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oath_totp_validate_callback - Man Page

API function


#include <oath.h>

int oath_totp_validate_callback(const char * secret, size_t secret_length, time_t now, unsigned time_step_size, time_t start_offset, unsigned digits, size_t window, oath_validate_strcmp_function strcmp_otp, void * strcmp_handle);


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

size_t window

how many OTPs after start counter to test

oath_validate_strcmp_function strcmp_otp

function pointer to a strcmp-like function.

void * strcmp_handle

caller handle to be passed on to strcmp_otp.


Validate an OTP according to OATH TOTP algorithm per RFC 6238.

Validation is implemented by generating a number of potential OTPs and performing a call to the strcmp_otp function, to compare the potential OTP against the given otp.  It has the following prototype:

int (*oath_validate_strcmp_function) (void *handle, const char *test_otp);

The function should be similar to strcmp in that it return 0 only on matches.  It differs by permitting use of negative return codes as indication of internal failures in the callback.  Positive values indicate OTP mismatch.

This callback interface is useful when you cannot compare OTPs directly using normal strcmp, but instead for example only have a hashed OTP.  You would then typically pass in the hashed OTP in the strcmp_handle and let your implementation of strcmp_otp hash the test_otp OTP using the same hash, and then compare the results.

Currently only OTP lengths of 6, 7 or 8 digits are supported.  This restrictions may be lifted in future versions, although some limitations are inherent in the protocol.


Returns position in OTP window (zero is first position), or OATH_INVALID_OTP if no OTP was found in OTP window, or an error code.



Reporting Bugs

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


2.6.11 liboath