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provider-keymgmt - The KEYMGMT library <-> provider functions


 #include <openssl/core_dispatch.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.
 /* Key object (keydata) creation and destruction */
 void *OSSL_FUNC_keymgmt_new(void *provctx);
 void OSSL_FUNC_keymgmt_free(void *keydata);
 /* Generation, a more complex constructor */
 void *OSSL_FUNC_keymgmt_gen_init(void *provctx, int selection,
                                  const OSSL_PARAM params[]);
 int OSSL_FUNC_keymgmt_gen_set_template(void *genctx, void *template);
 int OSSL_FUNC_keymgmt_gen_set_params(void *genctx, const OSSL_PARAM params[]);
 const OSSL_PARAM *OSSL_FUNC_keymgmt_gen_settable_params(void *genctx,
                                                         void *provctx);
 void *OSSL_FUNC_keymgmt_gen(void *genctx, OSSL_CALLBACK *cb, void *cbarg);
 void OSSL_FUNC_keymgmt_gen_cleanup(void *genctx);
 /* Key loading by object reference, also a constructor */
 void *OSSL_FUNC_keymgmt_load(const void *reference, size_t *reference_sz);
 /* Key object information */
 int OSSL_FUNC_keymgmt_get_params(void *keydata, OSSL_PARAM params[]);
 const OSSL_PARAM *OSSL_FUNC_keymgmt_gettable_params(void *provctx);
 int OSSL_FUNC_keymgmt_set_params(void *keydata, const OSSL_PARAM params[]);
 const OSSL_PARAM *OSSL_FUNC_keymgmt_settable_params(void *provctx);
 /* Key object content checks */
 int OSSL_FUNC_keymgmt_has(const void *keydata, int selection);
 int OSSL_FUNC_keymgmt_match(const void *keydata1, const void *keydata2,
                             int selection);
 /* Discovery of supported operations */
 const char *OSSL_FUNC_keymgmt_query_operation_name(int operation_id);
 /* Key object import and export functions */
 int OSSL_FUNC_keymgmt_import(void *keydata, int selection, const OSSL_PARAM params[]);
 const OSSL_PARAM *OSSL_FUNC_keymgmt_import_types(int selection);
 int OSSL_FUNC_keymgmt_export(void *keydata, int selection,
                              OSSL_CALLBACK *param_cb, void *cbarg);
 const OSSL_PARAM *OSSL_FUNC_keymgmt_export_types(int selection);
 /* Key object duplication, a constructor */
 void *OSSL_FUNC_keymgmt_dup(const void *keydata_from, int selection);
 /* Key object validation */
 int OSSL_FUNC_keymgmt_validate(const void *keydata, int selection, int checktype);


The KEYMGMT operation doesn't have much public visibility in OpenSSL libraries, it's rather an internal operation that's designed to work in tandem with operations that use private/public key pairs.

Because the KEYMGMT operation shares knowledge with the operations it works with in tandem, they must belong to the same provider. The OpenSSL libraries will ensure that they do.

The primary responsibility of the KEYMGMT operation is to hold the provider side key data for the OpenSSL library EVP_PKEY structure.

All "functions" mentioned here are passed as function pointers between libcrypto and the provider in OSSL_DISPATCH arrays via OSSL_ALGORITHM 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 a OSSL_DISPATCH element named OSSL_FUNC_{name}. For example, the "function" OSSL_FUNC_keymgmt_new() has these:

 typedef void *(OSSL_FUNC_keymgmt_new_fn)(void *provctx);
 static ossl_inline OSSL_FUNC_keymgmt_new_fn
     OSSL_FUNC_keymgmt_new(const OSSL_DISPATCH *opf);

OSSL_DISPATCH arrays are indexed by numbers that are provided as macros in openssl-core_dispatch.h(7), as follows:

