ES256_PK_NEW(3)

ES256_PK_NEW(3) | Library Functions Manual | ES256_PK_NEW(3)

# NAME

`es256_pk_new`, `es256_pk_free`, `es256_pk_from_EC_KEY`, `es256_pk_from_ptr`, `es256_pk_to_EVP_PKEY` —
FIDO 2 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_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_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`() 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), fido_assert_verify(3), fido_cred_pubkey_ptr(3), rs256_pk_new(3)

May 24, 2018 | Yubico AB