oath_hotp_validate_callback man page

oath_hotp_validate_callback — API function

Synopsis

#include <oath.h>

int oath_hotp_validate_callback(const char * secret, size_t secret_length, uint64_t start_moving_factor, size_t window, unsigned digits, oath_validate_strcmp_function strcmp_otp, void * strcmp_handle);

Arguments

const char * secret
the shared secret string
size_t secret_length
length of secret
uint64_t start_moving_factor
start counter in OTP stream
size_t window
how many OTPs after start counter to test
unsigned digits
number of requested digits in the OTP
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.

Description

Validate an OTP according to OATH HOTP algorithm per RFC 4226.

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

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.

Since

1.4.0

Reporting Bugs

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

Info

2.6.1 liboath liboath