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.

You can simply build it using the Makefile provided. When you run make it generates a bin/ folder inside the root dir of the project containing the result of the compilation.

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

According to the help of the command, you can have to mode:

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

To do this simply run:

$ c_otp -b <BASE32_SECRET>

and if the secret is a valid base32, it executes the decode and then performs the calculation. If you want to make a test you can generate an example test VECTOR obtained as the following:

$ echo "test" | base32 (ORSXG5A=)

• provider: this is the most interesting mode because you can define the list of your providers in a providerrc file and pass it to the binary:

  $ c_otp -f providerrc -s

The -s flag inspiration is taken from the slstatus suckless project and it is used to print on the STDOUT the array containing all the defined providers. However, as the helper suggests, we can pass the -m mode option which can be used to provide a json like format output, useful to interact with other kind of applications. The accepted values are 0 and 1, where 0 represents the default value if this option is not passed; if 1 is passed as value, a json like format output is provided.

For instance running:

$ ./c_otp -f providerrc -m 1

we can obtain the following output:

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

and it can be parsed using tools like jq; in fact, we can filter by provider name and get just the value running:

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

In the project tree a providerrc.sample is provided and it's used for testing purposes:

#provider:secret ###THIS IS A COMMENT: it will be ignored ..
protonmail:ORSXG5A=
amazon:MVUGY3Y=
google:ORSXG5A=
#trello:ORSKGGGH5A=

You can just use it as a starting point example.