RS256_PK_NEW(3) | Library Functions Manual | RS256_PK_NEW(3)

# NAME

`rs256_pk_new`, `rs256_pk_free`, `rs256_pk_from_RSA`, `rs256_pk_from_EVP_PKEY`, `rs256_pk_from_ptr`, `rs256_pk_to_EVP_PKEY` — FIDO2 COSE RS256 API

# SYNOPSIS

library “libfido2” libcbor libcrypto libz
`#include <openssl/rsa.h>`
`#include <fido/rs256.h>`

rs256_pk_t *
`rs256_pk_new`(void);

void
`rs256_pk_free`(rs256_pk_t **pkp);

int
`rs256_pk_from_EVP_PKEY`(rs256_pk_t *pk, const EVP_PKEY *pkey);

int
`rs256_pk_from_RSA`(rs256_pk_t *pk, const RSA *rsa);

int
`rs256_pk_from_ptr`(rs256_pk_t *pk, const void *ptr, size_t len);

EVP_PKEY *
`rs256_pk_to_EVP_PKEY`(const rs256_pk_t *pk);

# DESCRIPTION

RS256 is the name given in the CBOR Object Signing and Encryption (COSE) RFC to PKCS#1.5 2048-bit RSA with SHA-256. The COSE RS256 API of libfido2 is an auxiliary API with routines to convert between the different RSA public key types used in libfido2 and OpenSSL.

In libfido2, RS256 public keys are abstracted by the rs256_pk_t type.

The `rs256_pk_new`() function returns a pointer to a newly allocated, empty rs256_pk_t type. If memory cannot be allocated, NULL is returned.

The `rs256_pk_free`() function releases the memory backing *pkp, where *pkp must have been previously allocated by `rs256_pk_new`(). On return, *pkp is set to NULL. Either pkp or *pkp may be NULL, in which case `rs256_pk_free`() is a NOP.

The `rs256_pk_from_EVP_PKEY`() function fills pk with the contents of pkey. No references to pkey are kept.

The `rs256_pk_from_RSA`() function fills pk with the contents of rsa. No references to rsa are kept.

The `rs256_pk_from_ptr`() function fills pk with the contents of ptr, where ptr points to len bytes. No references to ptr are kept.

The `rs256_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, `rs256_pk_to_EVP_PKEY`() returns NULL.

# RETURN VALUES

The `rs256_pk_from_EVP_PKEY`(), `rs256_pk_from_RSA`(), and `rs256_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), es256_pk_new(3), fido_assert_verify(3), fido_cred_pubkey_ptr(3)

July 9, 2025 | Debian