EVP_SKEY¶

NAME¶

EVP_SKEY, EVP_SKEY_generate, EVP_SKEY_import, EVP_SKEY_import_raw_key, EVP_SKEY_import_SKEYMGMT, EVP_SKEY_up_ref, EVP_SKEY_export, EVP_SKEY_get0_raw_key, EVP_SKEY_get0_key_id, EVP_SKEY_get0_skeymgmt_name, EVP_SKEY_get0_provider_name, EVP_SKEY_free, EVP_SKEY_is_a, EVP_SKEY_to_provider, EVP_SKEY_get0_local_keyid, EVP_SKEY_get0_algorithm_id - opaque symmetric key allocation and handling functions

SYNOPSIS¶

#include <openssl/evp.h>

typedef evp_skey_st EVP_SKEY;

EVP_SKEY *EVP_SKEY_generate(OSSL_LIB_CTX *libctx, const char *skeymgmtname,
                            const char *propquery, const OSSL_PARAM *params);
EVP_SKEY *EVP_SKEY_import(OSSL_LIB_CTX *libctx, const char *skeymgmtname,
                          const char *propquery,
                          int selection, const OSSL_PARAM *params);
EVP_SKEY *EVP_SKEY_import_raw_key(OSSL_LIB_CTX *libctx, const char *skeymgmtname,
                                  unsigned char *key, size_t len,
                                  const char *propquery);
EVP_SKEY *EVP_SKEY_import_SKEYMGMT(OSSL_LIB_CTX *libctx, EVP_SKEYMGMT *skeymgmt,
                                   int selection, const OSSL_PARAM *params);
int EVP_SKEY_export(const EVP_SKEY *skey, int selection,
                    OSSL_CALLBACK *export_cb, void *export_cbarg);
int EVP_SKEY_get0_raw_key(const EVP_SKEY *skey, const unsigned char **key,
                         size_t *len);
const char *EVP_SKEY_get0_key_id(const EVP_SKEY *skey);

const char *EVP_SKEY_get0_skeymgmt_name(const EVP_SKEY *skey);
const char *EVP_SKEY_get0_provider_name(const EVP_SKEY *skey);

int EVP_SKEY_up_ref(EVP_SKEY *key);
void EVP_SKEY_free(EVP_SKEY *key);
int EVP_SKEY_is_a(const EVP_SKEY *skey, const char *name);
EVP_SKEY *EVP_SKEY_to_provider(EVP_SKEY *skey, OSSL_LIB_CTX *libctx,
                               OSSL_PROVIDER *prov, const char *propquery);

int EVP_SKEY_get0_local_keyid(const EVP_SKEY *skey,
                              const unsigned char **id, size_t *len);
int EVP_SKEY_get0_algorithm_id(const EVP_SKEY *skey,
                                const unsigned char **oid, size_t *oid_len,
                                const unsigned char **params,
                                size_t *params_len);

DESCRIPTION¶

EVP_SKEY is a generic structure to hold symmetric keys as opaque objects. The keys themselves are often referred to as the "internal key", and are handled by providers using EVP_SKEYMGMT(3).

Conceptually, an EVP_SKEY internal key may hold a symmetric key, and along with those, key parameters if the key type requires them.

The EVP_SKEY_generate() functions creates a new EVP_SKEY object and initializes it according to the params argument.

The EVP_SKEY_import() function allocates an empty EVP_SKEY structure which is used by OpenSSL to store symmetric keys, assigns the EVP_SKEYMGMT object associated with the key, and initializes the object from the params argument.

The EVP_SKEY_import_raw_key() function is a helper that creates an EVP_SKEY object containing the raw byte representation of the symmetric keys from the buffer key having length len. The skeymgmtname defines the name of the target EVP_SKEYMGMT for the newly created key.

The EVP_SKEY_import_SKEYMGMT() function is a helper that creates an EVP_SKEY object containing the representation of the symmetric keys specific to the particular EVP_SKEYMGMT.

The EVP_SKEY_export() function extracts values from a key skey using the selection. selection is described below. It uses a callback export_cb that gets passed the value of export_cbarg. See openssl-core.h(7) for more information about the callback. Note that the OSSL_PARAM(3) array that is passed to the callback is not persistent after the callback returns.

The EVP_SKEY_get0_raw_key() returns a pointer to a raw key bytes to the passed address and sets the key len. The returned address is managed by the internal key management and shouldn't be freed explicitly. The operation can fail when the underlying key management doesn't support export of the secret key.

The EVP_SKEY_get0_key_id() returns a NUL-terminated string providing some human-readable identifier of the key if provided by the underlying key management. The pointer becomes invalid after freeing the EVP_SKEY object.

