.\" Copyright (c) 2018 Yubico AB. All rights reserved.
.\" Use of this source code is governed by a BSD-style
.\" license that can be found in the LICENSE file.
.\"
.Dd $Mdocdate: May 23 2018 $
.Dt FIDO_ASSERT_SET_AUTHDATA 3
.Os
.Sh NAME
.Nm fido_assert_set_authdata ,
.Nm fido_assert_set_authdata_raw ,
.Nm fido_assert_set_clientdata ,
.Nm fido_assert_set_clientdata_hash ,
.Nm fido_assert_set_count ,
.Nm fido_assert_set_extensions ,
.Nm fido_assert_set_hmac_salt ,
.Nm fido_assert_set_hmac_secret ,
.Nm fido_assert_set_up ,
.Nm fido_assert_set_uv ,
.Nm fido_assert_set_rp ,
.Nm fido_assert_set_sig
.Nd set parameters of a FIDO 2 assertion
.Sh SYNOPSIS
.In fido.h
.Bd -literal
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;
.Ed
.Ft int
.Fn fido_assert_set_authdata "fido_assert_t *assert" " size_t idx" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_authdata_raw "fido_assert_t *assert" " size_t idx" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_clientdata "fido_assert_t *assert" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_clientdata_hash "fido_assert_t *assert" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_count "fido_assert_t *assert" "size_t n"
.Ft int
.Fn fido_assert_set_extensions "fido_assert_t *assert" "int flags"
.Ft int
.Fn fido_assert_set_hmac_salt "fido_assert_t *assert" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_hmac_secret "fido_assert_t *assert" "const unsigned char *ptr" "size_t len"
.Ft int
.Fn fido_assert_set_up "fido_assert_t *assert" "fido_opt_t up"
.Ft int
.Fn fido_assert_set_uv "fido_assert_t *assert" "fido_opt_t uv"
.Ft int
.Fn fido_assert_set_rp "fido_assert_t *assert" "const char *id"
.Ft int
.Fn fido_assert_set_sig "fido_assert_t *assert" "size_t idx" "const unsigned char *ptr" "size_t len"
.Sh DESCRIPTION
The
.Nm
set of functions define the various parameters of a FIDO 2
assertion, allowing a
.Fa fido_assert_t
type to be prepared for a subsequent call to
.Xr fido_dev_get_assert 3
or
.Xr fido_assert_verify 3 .
For the complete specification of a FIDO 2 assertion and the format
of its constituent parts, please refer to the Web Authentication
(webauthn) standard.
.Pp
The
.Fn fido_assert_set_count
function sets the number of assertion statements in
.Fa assert
to
.Fa n .
.Pp
The
.Fn fido_assert_set_authdata
and
.Fn fido_assert_set_sig
functions set the authenticator data and signature parts of the
statement with index
.Fa idx
of
.Fa assert
to
.Fa ptr ,
where
.Fa ptr
points to
.Fa len
bytes.
A copy of
.Fa ptr
is made, and no references to the passed pointer are kept.
Please note that the first assertion statement of
.Fa assert
has an
.Fa idx
of
.Em 0 .
The authenticator data passed to
.Fn fido_assert_set_authdata
must be a CBOR-encoded byte string, as obtained from
.Fn fido_assert_authdata_ptr .
Alternatively, a raw binary blob may be passed to
.Fn fido_assert_set_authdata_raw .
.Pp
The
.Fn fido_assert_set_clientdata_hash ,
.Fn fido_assert_set_hmac_salt ,
and
.Fn fido_assert_set_hmac_secret
functions set the client data hash and hmac-salt parts of
.Fa assert
to
.Fa ptr ,
where
.Fa ptr
points to
.Fa len
bytes.
A copy of
.Fa ptr
is made, and no references to the passed pointer are kept.
.Pp
The
.Fn fido_assert_set_clientdata
function allows an application to set the client data hash of
.Fa assert
by specifying the assertion'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
.Fn fido_assert_set_clientdata
instead of
.Fn fido_assert_set_clientdata_hash .
.Pp
The
.Fn fido_assert_set_rp
function sets the relying party
.Fa id
of
.Fa assert ,
where
.Fa id
is a NUL-terminated UTF-8 string.
The content of
.Fa id
is copied, and no references to the passed pointer are kept.
.Pp
The
.Fn fido_assert_set_extensions
function sets the extensions of
.Fa assert
to the bitmask
.Fa flags .
At the moment, only the
.Dv FIDO_EXT_CRED_BLOB ,
.Dv FIDO_EXT_HMAC_SECRET ,
and
.Dv FIDO_EXT_LARGEBLOB_KEY
extensions are supported.
If
.Fa flags
is zero, the extensions of
.Fa assert
are cleared.
.Pp
The
.Fn fido_assert_set_up
and
.Fn fido_assert_set_uv
functions set the
.Fa up
(user presence) and
.Fa uv
(user verification)
attributes of
.Fa assert .
Both are
.Dv FIDO_OPT_OMIT
by default, allowing the authenticator to use its default settings.
.Pp
Use of the
.Nm
set of functions may happen in two distinct situations:
when asking a FIDO device to produce a series of assertion
statements, prior to
.Xr fido_dev_get_assert 3
(i.e, in the context of a FIDO client), or when verifying assertion
statements using
.Xr fido_assert_verify 3
(i.e, in the context of a FIDO server).
.Pp
For a complete description of the generation of a FIDO 2 assertion
and its verification, please refer to the FIDO 2 specification.
An example of how to use the
.Nm
set of functions can be found in the
.Pa examples/assert.c
file shipped with
.Em libfido2 .
.Pp
.Fn fido_assert_set_hmac_secret
is not normally useful in a FIDO client or server \(em it is provided
to enable testing other functionality that relies on retrieving the
HMAC secret from an assertion obtained from an authenticator.
.Sh RETURN VALUES
The
.Nm
functions return
.Dv FIDO_OK
on success.
The error codes returned by the
.Nm
set of functions are defined in
.In fido/err.h .
.Sh SEE ALSO
.Xr fido_assert_allow_cred 3 ,
.Xr fido_assert_verify 3 ,
.Xr fido_dev_get_assert 3