oath_totp_generate2(3)

NAME
oath_totp_generate2 - API function

SYNOPSIS
#include <oath.h>

int oath_totp_generate2(const char * secret, size_t secret_length, time_t now, unsigned time_step_size, time_t start_offset, unsigned digits, int flags, char * output_otp);

ARGUMENTS

const char * secret
    the shared secret string

size_t secret_length
    length of secret

time_t now
    Unix time value to compute TOTP for

unsigned time_step_size
    time step system parameter (typically 30)

time_t start_offset
    Unix time of when to start counting time steps (typically 0)

unsigned digits
    number of requested digits in the OTP, excluding checksum

int flags
    flags indicating mode, one of oath_totp_flags

char * output_otp
    output buffer, must have room for the output OTP plus zero

DESCRIPTION
Generate a one-time-password using the time-variant TOTP algorithm described in RFC 6238. The input parameters are taken as time values. The system parameter time_step_size describes how long the time window for each OTP is. The recommended value is 30 seconds, and you can use the value 0 or the symbol OATH_TOTP_DEFAULT_TIME_STEP_SIZE to indicate this. The system parameter start_offset denote the Unix time when time steps are started to be counted. The recommended value is 0, to fall back on the Unix epoch) and you can use the symbol OATH_TOTP_DEFAULT_START_TIME to indicate this. The output_otp buffer must have room for at least digits characters, plus one for the terminating NUL. Currently only values 6, 7 and 8 for digits are supported. This restriction may be lifted in future versions. The flags parameter may be used to change the MAC function, for example OATH_TOTP_HMAC_SHA256 or OATH_TOTP_HMAC_SHA512.

RETURNS
On success, OATH_OK (zero) is returned, otherwise an error code is returned.

SINCE
2.6.0

REPORTING BUGS
Report bugs to <oath-toolkit-help@nongnu.org>. liboath home page: https://oath-toolkit.codeberg.page/ General help using GNU software: http://www.gnu.org/gethelp/

COPYRIGHT
Copyright © 2009-2026 Simon Josefsson.
Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.