oath_init ()

int
oath_init (void);

This function initializes the OATH library. Every user of this library needs to call this function before using other functions. You should call oath_done() when use of the OATH library is no longer needed.

Note that this function may also initialize Libgcrypt, if the OATH library is built with libgcrypt support and libgcrypt has not been initialized before. Thus if you want to manually initialize libgcrypt you must do it before calling this function. This is useful in cases you want to disable libgcrypt's internal lockings etc.

oath_done ()

int
oath_done (void);

This function deinitializes the OATH library, which were initialized using oath_init(). After calling this function, no other OATH library function may be called except for to re-initialize the library using oath_init().

oath_check_version ()

const char *
oath_check_version (const char *req_version);

Check OATH library version.

See OATH_VERSION for a suitable req_version string.

This function is one of few in the library that can be used without a successful call to oath_init().

oath_strerror ()

const char *
oath_strerror (int err);

Convert return code to human readable string explanation of the reason for the particular error code.

This string can be used to output a diagnostic message to the user.

This function is one of few in the library that can be used without a successful call to oath_init().

Since 1.8.0

oath_strerror_name ()

const char *
oath_strerror_name (int err);

Convert return code to human readable string representing the error code symbol itself. For example, oath_strerror_name(OATH_OK) returns the string "OATH_OK".

This string can be used to output a diagnostic message to the user.

This function is one of few in the library that can be used without a successful call to oath_init().

Since 1.8.0

oath_hex2bin ()

int
oath_hex2bin (const char *hexstr,
              char *binstr,
              size_t *binlen);

Convert string with hex data to binary data.

Non-hexadecimal data are not ignored but instead will lead to an OATH_INVALID_HEX error.

If binstr is NULL, then binlen will be populated with the necessary length. If the binstr buffer is too small, OATH_TOO_SMALL_BUFFER is returned and binlen will contain the necessary length.

oath_bin2hex ()

void
oath_bin2hex (const char *binstr,
              size_t binlen,
              char *hexstr);

Convert binary data to NUL-terminated string with hex data. The output hexstr is allocated by the caller and must have room for at least 2*binlen +1, to make room for the encoded data and the terminating NUL byte.

Since 1.12.0

oath_base32_decode ()

int
oath_base32_decode (const char *in,
                    size_t inlen,
                    char **out,
                    size_t *outlen);

Decode a base32 encoded string into binary data.

Space characters are ignored and pad characters are added if needed. Non-base32 data are not ignored but instead will lead to an OATH_INVALID_BASE32 error.

The in parameter should contain inlen bytes of base32 encoded data. The function allocates a new string in *out to hold the decoded data, and sets *outlen to the length of the data.

If out is NULL, then *outlen will be set to what would have been the length of *out on successful encoding.

If the caller is not interested in knowing the length of the output data out , then outlen may be set to NULL.

It is permitted but useless to have both out and outlen NULL.

Since 1.12.0

oath_base32_encode ()

int
oath_base32_encode (const char *in,
                    size_t inlen,
                    char **out,
                    size_t *outlen);

Encode binary data into a string with base32 data.

The in parameter should contain inlen bytes of data to encode. The function allocates a new string in *out to hold the encoded data, and sets *outlen to the length of the data. The output string *out is zero-terminated (ASCII NUL), but the NUL is not counted in *outlen .

If out is NULL, then *outlen will be set to what would have been the length of *out on successful encoding.

If the caller is not interested in knowing the length of the output data out , then outlen may be set to NULL.

It is permitted but useless to have both out and outlen NULL.

Since 1.12.0

OATH_HOTP_LENGTH()

#define OATH_HOTP_LENGTH(digits, checksum) (digits + (checksum ? 1 : 0))

oath_hotp_generate ()

int
oath_hotp_generate (const char *secret,
                    size_t secret_length,
                    uint64_t moving_factor,
                    unsigned  digits,
                    bool add_checksum,
                    size_t truncation_offset,
                    char *output_otp);

Generate a one-time-password using the HOTP algorithm as described in RFC 4226.

Use a value of OATH_HOTP_DYNAMIC_TRUNCATION for truncation_offset unless you really need a specific truncation offset.

To find out the size of the OTP you may use the OATH_HOTP_LENGTH() macro. The output_otp buffer must be have room for that length plus one for the terminating NUL.

Currently only values 6, 7 and 8 for digits are supported, and the add_checksum value is ignored. These restrictions may be lifted in future versions, although some limitations are inherent in the protocol.

oath_hotp_validate ()

int
oath_hotp_validate (const char *secret,
                    size_t secret_length,
                    uint64_t start_moving_factor,
                    size_t window,
                    const char *otp);

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

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.

oath_validate_strcmp_function ()

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

Prototype of strcmp-like function that will be called by oath_hotp_validate_callback() or oath_totp_validate_callback() to validate OTPs.

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 oath_strcmp hash the test_otp OTP using the same hash, and then compare the results.

Since 1.6.0

oath_hotp_validate_callback ()

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);

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.

