:
An Authorization Code: A temporary, single-use code.
An ID Token: This is a JWT that contains your verified identity information (your Google User ID, name, email, profile picture URL, etc.).
Token Exchange (Back-channel): The Client (note-taking app) receives the Authorization Code. It then uses this code to make a secure, direct (back-channel) request to Google's Authorization Server.
Access Token & (Optional) ID Token Received: In exchange for the Authorization Code, the Client receives:
An Access Token: This token is what the Client will use to access specific resources on your behalf at Google's Resource Server (e.g., your Google Keep notes, if permission was granted).
An ID Token (if not received in step 4 or if a fresh one is requested).
Now, the note-taking app has:
Your identity information from the ID Token (e.g., your Google email and name) to authenticate you on its own platform.
An Access Token that allows it to perform specific actions on your behalf with Google's services (e.g., fetching your Google Keep notes, if you granted that permission).
This entire flow ensures that the note-taking app never sees your Google password, yet it can authenticate you and access authorized resources on your behalf.
Together, OAuth 2.0 and OpenID Connect act as the digital age's security guards and key makers. They ensure that no user or platform gains more access than explicitly granted, transforming the internet from a "password-sharing chaos" into a secure, modern, and interconnected system. These technologies enable the seamless integrations and resource sharing we often take for granted today.
When to Use Which Authentication Type: A Practical Guide
Now that we've covered the four major types of authentication, how do you decide which one to use? Here are some general guidelines:
Stateful Authentication (Sessions):
Ideal for: Traditional web applications and SaaS (Software as a Service) models where user-specific session data is stored and managed on the server.
Example: Most standard web dashboards, e-commerce sites where real-time user session control (like forcing logout) is important.
Stateless Authentication (JWTs):
Ideal for: APIs, highly scalable systems with distributed servers (e.g., microservices), and mobile-friendly applications where tokens can carry user information without server-side lookups for every request.
Example: REST APIs consumed by multiple client types (web, mobile, desktop), internal service-to-service communication where a backend service needs to identify a user.
OAuth 2.0 & OpenID Connect (OIDC):
Ideal for: Third-party integrations, providing "Sign in with [External Provider]" options (like Google, Facebook, Apple, etc.), and delegating access to user resources across different platforms.
Example: A photo editing app wanting access to your Google Photos, or any website offering social logins.
API Key-Based Authentication:
Ideal for: Server-to-server or machine-to-machine communication, and providing single-purpose client access to APIs where no human user is directly involved in the authentication flow.
Example: Your server using an OpenAI API key to access its language models, or a webhook service sending data to your application.
In most backend engineering roles, you'll primarily be working with stateful and stateless authentication for your own APIs and applications, with OAuth/OIDC being critical for integrating with external services.
Authorization: Defining What a User Can Do
While authentication answers "who you are," authorization answers the critical question: "What can you do?" It's all about defining and enforcing permissions within your system.
Let's revisit our note-taking platform example: A user logs in. They can create, delete, and update notes. Simple. But what if, as the platform creator, you have "dead zone" notes (deleted notes moved to a trash bin, permanently deleted after 30 days) that only you should be able to permanently purge or view? You might even want to grant this special "admin" capability to a few trusted colleagues, but not to all users.
The naive solution of passing a "god mode" secret string with API requests is a massive security flaw. If that string is compromised, an attacker gains complete control, able to wipe your database or tamper with user data. Moreover, managing individual "secret strings" for multiple special users quickly becomes an unscalable nightmare.
This need to provide specific permissions to specific users or groups, ensuring not everyone has the same level of access, is precisely why authorization is essential. It's about building a multi-tenant system where different user roles or organizational structures dictate varying capabilities (e.g., an admin in an organization granting read-only access to some members and read/write access to others).
Role-Based Access Control (RBAC)
One of the most famous and widely used authorization techniques you'll encounter as a backend engineer is Role-Based Access Control (RBAC).
Core Concept: Instead of assigning permissions directly to individual users, RBAC assigns permissions to roles, and then assigns those roles to users.
Examples of Roles:
User,Admin,Moderator,Editor,Viewer.Permission Granularity: Different roles are granted different sets of permissions on various resources. For instance:
Userrole: Canread,write,deletetheir own notes.Adminrole: Canread,write,deleteall notes (including other users'), andaccess"dead zone" notes.You can create custom roles and define permissions as granularly as needed (e.g., "read-only access to specific project documents").
How RBAC Works in a Workflow:
Role Assignment: When a user registers or is provisioned, the server assigns them a specific role (e.g.,
Userby default, orAdminif it's the platform creator).Role Deduction in Request: In subsequent API requests, after the user is authenticated (via a session ID, JWT, or other means), the server deduces the user's assigned role. This can be done by looking up the role information stored in their session, within their JWT, or by querying a database based on their authenticated identity.
Permission Enforcement (Middleware): This deduced role is then passed through the request lifecycle. At various points in your backend code (often in "middleware" functions), before executing business logic, the system checks if the user's role has the necessary permission for the requested action.
If a user with the
Userrole tries to access the "dead zone" notes, the system checks their permissions, finds they lack access, and sends an HTTP 403 Forbidden error.If an
Adminattempts the same, the system verifies theirAdminrole has the "access dead zone" permission and allows the operation.
RBAC provides a structured, scalable, and manageable way to control access within your applications, making it far superior to ad-hoc permission checks.
Crucial Security Considerations for Backend Engineers
Beyond understanding the "how-to," a good backend engineer must also grasp crucial security best practices, particularly regarding authentication.
1. Generic Error Messages
While user-friendly error messages are generally good, they become a security risk in authentication flows.
The Problem: Specific messages like "User not found," "Incorrect password," or "Account locked due to too many failed attempts" provide valuable clues to attackers.
"User not found" tells an attacker that a given username isn't valid, allowing them to quickly move on to the next guess.
"Incorrect password" confirms that the username is valid, narrowing the attacker's focus to just brute-forcing the password.
The Solution: Always send generic error messages for authentication failures.
Instead of specific messages, simply respond with a broad "Authentication failed." This keeps attackers guessing about whether the username was wrong, the password was wrong, or the account was locked, significantly increasing their effort and confusion.
2. Defending Against Timing Attacks
A more subtle, but potentially dangerous, vulnerability is the timing attack.
The Problem: In a typical authentication process, several steps occur sequentially:
Verify if the username exists in the database.
Check if the account is locked/suspended.
Hash the provided password and compare it to the stored hash.
The key here is that hashing a password takes a measurable amount of time, more than a simple database lookup or string comparison.
If a user provides an invalid username, the process might fail quickly at step 1.
If they provide a valid username but an incorrect password, the system proceeds to step 3, hashes the password, and then fails. This additional hashing step can introduce a tiny but consistent delay in the response time (e.g., 200 milliseconds).
Attackers, using sophisticated tools, can measure these minute differences in response times. A slightly longer response time might indicate a valid username, even if the password was wrong. This leak of information allows them to optimize their brute-force attacks, focusing on valid usernames.
The Solution: You must ensure that authentication response times are equalized regardless of where the authentication failed.
Constant-Time Operations: Use cryptographically secure constant-time comparison functions for password hashes. These functions are designed to take a consistent amount of time, regardless of whether the inputs match or not.
Simulate Response Delays: If constant-time operations aren't feasible for all parts of your flow, introduce artificial delays. For instance, if the username is not found, you could add a
time.sleep()(in Go) orsetTimeout()(in Node.js) for a fixed duration to match the expected processing time of a full password hash comparison, before sending the "Authentication failed" response. This makes it impossible for attackers to infer information based on timing differences.
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