libmutotp

libMUTOTP is a C library designed to bring easy Two-Factor Authentication to MU*s and other text mode applications.

The library can generate TOTP QR codes in ANSI graphics, which you can then display on most ANSI-compatible virtual terminals or MU* clients. The QR codes are smaller than 80x40 characters.

Your users can use any TFA app like "Authenticator", to scan ANSI QR codes and generate one-time passwords with. OTPs can be between 1 and 8 digits long, inclusive (6 is the most popular length).

Usage:

Making a new secret and QR code

char secret[33] = {0};
//Create a base32 encoded secret in an ascii string
generate_random_secret(secret, 33);
printf("Secret: %s\n", secret);

//Create an ANSI QR code graphic. The pointer on the line below owns its new heap memory.
char* qrcodeansi = create_totp_qrcode("Test", "Meow", secret);

printf("--------------------------------------------------------------------------------\n");
printf("%s\n", qrcodeansi);

//Free the memory holding the ANSI QR code graphic
free(qrcodeansi);

Checking the validity of an entered OTP

char secret[33] = {0};
char buf[512] = {0};

//In actual use, you would store the secret with the user's account instead of
//prompting for it, then retrieve it later when he logs in to validate his
//OTPs with.

printf("Enter secret to compute current TOTP:");
scanf("%s", buf);

//Decode the secret from base32 ASCII to its raw data
size_t secretlen = base32decode(buf, strnlen(buf, 512), secret, 33);

//Compute current TOTP using the entered secret and current time.
//The user's authenticator app will do the same calculation for them,
//and if both their app and this program agree (are time-synced and share
//the same secret), the user's OTP will match the one below.
time_t now = time(0);
int otp = compute_totp(secret, secretlen, now, 30, 6);
printf("Current otp code: %06d\n", otp);

Licenses

libmutotp is licensed under the LGPL 2.1. Its SHA1 code was written by Steve Reid and is in public domain. Richard Moore is the author of the qrcode library, which is under the MIT license.