Monday, December 4, 2023

How TOPT Works: Generating OTPs Without Internet Connection


Have you ever wondered how authentication apps like RSA Authenticator generate One-Time Passwords (OTPs) without requiring an internet connection? This fascinating technology is made possible through Time-Based One-Time Passwords (TOTP). In this article, we will explore the mechanics of TOTP, its security features, and why it doesn't rely on the internet at the client-side for generating OTPs.

Understanding TOPT

1. TOPT in a Nutshell

TOPT, or Time-Based One-Time Password, is a security feature designed to enhance the authentication process. It generates OTPs that are only valid for a short period, typically 30 seconds. TOPT uses a secret key, often shared between the server and the user's device, to generate these OTPs. The central idea is to provide a second factor of authentication, beyond just a static password, to strengthen security.

2. The RSA Authenticator App

One popular example of a TOPT implementation is the RSA Authenticator app. This app is commonly used for two-factor authentication and generates OTPs even when the device is offline. So, how does it work?

The Inner Workings of TOPT

1. Secret Key and Initialization

When setting up TOPT on a device, the user and the authentication server share a secret key. This key is securely stored on both sides and is crucial for generating the OTPs. The server also maintains a counter that increments every 30 seconds.

2. Time-Step and Hashing

To generate an OTP, the device combines the secret key with a time-step value. This time-step value is derived from the current time, typically using Unix time (the number of seconds since January 1, 1970). The resulting value is then hashed, often using the HMAC-SHA1 algorithm.

3. Presentation of OTP

The resulting hash is typically a 160-bit value, which is then truncated to obtain a 6 to 8 digit OTP. The truncation involves taking a subset of bits from the hash. The number of digits and the specific bits selected are implementation-dependent.

4. Rolling Code

The server, which is aware of the current time and the shared secret key, can perform the same process to generate an OTP. If the generated OTP matches the one presented by the user, access is granted.

Advantages of TOPT

1. Offline OTP Generation

One of the major advantages of TOPT is that it does not require an internet connection to generate OTPs. The algorithm is based on a predefined time-step, allowing the device and the server to independently generate OTPs at the same time. This is particularly useful when an internet connection is unavailable, ensuring users can still access their accounts securely.

2. Enhanced Security

TOPT significantly enhances security because the OTPs are time-bound and change frequently. Even if an attacker intercepts an OTP, it will be invalid within seconds, reducing the risk of unauthorized access.

TOTP: A Special Case of TOPT

1. What is TOTP?

TOTP, or Time-Based One-Time Password, is a specific implementation of TOPT. It uses the current time as the input for generating OTPs. TOTP ensures that OTPs are synchronized between the device and the server, allowing for secure authentication even when offline.

2. TOTP in Action

In TOTP, the user and the server share a secret key. The device and the server independently generate OTPs based on the current time. The time-step is typically set to 30 seconds, ensuring that OTPs remain valid for a short period.


TOPT, and specifically TOTP, play a crucial role in modern authentication systems. They provide an additional layer of security by generating time-bound OTPs, without requiring an internet connection at the client-side. This capability ensures that even when internet access is unavailable, users can still access their accounts securely. The use of secret keys and time-based calculations makes TOPT a robust and widely adopted security feature, strengthening the overall security of online services.

Demystifying Service Mesh: How it Works and Why You Need It


In the ever-evolving landscape of modern application development and deployment, the concept of a "Service Mesh" has gained significant traction. As a tech blogger with over 12 years of experience, I'm here to provide a comprehensive update on this crucial topic. In this article, we'll delve into what a Service Mesh is, how it works, and why it has become an indispensable tool for managing complex microservices architectures.

What is a Service Mesh?

A Service Mesh is a dedicated infrastructure layer designed to facilitate communication between the microservices that make up an application. It acts as a transparent, language-agnostic network of interconnected components, providing essential functionalities such as service discovery, load balancing, security, and observability. The primary goal of a Service Mesh is to enhance the reliability, security, and manageability of microservices-based applications.

How Does it Work?

Now, let's dive deeper into how a Service Mesh actually works:

  1. Sidecar Proxy: At the heart of a Service Mesh, you'll find a sidecar proxy. Every microservice in the application is paired with its own proxy, effectively forming a "sidecar." These sidecar proxies are responsible for intercepting all inbound and outbound network traffic to and from the microservice they are attached to.
  2. Service Discovery: When a microservice needs to communicate with another service, it queries the Service Mesh for the location of the target service. The Service Mesh provides dynamic service discovery, ensuring that services can locate each other regardless of their changing IP addresses or locations.
  3. Load Balancing: Service Meshes implement sophisticated load balancing algorithms, distributing incoming requests evenly across instances of a service. This helps in optimizing resource utilization and ensuring high availability.
  4. Security: Security is a top priority in microservices architectures. Service Meshes offer robust security features like mutual TLS (mTLS) encryption, authentication, and authorization. With mTLS, all communication between microservices is encrypted and authenticated, significantly enhancing the overall security posture.
  5. Traffic Management: Service Meshes allow for fine-grained traffic control and routing. This means you can implement A/B testing, canary releases, and gradual rollouts with ease, all while monitoring the impact on your application's performance and stability.

Observability and Monitoring: Service Meshes provide rich observability features, including metrics, logging, and tracing. This enables DevOps teams to gain deep insights into the behavior of their microservices and diagnose issues quickly.

Why You Need a Service Mesh:

Now, you might wonder why Service Meshes have gained such popularity. Here are a few key reasons:

  1. Microservices Complexity: As applications become more microservices-oriented, managing the complexity of service-to-service communication becomes increasingly challenging. Service Meshes provide a centralized solution for handling this complexity.
  2. Resilience and Reliability: With features like load balancing, circuit breaking, and automatic retries, Service Meshes improve the overall resilience of your application. They can handle failures gracefully, reducing downtime and improving user experience.
  3. Security: Service Meshes enhance the security of your microservices by implementing encryption and authentication. This is crucial, especially in multi-cloud or hybrid cloud environments.
  4. Observability: The ability to monitor and troubleshoot your microservices is essential for maintaining high availability and performance. Service Meshes offer a wealth of observability tools that simplify this process.


In the world of modern application development, a Service Mesh has become more of a necessity than a luxury. It offers a unified solution for managing the complexities of microservices architectures, ensuring reliability, security, and observability. 

How TOPT Works: Generating OTPs Without Internet Connection

Introduction Have you ever wondered how authentication apps like RSA Authenticator generate One-Time Passwords (OTPs) without requiring an i...