FIDO_CRED_NEW(3) | Library Functions Manual | FIDO_CRED_NEW(3)

# NAME

`fido_cred_new`, `fido_cred_free`, `fido_cred_pin_minlen`, `fido_cred_prot`, `fido_cred_fmt`, `fido_cred_rp_id`, `fido_cred_rp_name`, `fido_cred_user_name`, `fido_cred_display_name`, `fido_cred_authdata_ptr`, `fido_cred_authdata_raw_ptr`, `fido_cred_clientdata_hash_ptr`, `fido_cred_id_ptr`, `fido_cred_aaguid_ptr`, `fido_cred_largeblob_key_ptr`, `fido_cred_pubkey_ptr`, `fido_cred_sig_ptr`, `fido_cred_user_id_ptr`, `fido_cred_x5c_ptr`, `fido_cred_attstmt_ptr`, `fido_cred_authdata_len`, `fido_cred_authdata_raw_len`, `fido_cred_clientdata_hash_len`, `fido_cred_id_len`, `fido_cred_aaguid_len`, `fido_cred_largeblob_key_len`, `fido_cred_pubkey_len`, `fido_cred_sig_len`, `fido_cred_user_id_len`, `fido_cred_x5c_len`, `fido_cred_attstmt_len`, `fido_cred_type`, `fido_cred_flags`, `fido_cred_sigcount` — FIDO2 credential API

# SYNOPSIS

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

fido_cred_t *
`fido_cred_new`(void);

void
`fido_cred_free`(fido_cred_t **cred_p);

size_t
`fido_cred_pin_minlen`(const fido_cred_t *cred);

int
`fido_cred_prot`(const fido_cred_t *cred);

const char *
`fido_cred_fmt`(const fido_cred_t *cred);

const char *
`fido_cred_rp_id`(const fido_cred_t *cred);

const char *
`fido_cred_rp_name`(const fido_cred_t *cred);

const char *
`fido_cred_user_name`(const fido_cred_t *cred);

const char *
`fido_cred_display_name`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_authdata_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_authdata_raw_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_clientdata_hash_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_id_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_aaguid_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_largeblob_key_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_pubkey_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_sig_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_user_id_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_x5c_ptr`(const fido_cred_t *cred);

const unsigned char *
`fido_cred_attstmt_ptr`(const fido_cred_t *cred);

size_t
`fido_cred_authdata_len`(const fido_cred_t *cred);

size_t
`fido_cred_authdata_raw_len`(const fido_cred_t *cred);

size_t
`fido_cred_clientdata_hash_len`(const fido_cred_t *cred);

size_t
`fido_cred_id_len`(const fido_cred_t *cred);

size_t
`fido_cred_aaguid_len`(const fido_cred_t *cred);

size_t
`fido_cred_largeblob_key_len`(const fido_cred_t *cred);

size_t
`fido_cred_pubkey_len`(const fido_cred_t *cred);

size_t
`fido_cred_sig_len`(const fido_cred_t *cred);

size_t
`fido_cred_user_id_len`(const fido_cred_t *cred);

size_t
`fido_cred_x5c_len`(const fido_cred_t *cred);

size_t
`fido_cred_attstmt_len`(const fido_cred_t *cred);

int
`fido_cred_type`(const fido_cred_t *cred);

uint8_t
`fido_cred_flags`(const fido_cred_t *cred);

uint32_t
`fido_cred_sigcount`(const fido_cred_t *cred);

# DESCRIPTION

FIDO2 credentials are abstracted in libfido2 by the fido_cred_t type. The functions described in this page allow a fido_cred_t type to be allocated, deallocated, and inspected. For other operations on fido_cred_t, please refer to fido_cred_set_authdata(3), fido_cred_exclude(3), fido_cred_verify(3), and fido_dev_make_cred(3).

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

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

If the CTAP 2.1 `FIDO_EXT_MINPINLEN` extension is enabled on cred, then the `fido_cred_pin_minlen`() function returns the minimum PIN length of cred. Otherwise, `fido_cred_pin_minlen`() returns zero. See fido_cred_set_pin_minlen(3) on how to enable this extension.

If the CTAP 2.1 `FIDO_EXT_CRED_PROTECT` extension is enabled on cred, then the `fido_cred_prot`() function returns the protection of cred. Otherwise, `fido_cred_prot`() returns zero. See fido_cred_set_prot(3) for the protection policies understood by libfido2.

The `fido_cred_fmt`() function returns a pointer to a NUL-terminated string containing the format of cred, or NULL if cred does not have a format set.

The `fido_cred_rp_id`(), `fido_cred_rp_name`(), `fido_cred_user_name`(), and `fido_cred_display_name`() functions return pointers to NUL-terminated strings holding the relying party ID, relying party name, user name, and user display name attributes of cred, or NULL if the respective entry is not set.

The `fido_cred_authdata_ptr`(), `fido_cred_authdata_raw_ptr`(), `fido_cred_clientdata_hash_ptr`(), `fido_cred_id_ptr`(), `fido_cred_aaguid_ptr`(), `fido_cred_largeblob_key_ptr`(), `fido_cred_pubkey_ptr`(), `fido_cred_sig_ptr`(), `fido_cred_user_id_ptr`(), `fido_cred_x5c_ptr`(), and `fido_cred_attstmt_ptr`() functions return pointers to the CBOR-encoded and raw authenticator data, client data hash, ID, authenticator attestation GUID, “largeBlobKey”, public key, signature, user ID, x509 certificate, and attestation statement parts of cred, or NULL if the respective entry is not set.

The corresponding length can be obtained by `fido_cred_authdata_len`(), `fido_cred_authdata_raw_len`(), `fido_cred_clientdata_hash_len`(), `fido_cred_id_len`(), `fido_cred_aaguid_len`(), `fido_cred_largeblob_key_len`(), `fido_cred_pubkey_len`(), `fido_cred_sig_len`(), `fido_cred_user_id_len`(), `fido_cred_x5c_len`(), and `fido_cred_attstmt_len`().

The authenticator data, x509 certificate, and signature parts of a credential are typically passed to a FIDO2 server for verification.

The `fido_cred_type`() function returns the COSE algorithm of cred.

The `fido_cred_flags`() function returns the authenticator data flags of cred.

The `fido_cred_sigcount`() function returns the authenticator data signature counter of cred.

# RETURN VALUES

The authenticator data returned by `fido_cred_authdata_ptr`() is a CBOR-encoded byte string, as obtained from the authenticator. To obtain the decoded byte string, use `fido_cred_authdata_raw_ptr`().

If not NULL, pointers returned by `fido_cred_fmt`(), `fido_cred_authdata_ptr`(), `fido_cred_clientdata_hash_ptr`(), `fido_cred_id_ptr`(), `fido_cred_aaguid_ptr`(), `fido_cred_largeblob_key_ptr`(), `fido_cred_pubkey_ptr`(), `fido_cred_sig_ptr`(), and `fido_cred_x5c_ptr`() are guaranteed to exist until any API function that takes cred without the const qualifier is invoked.

# SEE ALSO

fido_cred_exclude(3), fido_cred_set_authdata(3), fido_cred_set_pin_minlen(3), fido_cred_set_prot(3), fido_cred_verify(3), fido_credman_metadata_new(3), fido_dev_largeblob_get(3), fido_dev_make_cred(3)

July 9, 2025 | Debian