 OSSL_FUNC_keymgmt_new                  OSSL_FUNC_KEYMGMT_NEW
 OSSL_FUNC_keymgmt_free                 OSSL_FUNC_KEYMGMT_FREE
 OSSL_FUNC_keymgmt_gen_init             OSSL_FUNC_KEYMGMT_GEN_INIT
 OSSL_FUNC_keymgmt_gen_set_template     OSSL_FUNC_KEYMGMT_GEN_SET_TEMPLATE
 OSSL_FUNC_keymgmt_gen_set_params       OSSL_FUNC_KEYMGMT_GEN_SET_PARAMS
 OSSL_FUNC_keymgmt_gen                  OSSL_FUNC_KEYMGMT_GEN
 OSSL_FUNC_keymgmt_gen_cleanup          OSSL_FUNC_KEYMGMT_GEN_CLEANUP
 OSSL_FUNC_keymgmt_load                 OSSL_FUNC_KEYMGMT_LOAD
 OSSL_FUNC_keymgmt_get_params           OSSL_FUNC_KEYMGMT_GET_PARAMS
 OSSL_FUNC_keymgmt_set_params           OSSL_FUNC_KEYMGMT_SET_PARAMS
 OSSL_FUNC_keymgmt_has                  OSSL_FUNC_KEYMGMT_HAS
 OSSL_FUNC_keymgmt_validate             OSSL_FUNC_KEYMGMT_VALIDATE
 OSSL_FUNC_keymgmt_match                OSSL_FUNC_KEYMGMT_MATCH
 OSSL_FUNC_keymgmt_import               OSSL_FUNC_KEYMGMT_IMPORT
 OSSL_FUNC_keymgmt_import_types         OSSL_FUNC_KEYMGMT_IMPORT_TYPES
 OSSL_FUNC_keymgmt_export               OSSL_FUNC_KEYMGMT_EXPORT
 OSSL_FUNC_keymgmt_export_types         OSSL_FUNC_KEYMGMT_EXPORT_TYPES
 OSSL_FUNC_keymgmt_dup                  OSSL_FUNC_KEYMGMT_DUP

Key Objects

A key object is a collection of data for an asymmetric key, and is represented as keydata in this manual.

The exact contents of a key object are defined by the provider, and it is assumed that different operations in one and the same provider use the exact same structure to represent this collection of data, so that for example, a key object that has been created using the KEYMGMT interface that we document here can be passed as is to other provider operations, such as OP_signature_sign_init() (see provider-signature(7)).

With some of the KEYMGMT functions, it's possible to select a specific subset of data to handle, governed by the bits in a selection indicator. The bits are:

Indicating that the private key data in a key object should be considered.
Indicating that the public key data in a key object should be considered.
Indicating that the domain parameters in a key object should be considered.
Indicating that other parameters in a key object should be considered.

Other parameters are key parameters that don't fit any other classification. In other words, this particular selector bit works as a last resort bit bucket selector.

Some selector bits have also been combined for easier use:

Indicating that all key object parameters should be considered, regardless of their more granular classification.


Indicating that both the whole key pair in a key object should be considered, i.e. the combination of public and private key.


Indicating that everything in a key object should be considered.

The exact interpretation of those bits or how they combine is left to each function where you can specify a selector.

It's left to the provider implementation to decide what is reasonable to do with regards to received selector bits and how to do it. Among others, an implementation of OSSL_FUNC_keymgmt_match() might opt to not compare the private half if it has compared the public half, since a match of one half implies a match of the other half.

Constructing and Destructing Functions

OSSL_FUNC_keymgmt_new() should create a provider side key object. The provider context provctx is passed and may be incorporated in the key object, but that is not mandatory.

OSSL_FUNC_keymgmt_free() should free the passed keydata.

OSSL_FUNC_keymgmt_gen_init(), OSSL_FUNC_keymgmt_gen_set_template(), OSSL_FUNC_keymgmt_gen_set_params(), OSSL_FUNC_keymgmt_gen_settable_params(), OSSL_FUNC_keymgmt_gen() and OSSL_FUNC_keymgmt_gen_cleanup() work together as a more elaborate context based key object constructor.

OSSL_FUNC_keymgmt_gen_init() should create the key object generation context and initialize it with selections, which will determine what kind of contents the key object to be generated should get. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_keymgmt_set_params().

OSSL_FUNC_keymgmt_gen_set_template() should add template to the context genctx. The template is assumed to be a key object constructed with the same KEYMGMT, and from which content that the implementation chooses can be used as a template for the key object to be generated. Typically, the generation of a DSA or DH key would get the domain parameters from this template.

