FIDO_DEV_OPEN(3) | Library Functions Manual | FIDO_DEV_OPEN(3)

# NAME

`fido_dev_open`, `fido_dev_open_with_info`, `fido_dev_close`, `fido_dev_cancel`, `fido_dev_new`, `fido_dev_new_with_info`, `fido_dev_free`, `fido_dev_force_fido2`, `fido_dev_force_u2f`, `fido_dev_is_fido2`, `fido_dev_is_winhello`, `fido_dev_supports_credman`, `fido_dev_supports_cred_prot`, `fido_dev_supports_permissions`, `fido_dev_supports_pin`, `fido_dev_supports_uv`, `fido_dev_has_pin`, `fido_dev_has_uv`, `fido_dev_protocol`, `fido_dev_build`, `fido_dev_flags`, `fido_dev_major`, `fido_dev_minor` — FIDO2 device open/close and related functions

# SYNOPSIS

library “libfido2” libcbor libcrypto libz
`#include <fido.h>`

int
`fido_dev_open`(fido_dev_t *dev, const char *path);

int
`fido_dev_open_with_info`(fido_dev_t *dev);

int
`fido_dev_close`(fido_dev_t *dev);

int
`fido_dev_cancel`(fido_dev_t *dev);

fido_dev_t *
`fido_dev_new`(void);

fido_dev_t *
`fido_dev_new_with_info`(const fido_dev_info_t *);

void
`fido_dev_free`(fido_dev_t **dev_p);

void
`fido_dev_force_fido2`(fido_dev_t *dev);

void
`fido_dev_force_u2f`(fido_dev_t *dev);

bool
`fido_dev_is_fido2`(const fido_dev_t *dev);

bool
`fido_dev_is_winhello`(const fido_dev_t *dev);

bool
`fido_dev_supports_credman`(const fido_dev_t *dev);

bool
`fido_dev_supports_cred_prot`(const fido_dev_t *dev);

bool
`fido_dev_supports_permissions`(const fido_dev_t *dev);

bool
`fido_dev_supports_pin`(const fido_dev_t *dev);

bool
`fido_dev_supports_uv`(const fido_dev_t *dev);

bool
`fido_dev_has_pin`(const fido_dev_t *dev);

bool
`fido_dev_has_uv`(const fido_dev_t *dev);

uint8_t
`fido_dev_protocol`(const fido_dev_t *dev);

uint8_t
`fido_dev_build`(const fido_dev_t *dev);

uint8_t
`fido_dev_flags`(const fido_dev_t *dev);

uint8_t
`fido_dev_major`(const fido_dev_t *dev);

uint8_t
`fido_dev_minor`(const fido_dev_t *dev);

# DESCRIPTION

The `fido_dev_open`() function opens the device pointed to by path, where dev is a freshly allocated or otherwise closed fido_dev_t. If dev claims to be FIDO2, libfido2 will attempt to speak FIDO2 to dev. If that fails, libfido2 will fallback to U2F unless the `FIDO_DISABLE_U2F_FALLBACK` flag was set in fido_init(3).

The `fido_dev_open_with_info`() function opens dev as previously allocated using `fido_dev_new_with_info`().

The `fido_dev_close`() function closes the device represented by dev. If dev is already closed, `fido_dev_close`() is a NOP.

The `fido_dev_cancel`() function cancels any pending requests on dev.

The `fido_dev_new`() function returns a pointer to a newly allocated, empty fido_dev_t. If memory cannot be allocated, NULL is returned.

The `fido_dev_new_with_info`() function returns a pointer to a newly allocated fido_dev_t with fido_dev_info_t parameters, for use with fido_dev_info_manifest(3) and `fido_dev_open_with_info`(). If memory cannot be allocated, NULL is returned.

The `fido_dev_free`() function releases the memory backing *dev_p, where *dev_p must have been previously allocated by `fido_dev_new`(). On return, *dev_p is set to NULL. Either dev_p or *dev_p may be NULL, in which case `fido_dev_free`() is a NOP.

The `fido_dev_force_fido2`() function can be used to force CTAP2 communication with dev, where dev is an open device.

The `fido_dev_force_u2f`() function can be used to force CTAP1 (U2F) communication with dev, where dev is an open device.

The `fido_dev_is_fido2`() function returns `true` if dev is a FIDO2 device.

The `fido_dev_is_winhello`() function returns `true` if dev is a Windows Hello device.

The `fido_dev_supports_credman`() function returns `true` if dev supports CTAP 2.1 Credential Management.

The `fido_dev_supports_cred_prot`() function returns `true` if dev supports CTAP 2.1 Credential Protection.

The `fido_dev_supports_permissions`() function returns `true` if dev supports CTAP 2.1 UV token permissions.

The `fido_dev_supports_pin`() function returns `true` if dev supports CTAP 2.0 Client PINs.

The `fido_dev_supports_uv`() function returns `true` if dev supports a built-in user verification method.

The `fido_dev_has_pin`() function returns `true` if dev has a CTAP 2.0 Client PIN set.

The `fido_dev_has_uv`() function returns `true` if dev supports built-in user verification and its user verification feature is configured.

The `fido_dev_protocol`() function returns the CTAPHID protocol version identifier of dev.

The `fido_dev_build`() function returns the CTAPHID build version number of dev.

The `fido_dev_flags`() function returns the CTAPHID capabilities flags of dev.

The `fido_dev_major`() function returns the CTAPHID major version number of dev.

The `fido_dev_minor`() function returns the CTAPHID minor version number of dev.

For the format and meaning of the CTAPHID parameters returned by functions above, please refer to the FIDO Client to Authenticator Protocol (CTAP) specification.

# RETURN VALUES

On success, `fido_dev_open`(), `fido_dev_open_with_info`(), and `fido_dev_close`() return `FIDO_OK`. On error, a different error code defined in `<fido/err.h>` is returned.

# SEE ALSO

fido_dev_info_manifest(3), fido_dev_set_io_functions(3), fido_init(3)

July 9, 2025 | Debian