Since 1.4.0

oath_totp_generate ()

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

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.

Since 1.4.0

oath_totp_generate2 ()

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);

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.

Since 2.6.0

oath_totp_validate ()

int
oath_totp_validate (const char *secret,
                    size_t secret_length,
                    time_t now,
                    unsigned  time_step_size,
                    time_t start_offset,
                    size_t window,
                    const char *otp);

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

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.

Since 1.6.0

oath_totp_validate_callback ()

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);

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.

Since 1.6.0

oath_totp_validate2 ()

int
oath_totp_validate2 (const char *secret,
                     size_t secret_length,
                     time_t now,
                     unsigned  time_step_size,
                     time_t start_offset,
                     size_t window,
                     int *otp_pos,
                     const char *otp);

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

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.

Since 1.10.0

oath_totp_validate2_callback ()

int
oath_totp_validate2_callback (const char *secret,
                              size_t secret_length,
                              time_t now,
                              unsigned  time_step_size,
                              time_t start_offset,
                              unsigned  digits,
                              size_t window,
                              int *otp_pos,
                              oath_validate_strcmp_function strcmp_otp,
                              void *strcmp_handle);

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.

Since 1.10.0

oath_totp_validate3 ()

int
oath_totp_validate3 (const char *secret,
                     size_t secret_length,
                     time_t now,
                     unsigned  time_step_size,
                     time_t start_offset,
                     size_t window,
                     int *otp_pos,
                     uint64_t *otp_counter,
                     const char *otp);

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

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.

Since 2.4.0

oath_totp_validate3_callback ()

int
oath_totp_validate3_callback (const char *secret,
                              size_t secret_length,
                              time_t now,
                              unsigned  time_step_size,
                              time_t start_offset,
                              unsigned  digits,
                              size_t window,
                              int *otp_pos,
                              uint64_t *otp_counter,
                              oath_validate_strcmp_function strcmp_otp,
                              void *strcmp_handle);

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.

Since 2.4.0

oath_totp_validate4 ()

int
oath_totp_validate4 (const char *secret,
                     size_t secret_length,
                     time_t now,
                     unsigned  time_step_size,
                     time_t start_offset,
                     size_t window,
                     int *otp_pos,
                     uint64_t *otp_counter,
                     int flags,
                     const char *otp);

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

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.

The flags parameter may be used to change the MAC function, for example OATH_TOTP_HMAC_SHA256 or OATH_TOTP_HMAC_SHA512.

Since 2.6.0

oath_totp_validate4_callback ()

int
oath_totp_validate4_callback (const char *secret,
                              size_t secret_length,
                              time_t now,
                              unsigned  time_step_size,
                              time_t start_offset,
                              unsigned  digits,
                              size_t window,
                              int *otp_pos,
                              uint64_t *otp_counter,
                              int flags,
                              oath_validate_strcmp_function strcmp_otp,
                              void *strcmp_handle);

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.

The flags parameter may be used to change the MAC function, for example OATH_TOTP_HMAC_SHA256 or OATH_TOTP_HMAC_SHA512.

Since 2.6.0

oath_authenticate_usersfile ()

int
oath_authenticate_usersfile (const char *usersfile,
                             const char *username,
                             const char *otp,
                             size_t window,
                             const char *passwd,
                             time_t *last_otp);

Authenticate user named username with the one-time password otp and (optional) password passwd . Credentials are read (and updated) from a text file named usersfile .

Note that for TOTP the usersfile will only record the last OTP and use that to make sure more recent OTPs have not been seen yet when validating a new OTP. That logics relies on using the same search window for the same user.

OATHAPI

#  define OATHAPI __attribute__((__visibility__("default")))

OATH_VERSION

#define OATH_VERSION "2.6.2"

Pre-processor symbol with a string that describe the header file version number. Used together with oath_check_version() to verify header file and run-time library consistency.

OATH_VERSION_NUMBER

#define OATH_VERSION_NUMBER 0x02060200

Pre-processor symbol with a hexadecimal value describing the header file version number. For example, when the header version is 1.2.3 this symbol will have the value 0x01020300. The last two digits are only used between public releases, and will otherwise be 00.

enum oath_rc

Return codes for OATH functions. All return codes are negative except for the successful code OATH_OK which are guaranteed to be

Note that the oath_rc enumeration may be extended at a later date to include new return codes.

OATH_HOTP_DYNAMIC_TRUNCATION

#define OATH_HOTP_DYNAMIC_TRUNCATION SIZE_MAX

oath_hotp_validate_strcmp_function

#define oath_hotp_validate_strcmp_function oath_validate_strcmp_function

OATH_TOTP_DEFAULT_TIME_STEP_SIZE

#define OATH_TOTP_DEFAULT_TIME_STEP_SIZE 30

OATH_TOTP_DEFAULT_START_TIME

#define OATH_TOTP_DEFAULT_START_TIME		((time_t) 0)

enum oath_totp_flags

Flags for oath_totp_generate2().

Since 2.6.0