YET ANOTHER SIMPLE TOTP TOKEN GENERATOR IN PURE C

This is a simple (re)implementation of the TOTP Token generator written in Pure C and following the references:

• RFC6238
• RFC4226

It doesn't expose any external api, you can just build it and use with the most popular provider that implement the RFC specification.

BUILD FROM SRC

You can simply build it using the provided Makefile. When you run make it generates a ./usr/bin/c_otp within the project root dir with the result of the compilation. Before building, make sure the dependencies are installed.

For example:

$ podman run --rm --name c_otp -it quay.io/fedora/fedora:latest /bin/bash
$ dnf install -y make git gcc openssl-devel
$ git clone https://github.com/fmount/c_otp
$ pushd c_otp
$ make

Run the example:

$ ./usr/bin/c_otp -f providerrc
[(google: 418346)(amazon: 071288)(protonmail: 418346)]

USAGE

$ ./c_otp -h
Usage ./bin/c_otp [-f fname] | [-b b32_secretkey] [-m mode] [-v]

There are two available modes:

• direct: it is used to run a totp calculation on the fly.

$ c_otp -b <BASE32_SECRET>

If the secret is a valid base32, it is first decoded and the computation is performed. To build a simple test vector, you can generate a key example with the following:

$ echo "test" | base32 (ORSXG5A=)

• provider: it is possible to define a provider list in a providerrc file that can be passed as input:

$ ./usr/bin/c_otp -f providerrc -s

The -s flag is used to print on stdout the array containing all the defined providers. As the helper suggests, it is also possible to pass -m <mode> option that can be used to provide a json like format output, useful to interact with other kind of applications, or filter the output using tools like jq.

For example, running the program with -m 1 produces a json output:

$ ./usr/bin/c_otp -f providerrc -m 1

{
    "providers": {
        "protonmail": "123456",
        "google": "123456",
        "amazon": "123456",
    }
}

$ ./c_otp -f providerrc -m 1 | jq '.providers.protonmail'