FIDO_CRED_SET_AUTHDATA(3)

FIDO_CRED_SET_AUTHDATA(3) | Library Functions Manual | FIDO_CRED_SET_AUTHDATA(3)

# NAME

`fido_cred_set_authdata`, `fido_cred_set_authdata_raw`, `fido_cred_set_x509`, `fido_cred_set_sig`, `fido_cred_set_clientdata_hash`, `fido_cred_set_rp`, `fido_cred_set_user`, `fido_cred_set_extensions`, `fido_cred_set_prot`, `fido_cred_set_rk`, `fido_cred_set_uv`, `fido_cred_set_fmt`, `fido_cred_set_type` —
set parameters of a FIDO 2 credential

# SYNOPSIS

`#include <fido.h>`

    typedef enum {
    	FIDO_OPT_OMIT = 0, /* use authenticator's default */
    	FIDO_OPT_FALSE,    /* explicitly set option to false */
            FIDO_OPT_TRUE,     /* explicitly set option to true */
    } fido_opt_t;

int
`fido_cred_set_authdata`(fido_cred_t *cred, const unsigned char *ptr, size_t len);

int
`fido_cred_set_authdata_raw`(fido_cred_t *cred, const unsigned char *ptr, size_t len);

int
`fido_cred_set_x509`(fido_cred_t *cred, const unsigned char *ptr, size_t len);

int
`fido_cred_set_sig`(fido_cred_t *cred, const unsigned char *ptr, size_t len);

int
`fido_cred_set_clientdata_hash`(fido_cred_t *cred, const unsigned char *ptr, size_t len);

int
`fido_cred_set_rp`(fido_cred_t *cred, const char *id, const char *name);

int
`fido_cred_set_user`(fido_cred_t *cred, const unsigned char *user_id, size_t user_id_len, const char *name, const char *display_name, const char *icon);

int
`fido_cred_set_extensions`(fido_cred_t *cred, int flags);

int
`fido_cred_set_prot`(fido_cred_t *cred, int prot);

int
`fido_cred_set_rk`(fido_cred_t *cred, fido_opt_t rk);

int
`fido_cred_set_uv`(fido_cred_t *cred, fido_opt_t uv);

int
`fido_cred_set_fmt`(fido_cred_t *cred, const char *ptr);

int
`fido_cred_set_type`(fido_cred_t *cred, int cose_alg);

# DESCRIPTION

The `fido_cred_set_authdata` set of functions define the various parameters of a FIDO 2 credential, allowing a fido_cred_t type to be prepared for a subsequent call to fido_dev_make_cred(3) or fido_cred_verify(3). For the complete specification of a FIDO 2 credential and the format of its constituent parts, please refer to the Web Authentication (webauthn) standard.

The `fido_cred_set_authdata`(), `fido_cred_set_x509`(), `fido_cred_set_sig`(), and `fido_cred_set_clientdata_hash`() functions set the authenticator data, attestation certificate, signature and client data hash parts of cred to ptr, where ptr points to len bytes. A copy of ptr is made, and no references to the passed pointer are kept. The authenticator data passed to `fido_cred_set_authdata`() must be a CBOR-encoded byte string, as obtained from `fido_cred_authdata_ptr`(). Alternatively, a raw binary blob may be passed to `fido_cred_set_authdata_raw`().

The `fido_cred_set_rp`() function sets the relying party id and name parameters of cred, where id and name are NUL-terminated UTF-8 strings. The contents of id and name are copied, and no references to the passed pointers are kept.

The `fido_cred_set_user`() function sets the user attributes of cred, where user_id points to user_id_len bytes and name, display_name, and icon are NUL-terminated UTF-8 strings. The contents of user_id, name, display_name, and icon are copied, and no references to the passed pointers are kept. Previously set user attributes are flushed. The user_id, name, display_name, and icon parameters may be NULL.

The `fido_cred_set_extensions`() function sets the extensions of cred to the bitmask flags. At the moment, only the `FIDO_EXT_HMAC_SECRET` and `FIDO_EXT_CRED_PROTECT` extensions are supported. If flags is zero, the extensions of cred are cleared.

The `fido_cred_set_prot`() function sets the protection of cred to the scalar prot. At the moment, only the `FIDO_CRED_PROT_UV_OPTIONAL`, `FIDO_CRED_PROT_UV_OPTIONAL_WITH_ID`, and `FIDO_CRED_PROT_UV_REQUIRED` protections are supported. If prot is zero, the protection of cred is cleared.

The `fido_cred_set_rk`() and `fido_cred_set_uv`() functions set the rk (resident key) and uv (user verification) attributes of cred. Both are `FIDO_OPT_OMIT` by default, allowing the authenticator to use its default settings.

The `fido_cred_set_fmt`() function sets the format of cred to fmt, where fmt must be either packed (the format used in FIDO 2) or fido-u2f (the format used by U2F). A copy of fmt is made, and no references to the passed pointer are kept. Note that not all authenticators support FIDO2 and therefore may not be able to generate packed.

The `fido_cred_set_type`() function sets the type of cred to cose_alg, where cose_alg is `COSE_ES256`, `COSE_RS256`, or `COSE_EDDSA`. The type of a credential may only be set once. Note that not all authenticators support COSE_RS256 or COSE_EDDSA.

Use of the `fido_cred_set_authdata` set of functions may happen in two distinct situations: when generating a new credential on a FIDO device, prior to fido_dev_make_cred(3) (i.e, in the context of a FIDO client), or when validating a generated credential using fido_cred_verify(3) (i.e, in the context of a FIDO server).

For a complete description of the generation of a FIDO 2 credential and its verification, please refer to the FIDO 2 specification. A concrete utilisation example of the `fido_cred_set_authdata` set of functions can be found in the cred.c example shipped with libfido2.

# RETURN VALUES

The error codes returned by the `fido_cred_set_authdata` set of functions are defined in `<fido/err.h>`. On success, `FIDO_OK` is returned.

# SEE ALSO

fido_cred_exclude(3), fido_cred_verify(3), fido_dev_make_cred(3)

May 23, 2018 | Yubico AB