sjmulder / totp

TOTP generator in C with no dependencies

totp

From-scratch, dependency-free implementation of TOTP, including SHA1, for education. TOTP is the most common standard for generating codes in 'Authenticator' apps.

Live web version: https://sjmulder.nl/totp/

Details

Sources:

• totp.{c,h} - the algorithms.
• std.{c,h} - some libc functions for freestanding targets (WASM, GBA).
• main.c - a simple CLI.
• test.c - unit tests.
• index.html - a frondend for the WASM build.

Targets:

• totp - the CLI.
• totp{32,64}.exe - the CLI, for Windows.
• totp.wasm - a WebAssembly build, used by index.html.

TOTP generators take a seed (the "shared secret"), which is usually presented as a QR code or base32-encoded string when setting up the authenticator.

This implementation generates codes for the current time given a seed, but the CLI nor the WASM web version store seeds for later use.

Building

• make to build CLI using default C compiler.
• make check to run tests.
• make cross to build Windows and WASM targets.

For Windows and WASM, default compilers and flags are specified in the Makefile but can be overridden with make flags or config.mk, which is automatically included if it exists.

Author

Sijmen Mulder ([email protected]). See LICENSE.md.