sensor-watch/movement/lib/TOTP/README.md

TOTP Pure C Library

Library to generate Time-based One-Time Passwords.

Implements the Time-based One-Time Password algorithm specified in RFC 6238.

Supports different time steps and is compatible with tokens that use the same standard (including software ones, like the Google Authenticator app).

The code is made of :

• TOTP-MCU for TimeStruct2Timestamp, getCodeFromTimestamp, getCodeFromTimeStruct, part of getCodeFromSteps and TOTP_HMAC_SHA* functions
• mbedtls for SHA1/SHA224/SHA256/SHA384/SHA512 implementations
• this project as an inspiration for writing the code to compute the TOTP using the key and the text to hash

Supported algorithms are SHA1/SHA224/SHA256/SHA384/SHA512.

Installation & usage:

First include header to your file

#include "TOTP.h"

After included, define key ex. Key is MyLegoDoor

• Note: The format of hmacKey is array of hexadecimal bytes.
• Most websites provide the key encoded in base32 - RFC3548/RFC4648, either upper or lower case. You can use this site to convert the base32 string to hex (make sure you upcase it first if it's lowercase and remove all whitespaces).

uint8_t hmacKey[] = {0x4d, 0x79, 0x4c, 0x65, 0x67, 0x6f, 0x44, 0x6f, 0x6f, 0x72};               // Secret key

Instantiate the TOTP class by providing the secret hmacKey, the length of the hmacKey, the Timestep between codes and the algorithm used (most of the time, SHA1).

TOTP(hmacKey, 10, 30, SHA1);                                     // Secret key, Secret key length, Timestep (30s), Algorithm

Use the getCodeFromTimestamp() function to get a TOTP from a unix epoch timestamp

uint32_t newCode = getCodeFromTimestamp(1557414000);       // Current timestamp since Unix epoch in seconds

Or getCodeFromTimeStruct() if you want to get a TOTP from a tm struct (Time Struct in C),

struct tm datetime;
datetime.tm_hour = 9;
datetime.tm_min = 0;
datetime.tm_sec = 0;
datetime.tm_mday = 13;
datetime.tm_mon = 5;
datetime.tm_year = 2019;
uint32_t newCode = getCodeFromTimeStruct(datetime);

If the provided unix timestamp isn't in UTC±0, use setTimezone() before getCodeFromTimestamp() or getCodeFromTimeStruct() to offset the time.

setTimezone(9);                                            // Set timezone +9 Japan

You can see an example in example.c (compile it with gcc -o example example.c sha1.c sha256.c sha512.c TOTP.c -I.)

Thanks to:

• Netthaw, https://github.com/Netthaw/TOTP-MCU
• Mbed-TLS, https://github.com/Mbed-TLS/mbedtls
• mygityf, https://github.com/mygityf/cipher/blob/master/cipher/hmac.c
• susam, https://github.com/susam/mintotp