| PROVIDER-KDF(7SSL) | OpenSSL | PROVIDER-KDF(7SSL) |
provider-kdf - The KDF library <-> provider functions
#include <openssl/core_dispatch.h>
#include <openssl/core_names.h>
/*
* None of these are actual functions, but are displayed like this for
* the function signatures for functions that are offered as function
* pointers in OSSL_DISPATCH arrays.
*/
/* Context management */
void *OSSL_FUNC_kdf_newctx(void *provctx);
void OSSL_FUNC_kdf_freectx(void *kctx);
void *OSSL_FUNC_kdf_dupctx(void *src);
/* Encryption/decryption */
int OSSL_FUNC_kdf_reset(void *kctx);
int OSSL_FUNC_kdf_derive(void *kctx, unsigned char *key, size_t keylen,
const OSSL_PARAM params[]);
/* KDF parameter descriptors */
const OSSL_PARAM *OSSL_FUNC_kdf_gettable_params(void *provctx);
const OSSL_PARAM *OSSL_FUNC_kdf_gettable_ctx_params(void *kcxt, void *provctx);
const OSSL_PARAM *OSSL_FUNC_kdf_settable_ctx_params(void *kcxt, void *provctx);
/* KDF parameters */
int OSSL_FUNC_kdf_get_params(OSSL_PARAM params[]);
int OSSL_FUNC_kdf_get_ctx_params(void *kctx, OSSL_PARAM params[]);
int OSSL_FUNC_kdf_set_ctx_params(void *kctx, const OSSL_PARAM params[]);
This documentation is primarily aimed at provider authors. See provider(7) for further information.
The KDF operation enables providers to implement KDF algorithms and make them available to applications via the API functions EVP_KDF_CTX_reset(3), and EVP_KDF_derive(3).
All "functions" mentioned here are passed as function pointers between libcrypto and the provider in OSSL_DISPATCH(3) arrays via OSSL_ALGORITHM(3) arrays that are returned by the provider's provider_query_operation() function (see "Provider Functions" in provider-base(7)).
All these "functions" have a corresponding function type definition named OSSL_FUNC_{name}_fn, and a helper function to retrieve the function pointer from an OSSL_DISPATCH(3) element named OSSL_FUNC_{name}. For example, the "function" OSSL_FUNC_kdf_newctx() has these:
typedef void *(OSSL_FUNC_kdf_newctx_fn)(void *provctx);
static ossl_inline OSSL_FUNC_kdf_newctx_fn
OSSL_FUNC_kdf_newctx(const OSSL_DISPATCH *opf);
OSSL_DISPATCH(3) array entries are identified by numbers that are provided as macros in openssl-core_dispatch.h(7), as follows:
OSSL_FUNC_kdf_newctx OSSL_FUNC_KDF_NEWCTX OSSL_FUNC_kdf_freectx OSSL_FUNC_KDF_FREECTX OSSL_FUNC_kdf_dupctx OSSL_FUNC_KDF_DUPCTX OSSL_FUNC_kdf_reset OSSL_FUNC_KDF_RESET OSSL_FUNC_kdf_derive OSSL_FUNC_KDF_DERIVE OSSL_FUNC_kdf_get_params OSSL_FUNC_KDF_GET_PARAMS OSSL_FUNC_kdf_get_ctx_params OSSL_FUNC_KDF_GET_CTX_PARAMS OSSL_FUNC_kdf_set_ctx_params OSSL_FUNC_KDF_SET_CTX_PARAMS OSSL_FUNC_kdf_gettable_params OSSL_FUNC_KDF_GETTABLE_PARAMS OSSL_FUNC_kdf_gettable_ctx_params OSSL_FUNC_KDF_GETTABLE_CTX_PARAMS OSSL_FUNC_kdf_settable_ctx_params OSSL_FUNC_KDF_SETTABLE_CTX_PARAMS
A KDF algorithm implementation may not implement all of these functions. In order to be a consistent set of functions, at least the following functions must be implemented: OSSL_FUNC_kdf_newctx(), OSSL_FUNC_kdf_freectx(), OSSL_FUNC_kdf_set_ctx_params(), OSSL_FUNC_kdf_derive(). All other functions are optional.
OSSL_FUNC_kdf_newctx() should create and return a pointer to a provider side structure for holding context information during a KDF operation. A pointer to this context will be passed back in a number of the other KDF operation function calls. The parameter provctx is the provider context generated during provider initialisation (see provider(7)).
OSSL_FUNC_kdf_freectx() is passed a pointer to the provider side KDF context in the kctx parameter. If it receives NULL as kctx value, it should not do anything other than return. This function should free any resources associated with that context.
OSSL_FUNC_kdf_dupctx() should duplicate the provider side KDF context in the kctx parameter and return the duplicate copy.
OSSL_FUNC_kdf_reset() initialises a KDF operation given a provider side KDF context in the kctx parameter.
OSSL_FUNC_kdf_derive() performs the KDF operation after processing the params as per OSSL_FUNC_kdf_set_ctx_params(). The kctx parameter contains a pointer to the provider side context. The resulting key of the desired keylen should be written to key. If the algorithm does not support the requested keylen the function must return error.
See OSSL_PARAM(3) for further details on the parameters structure used by these functions.
OSSL_FUNC_kdf_get_params() gets details of parameter values associated with the provider algorithm and stores them in params.
OSSL_FUNC_kdf_set_ctx_params() sets KDF parameters associated with the given provider side KDF context kctx to params. Any parameter settings are additional to any that were previously set. Passing NULL for params should return true.
OSSL_FUNC_kdf_get_ctx_params() retrieves gettable parameter values associated with the given provider side KDF context kctx and stores them in params. Passing NULL for params should return true.
OSSL_FUNC_kdf_gettable_params(), OSSL_FUNC_kdf_gettable_ctx_params(), and OSSL_FUNC_kdf_settable_ctx_params() all return constant OSSL_PARAM(3) arrays as descriptors of the parameters that OSSL_FUNC_kdf_get_params(), OSSL_FUNC_kdf_get_ctx_params(), and OSSL_FUNC_kdf_set_ctx_params() can handle, respectively. OSSL_FUNC_kdf_gettable_ctx_params() and OSSL_FUNC_kdf_settable_ctx_params() will return the parameters associated with the provider side context kctx in its current state if it is not NULL. Otherwise, they return the parameters associated with the provider side algorithm provctx.
Parameters currently recognised by built-in KDFs are as follows. Not all parameters are relevant to, or are understood by all KDFs:
The checks performed are:
OSSL_FUNC_kdf_newctx() and OSSL_FUNC_kdf_dupctx() should return the newly created provider side KDF context, or NULL on failure.
OSSL_FUNC_kdf_derive(), OSSL_FUNC_kdf_get_params(), OSSL_FUNC_kdf_get_ctx_params() and OSSL_FUNC_kdf_set_ctx_params() should return 1 for success or 0 on error.
OSSL_FUNC_kdf_gettable_params(), OSSL_FUNC_kdf_gettable_ctx_params() and OSSL_FUNC_kdf_settable_ctx_params() should return a constant OSSL_PARAM(3) array, or NULL if none is offered.
The KDF life-cycle is described in life_cycle-kdf(7). Providers should ensure that the various transitions listed there are supported. At some point the EVP layer will begin enforcing the listed transitions.
The provider KDF interface was introduced in OpenSSL 3.0.
Copyright 2020-2023 The OpenSSL Project Authors. All Rights Reserved.
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>.
| 2023-10-23 | 3.0.11 |