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_id, fido_cred_set_clientdata, fido_cred_set_clientdata_hash, fido_cred_set_rp, fido_cred_set_user, fido_cred_set_extensions, fido_cred_set_blob, 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_id(fido_cred_t *cred, const unsigned char *ptr, size_t len);
int
fido_cred_set_clientdata(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_blob(fido_cred_t *cred, const unsigned char *ptr, size_t len);
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(), fido_cred_set_id(), and fido_cred_set_clientdata_hash() functions set the authenticator data, attestation certificate, signature, id, 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().

An application calling fido_cred_set_authdata() does not need to call fido_cred_set_id(). The latter is meant to be used in contexts where the credential's authenticator data is not available.

The fido_cred_set_clientdata() function allows an application to set the client data hash of cred by specifying the credential's unhashed client data. This is required by Windows Hello, which calculates the client data hash internally. For compatibility with Windows Hello, applications should use fido_cred_set_clientdata() instead of fido_cred_set_clientdata_hash().

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_CRED_BLOB, FIDO_EXT_CRED_PROTECT, FIDO_EXT_HMAC_SECRET, and FIDO_EXT_LARGEBLOB_KEY extensions are supported. If flags is zero, the extensions of cred are cleared.

The fido_cred_set_blob() function sets the “credBlob” to be stored with cred to the data pointed to by ptr, which must be len bytes long.

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/discoverable 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 attestation format of cred to fmt, where fmt must be packed (the format used in FIDO2), fido-u2f (the format used by U2F), or none. 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)