1oath_totp_validate_callback(3)      liboath     oath_totp_validate_callback(3)
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NAME

6       oath_totp_validate_callback - API function
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SYNOPSIS

9       #include <oath.h>
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11       int    oath_totp_validate_callback(const    char   *   secret,   size_t
12       secret_length, time_t now, unsigned time_step_size,  time_t  start_off‐
13       set, unsigned digits, size_t window, oath_validate_strcmp_function str‐
14       cmp_otp, void * strcmp_handle);
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ARGUMENTS

17       const char * secret
18                   the shared secret string
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20       size_t secret_length
21                   length of secret
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23       time_t now  Unix time value to compute TOTP for
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25       unsigned time_step_size
26                   time step system parameter (typically 30)
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28       time_t start_offset
29                   Unix time of when to start counting time  steps  (typically
30                   0)
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32       unsigned digits
33                   number of requested digits in the OTP
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35       size_t window
36                   how many OTPs after start counter to test
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38       oath_validate_strcmp_function strcmp_otp
39                   function pointer to a strcmp-like function.
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41       void * strcmp_handle
42                   caller handle to be passed on to strcmp_otp.
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DESCRIPTION

45       Validate an OTP according to OATH TOTP algorithm per RFC 6238.
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47       Validation  is implemented by generating a number of potential OTPs and
48       performing a call to the strcmp_otp function, to compare the  potential
49       OTP against the given otp.  It has the following prototype:
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51       int   (*oath_validate_strcmp_function)   (void   *handle,   const  char
52       *test_otp);
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54       The function should be similar to strcmp in that it return  0  only  on
55       matches.   It  differs  by  permitting  use of negative return codes as
56       indication of internal failures in the callback.  Positive values indi‐
57       cate OTP mismatch.
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59       This callback interface is useful when you cannot compare OTPs directly
60       using normal strcmp, but instead for example only have  a  hashed  OTP.
61       You  would  then  typically pass in the hashed OTP in the strcmp_handle
62       and let your implementation of strcmp_otp hash the test_otp  OTP  using
63       the same hash, and then compare the results.
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65       Currently  only  OTP  lengths  of 6, 7 or 8 digits are supported.  This
66       restrictions may be lifted in future versions,  although  some  limita‐
67       tions are inherent in the protocol.
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RETURNS

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

74       1.6.0
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REPORTING BUGS

77       Report bugs  to  <oath-toolkit-help@nongnu.org>.   liboath  home  page:
78       http://www.gnu.org/software/liboath/  General  help using GNU software:
79       http://www.gnu.org/gethelp/
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82       Copyright © 2009-2020 Simon Josefsson.
83       Copying and distribution of this file, with  or  without  modification,
84       are  permitted  in  any  medium  without royalty provided the copyright
85       notice and this notice are preserved.
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89liboath                              2.6.6      oath_totp_validate_callback(3)
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