NAME

     es256_pk_new, es256_pk_free, es256_pk_from_EC_KEY, es256_pk_from_EVP_PKEY,
     es256_pk_from_ptr, es256_pk_to_EVP_PKEY — FIDO2 COSE ES256 API

SYNOPSIS

     #include <openssl/ec.h>
     #include <fido/es256.h>

     es256_pk_t *
     es256_pk_new(void);

     void
     es256_pk_free(es256_pk_t **pkp);

     int
     es256_pk_from_EC_KEY(es256_pk_t *pk, const EC_KEY *ec);

     int
     es256_pk_from_EVP_PKEY(es256_pk_t *pk, const EVP_PKEY *pkey);

     int
     es256_pk_from_ptr(es256_pk_t *pk, const void *ptr, size_t len);

     EVP_PKEY *
     es256_pk_to_EVP_PKEY(const es256_pk_t *pk);

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 libfido2 is an auxiliary API with routines to
     convert between the different ECDSA public key types used in libfido2 and OpenSSL.

     In libfido2, ES256 public keys are abstracted by the es256_pk_t type.

     The es256_pk_new() function returns a pointer to a newly allocated, empty es256_pk_t type.
     If memory cannot be allocated, NULL is returned.

     The es256_pk_free() function releases the memory backing *pkp, where *pkp must have been
     previously allocated by es256_pk_new().  On return, *pkp is set to NULL.  Either pkp or *pkp
     may be NULL, in which case es256_pk_free() is a NOP.

     The es256_pk_from_EC_KEY() function fills pk with the contents of ec.  No references to ec
     are kept.

     The es256_pk_from_EVP_PKEY() function fills pk with the contents of pkey.  No references to
     pkey are kept.

     The es256_pk_from_ptr() function fills pk with the contents of ptr, where ptr points to len
     bytes.  The ptr pointer may point to an uncompressed point, or to the concatenation of the x
     and y coordinates.  No references to ptr are kept.

     The es256_pk_to_EVP_PKEY() function converts pk to a newly allocated EVP_PKEY type with a
     reference count of 1.  No internal references to the returned pointer are kept.  If an error
     occurs, es256_pk_to_EVP_PKEY() returns NULL.

RETURN VALUES

     The es256_pk_from_EC_KEY(), es256_pk_from_EVP_PKEY(), and es256_pk_from_ptr() functions
     return FIDO_OK on success.  On error, a different error code defined in <fido/err.h> is
     returned.

SEE ALSO

     eddsa_pk_new(3), es384_pk_new(3), fido_assert_verify(3), fido_cred_pubkey_ptr(3),
     rs256_pk_new(3)