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oath_hotp_validate_callback(3)      liboath     oath_hotp_validate_callback(3)


NAME

       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/


COPYRIGHT

       Copyright (C) 2009-2015 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.

liboath                              2.6.1      oath_hotp_validate_callback(3)

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