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#include "TOTP.h"
#include "sha1.h"
uint8_t* _hmacKey;
uint8_t _keyLength;
uint8_t _timeZoneOffset;
uint32_t _timeStep;
// Init the library with the private key, its length and the timeStep duration
void TOTP(uint8_t* hmacKey, uint8_t keyLength, uint32_t timeStep) {
_hmacKey = hmacKey;
_keyLength = keyLength;
_timeStep = timeStep;
}
void setTimezone(uint8_t timezone){
_timeZoneOffset = timezone;
}
static uint32_t TimeStruct2Timestamp(struct tm time){
//time.tm_mon -= 1;
//time.tm_year -= 1900;
return mktime(&(time)) - (_timeZoneOffset * 3600) - 2208988800;
}
// Generate a code, using the timestamp provided
uint32_t getCodeFromTimestamp(uint32_t timeStamp) {
uint32_t steps = timeStamp / _timeStep;
return getCodeFromSteps(steps);
}
// Generate a code, using the timestamp provided
uint32_t getCodeFromTimeStruct(struct tm time) {
return getCodeFromTimestamp(TimeStruct2Timestamp(time));
}
// Generate a code, using the number of steps provided
uint32_t getCodeFromSteps(uint32_t steps) {
// STEP 0, map the number of steps in a 8-bytes array (counter value)
uint8_t _byteArray[8];
_byteArray[0] = 0x00;
_byteArray[1] = 0x00;
_byteArray[2] = 0x00;
_byteArray[3] = 0x00;
_byteArray[4] = (uint8_t)((steps >> 24) & 0xFF);
_byteArray[5] = (uint8_t)((steps >> 16) & 0xFF);
_byteArray[6] = (uint8_t)((steps >> 8) & 0XFF);
_byteArray[7] = (uint8_t)((steps & 0XFF));
// STEP 1, get the HMAC-SHA1 hash from counter and key
initHmac(_hmacKey, _keyLength);
writeArray(_byteArray, 8);
uint8_t* _hash = resultHmac();
// STEP 2, apply dynamic truncation to obtain a 4-bytes string
uint32_t _truncatedHash = 0;
uint8_t _offset = _hash[20 - 1] & 0xF;
uint8_t j;
for (j = 0; j < 4; ++j) {
_truncatedHash <<= 8;
_truncatedHash |= _hash[_offset + j];
}
// STEP 3, compute the OTP value
_truncatedHash &= 0x7FFFFFFF; //Disabled
_truncatedHash %= 1000000;
return _truncatedHash;
}
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