Zero-Network Verification · Local RFC 6238 Math

True Offline Authenticator in Chrome

Unlike SMS codes or cloud push prompts that stall when cellular reception drops or a vendor API has downtime, standard TOTP authenticators compute valid login codes purely from math. Secure TOTP Authenticator runs that calculation locally inside Chrome with zero network calls required.

Add Offline Authenticator to ChromeExplore RFC 6238 TOTP Math

Secure TOTP Authenticator is an independent browser extension developed by GreeLogix. It is not affiliated with, endorsed by, or officially connected to Google or Google Authenticator.

How TOTP Codes Work Without an Internet Connection

When people look for an offline 2FA authenticator, two separate questions are usually being asked: first, can the tool generate valid codes offline? And second, does the app upload my secrets to a remote cloud server?

Under the open IETF RFC 6238 (TOTP) specification, authentication codes do not come from an online server at login time. Instead, two inputs already present on your computer produce the answer:

1. Shared Secret Key

A Base32 string scanned from the setup QR code or typed manually once when enabling 2FA. Saved locally in Chrome.

2. Device System Clock

Current UTC epoch seconds divided by the interval (typically 30 or 60 seconds), providing a synchronized counter without network packets.

Local Calculation Pipeline (Zero Network Calls):
TimeStep = floor(UnixTimestampUTC / PeriodSeconds)
Hash = HMAC-SHA1|SHA256|SHA512(SecretKey, TimeStep)
Code = DynamicTruncate(Hash) mod 10^Digits
Chrome Extension · Inspect algorithm settings, usage metadata & secret reveal
Secure TOTP Authenticator account details view showing added date, last used time, copy count, SHA-1 6-digit 30-second parameters, and Show secret button
Inspect algorithm settings, usage metadata & secret reveal: Track when each account was added, when a code was last copied, view algorithm parameters (SHA-1/SHA-256/SHA-512), and reveal saved secrets only when needed.

What Works Completely Offline vs. What Needs Connectivity

Honest clarity matters: here is exactly when Secure TOTP works with airplane mode on, and when external actions still involve the network.

Works 100% Offline

  • Generating 6-digit and 8-digit TOTP codes continuously
  • Running SHA-1, SHA-256, and SHA-512 over 30s or 60s periods
  • Searching saved accounts and copying OTP codes in one click
  • Importing saved QR images already downloaded to disk
  • Restoring or exporting password-encrypted .json backup files
  • Inspecting saved metadata and toggling Show/Hide secrets

Requires Internet / External Access

  • First-time installation from the Chrome Web Store
  • Visiting a service's security settings page to generate a new 2FA QR
  • Authenticating into live online websites once you copy the code
  • Keeping your operating system clock reasonably synced via NTP over time
Chrome Extension · Password-protected encrypted JSON backups you control
Secure TOTP Authenticator Export backup dialog comparing Encrypted password-protected JSON export and Plain text export warning
Offline Storage Model

No Cloud Sync—Your Keys Never Leave Your Control

Secure TOTP operates without user accounts, cloud databases, or automatic remote synchronization. Your tokens live strictly inside your local Chrome extension storage—ideal for developers and users working across locked-down corporate networks or internal staging consoles.

Because nothing is mirrored to a vendor server, take two simple habits seriously: export an encrypted password-protected `.json` backup whenever adding important accounts, and retain each website's emergency recovery codes safely offline.

Backup Best Practices →Device Loss Recovery Guide →
Secure TOTP Authenticator Chrome extension icon
Secure TOTP Authenticator · Chrome Extension

Compute Verification Codes Offline Inside Chrome

Zero internet dependency for OTP generation, no registration required, and encrypted JSON backup exports when you need portability.

No signup required Works offline Encrypted local JSON backup
Add to ChromeExplore Secure TOTP Features
Common Questions

Offline Security & Privacy FAQ

Direct answers covering compatibility, security boundaries, offline behavior, and backups.

When you enable 2FA, the website and your authenticator agree on two things once: a shared Base32 secret key (embedded in the QR code) and a 30- or 60-second time step rule. After that moment, both computers independently hash the secret key with the current UTC Unix time window—producing identical codes offline without talking to each other.

Related Secure TOTP Guides & Resources

Explore specialized guides on desktop 2FA, offline TOTP generation, and backup security.

Secure TOTP Product Hub

Extension Workflows & Compatibility

2FA Authenticator for PC

Run an RFC 6238 desktop authenticator inside Chrome on Windows, macOS, or Linux with fast search, one-click copying, and computer security best practices.

Learn more
Chrome Authenticator Extension

Explore QR screenshot scanning, instant search, live 30s/60s countdowns, and objective workflow comparisons between browser and mobile authenticators.

Learn more
TOTP Generator

Deep technical breakdown of SHA-1, SHA-256, and SHA-512 TOTP calculation, 6/8-digit code formatting, 30s/60s time windows, and local execution.

Learn more

Keep Your TOTP Codes Available Offline

Install Secure TOTP Authenticator in Chrome for fast local code generation with zero cloud lock-in.

Add to Chrome — Free