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.Dd $Mdocdate: July 15 2022 $
.Dt ES256_PK_NEW 3
.Os
.Sh NAME
.Nm es256_pk_new ,
.Nm es256_pk_free ,
.Nm es256_pk_from_EC_KEY ,
.Nm es256_pk_from_EVP_PKEY ,
.Nm es256_pk_from_ptr ,
.Nm es256_pk_to_EVP_PKEY
.Nd FIDO2 COSE ES256 API
.Sh SYNOPSIS
.In openssl/ec.h
.In fido/es256.h
.Ft es256_pk_t *
.Fn es256_pk_new "void"
.Ft void
.Fn es256_pk_free "es256_pk_t **pkp"
.Ft int
.Fn es256_pk_from_EC_KEY "es256_pk_t *pk" "const EC_KEY *ec"
.Ft int
.Fn es256_pk_from_EVP_PKEY "es256_pk_t *pk" "const EVP_PKEY *pkey"
.Ft int
.Fn es256_pk_from_ptr "es256_pk_t *pk" "const void *ptr" "size_t len"
.Ft EVP_PKEY *
.Fn es256_pk_to_EVP_PKEY "const es256_pk_t *pk"
.Sh DESCRIPTION
ES256 is the name given in the CBOR Object Signing and Encryption
(COSE) RFC to ECDSA over P-256 with SHA-256.
The COSE ES256 API of
.Em libfido2
is an auxiliary API with routines to convert between the different
ECDSA public key types used in
.Em libfido2
and
.Em OpenSSL .
.Pp
In
.Em libfido2 ,
ES256 public keys are abstracted by the
.Vt es256_pk_t
type.
.Pp
The
.Fn es256_pk_new
function returns a pointer to a newly allocated, empty
.Vt es256_pk_t
type.
If memory cannot be allocated, NULL is returned.
.Pp
The
.Fn es256_pk_free
function releases the memory backing
.Fa *pkp ,
where
.Fa *pkp
must have been previously allocated by
.Fn es256_pk_new .
On return,
.Fa *pkp
is set to NULL.
Either
.Fa pkp
or
.Fa *pkp
may be NULL, in which case
.Fn es256_pk_free
is a NOP.
.Pp
The
.Fn es256_pk_from_EC_KEY
function fills
.Fa pk
with the contents of
.Fa ec .
No references to
.Fa ec
are kept.
.Pp
The
.Fn es256_pk_from_EVP_PKEY
function fills
.Fa pk
with the contents of
.Fa pkey .
No references to
.Fa pkey
are kept.
.Pp
The
.Fn es256_pk_from_ptr
function fills
.Fa pk
with the contents of
.Fa ptr ,
where
.Fa ptr
points to
.Fa len
bytes.
The
.Fa ptr
pointer may point to an uncompressed point, or to the
concatenation of the x and y coordinates.
No references to
.Fa ptr
are kept.
.Pp
The
.Fn es256_pk_to_EVP_PKEY
function converts
.Fa pk
to a newly allocated
.Fa EVP_PKEY
type with a reference count of 1.
No internal references to the returned pointer are kept.
If an error occurs,
.Fn es256_pk_to_EVP_PKEY
returns NULL.
.Sh RETURN VALUES
The
.Fn es256_pk_from_EC_KEY ,
.Fn es256_pk_from_EVP_PKEY ,
and
.Fn es256_pk_from_ptr
functions return
.Dv FIDO_OK
on success.
On error, a different error code defined in
.In fido/err.h
is returned.
.Sh SEE ALSO
.Xr eddsa_pk_new 3 ,
.Xr es384_pk_new 3 ,
.Xr fido_assert_verify 3 ,
.Xr fido_cred_pubkey_ptr 3 ,
.Xr rs256_pk_new 3