The EVP_SKEY_get0_skeymgmt_name() and EVP_SKEY_get0_provider_name() return the names of the associated EVP_SKEYMGMT object and its provider correspondingly.

EVP_SKEY_up_ref() increments the reference count of key.

EVP_SKEY_free() decrements the reference count of key and, if the reference count is zero, frees it. If key is NULL, nothing is done.

EVP_SKEY_is_a() checks if the key type of skey is name.

EVP_SKEY_to_provider() simplifies the task of importing a skey into a different provider identified by prov. If prov is NULL, the default provider for the key type identified via skey is used.

Metadata¶

An EVP_SKEY object can carry optional metadata alongside the cryptographic key material. This metadata is managed by the provider through the EVP_SKEYMGMT import/export mechanism and stored in the provider-side key data.

The friendly name (alias) is accessible via EVP_SKEY_get0_key_id(), which dispatches to the provider's OSSL_FUNC_skeymgmt_get_key_id function. The built-in providers return the value of OSSL_SKEY_PARAM_ALIAS if it was set during import.

EVP_SKEY_get0_local_keyid() retrieves the local key identifier from skey. On success, *id is set to a pointer to the identifier bytes and *len is set to the length. The returned pointer is valid for the lifetime of skey. Returns 1 on success, 0 on error.

EVP_SKEY_get0_algorithm_id() retrieves the algorithm identifier from skey. It can return both the DER-encoded algorithm OID (via oid and oid_len) and the DER-encoded algorithm parameters (via params and params_len). Either output pair may be NULL if the caller does not need that part. The returned pointers are valid for the lifetime of skey. Returns 1 on success, 0 on error.

These metadata fields are populated on obtaining the key object (e.g. when parsing PKCS#12 files). For PKCS#12 files the friendly name and local key ID correspond to PKCS#12 bag attributes (NID_friendlyName and NID_localKeyID), while the algorithm OID and parameters are extracted from the PKCS8 AlgorithmIdentifier.

The implementation is in general provider-dependent. If the corresponding callback is not implemented for the EVP_SKEYMGMT, 0 is returned. However, as metadata is completely optional, the success doesn't indicate that the data is available.

Selections¶

The following constants can be used for selection:

OSSL_SKEYMGMT_SELECT_SECRET_KEY

Only the raw key representation will be selected.
OSSL_SKEYMGMT_SELECT_PARAMETERS

Only the key parameters will be selected. This includes optional key parameters.
OSSL_SKEYMGMT_SELECT_ALL

All parameters will be selected.

NOTES¶

The EVP_SKEY structure is used by various OpenSSL functions which require a general symmetric key without reference to any particular algorithm.

The EVP_SKEY_to_provider() function will fail and return NULL if the origin key skey cannot be exported from its provider.

RETURN VALUES¶

EVP_SKEY_generate(), EVP_SKEY_import(), EVP_SKEY_import_raw_key(), and EVP_SKEY_import_SKEYMGMT() return either the newly allocated EVP_SKEY structure or NULL if an error occurred.

EVP_SKEY_get0_key_id() returns either a valid pointer or NULL.

EVP_SKEY_up_ref() returns 1 for success and 0 on failure.

EVP_SKEY_export() and EVP_SKEY_get0_raw_key() return 1 for success and 0 on failure.

EVP_SKEY_get0_skeymgmt_name() and EVP_SKEY_get0_provider_name() return the names of the associated EVP_SKEYMGMT object and its provider correspondingly.

EVP_SKEY_is_a() returns 1 if skey has the key type name, otherwise 0.

EVP_SKEY_to_provider() returns a new EVP_SKEY suitable for operations with the prov provider or NULL in case of failure.

EVP_SKEY_get0_local_keyid() and EVP_SKEY_get0_algorithm_id() return 1 on success or 0 on error.

HISTORY¶

The EVP_SKEY API and functions EVP_SKEY_export(), EVP_SKEY_free(), EVP_SKEY_get0_raw_key(), EVP_SKEY_import(), EVP_SKEY_import_raw_key(), EVP_SKEY_up_ref(), EVP_SKEY_generate(), EVP_SKEY_get0_key_id(), EVP_SKEY_get0_provider_name(), EVP_SKEY_get0_skeymgmt_name(), EVP_SKEY_is_a(), EVP_SKEY_to_provider() were introduced in OpenSSL 3.5.

The EVP_SKEY_import_SKEYMGMT() function was introduced in OpenSSL 4.0.

The EVP_SKEY_get0_local_keyid() and EVP_SKEY_get0_algorithm_id() functions were added in OpenSSL 4.1.

COPYRIGHT¶

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.