OSSL_FUNC_keymgmt_gen_set_params() should set additional parameters from params in the key object generation context genctx.

OSSL_FUNC_keymgmt_gen_settable_params() should return a constant array of descriptor OSSL_PARAM, for parameters that OSSL_FUNC_keymgmt_gen_set_params() can handle.

OSSL_FUNC_keymgmt_gen() should perform the key object generation itself, and return the result. The callback cb should be called at regular intervals with indications on how the key object generation progresses.

OSSL_FUNC_keymgmt_gen_cleanup() should clean up and free the key object generation context genctx

OSSL_FUNC_keymgmt_load() creates a provider side key object based on a reference object with a size of reference_sz bytes, that only the provider knows how to interpret, but that may come from other operations. Outside the provider, this reference is simply an array of bytes.

At least one of OSSL_FUNC_keymgmt_new(), OSSL_FUNC_keymgmt_gen() and OSSL_FUNC_keymgmt_load() are mandatory, as well as OSSL_FUNC_keymgmt_free() and OSSL_FUNC_keymgmt_has(). Additionally, if OSSL_FUNC_keymgmt_gen() is present, OSSL_FUNC_keymgmt_gen_init() and OSSL_FUNC_keymgmt_gen_cleanup() must be present as well.

Key Object Information Functions

OSSL_FUNC_keymgmt_get_params() should extract information data associated with the given keydata, see "Common Information Parameters".

OSSL_FUNC_keymgmt_gettable_params() should return a constant array of descriptor OSSL_PARAM, for parameters that OSSL_FUNC_keymgmt_get_params() can handle.

If OSSL_FUNC_keymgmt_gettable_params() is present, OSSL_FUNC_keymgmt_get_params() must also be present, and vice versa.

OSSL_FUNC_keymgmt_set_params() should update information data associated with the given keydata, see "Common Information Parameters".

OSSL_FUNC_keymgmt_settable_params() should return a constant array of descriptor OSSL_PARAM, for parameters that OSSL_FUNC_keymgmt_set_params() can handle.

If OSSL_FUNC_keymgmt_settable_params() is present, OSSL_FUNC_keymgmt_set_params() must also be present, and vice versa.

Key Object Checking Functions

OSSL_FUNC_keymgmt_query_operation_name() should return the name of the supported algorithm for the operation operation_id. This is similar to provider_query_operation() (see provider-base(7)), but only works as an advisory. If this function is not present, or returns NULL, the caller is free to assume that there's an algorithm from the same provider, of the same name as the one used to fetch the keymgmt and try to use that.

OSSL_FUNC_keymgmt_has() should check whether the given keydata contains the subsets of data indicated by the selector. A combination of several selector bits must consider all those subsets, not just one. An implementation is, however, free to consider an empty subset of data to still be a valid subset. For algorithms where some selection is not meaningful such as OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS for RSA keys the function should just return 1 as the selected subset is not really missing in the key.

OSSL_FUNC_keymgmt_validate() should check if the keydata contains valid data subsets indicated by selection. Some combined selections of data subsets may cause validation of the combined data. For example, the combination of OSSL_KEYMGMT_SELECT_PRIVATE_KEY and OSSL_KEYMGMT_SELECT_PUBLIC_KEY (or OSSL_KEYMGMT_SELECT_KEYPAIR for short) is expected to check that the pairwise consistency of keydata is valid. The checktype parameter controls what type of check is performed on the subset of data. Two types of check are defined: OSSL_KEYMGMT_VALIDATE_FULL_CHECK and OSSL_KEYMGMT_VALIDATE_QUICK_CHECK. The interpretation of how much checking is performed in a full check versus a quick check is key type specific. Some providers may have no distinction between a full check and a quick check. For algorithms where some selection is not meaningful such as OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS for RSA keys the function should just return 1 as there is nothing to validate for that selection.

OSSL_FUNC_keymgmt_match() should check if the data subset indicated by selection in keydata1 and keydata2 match. It is assumed that the caller has ensured that keydata1 and keydata2 are both owned by the implementation of this function.

Key Object Import, Export and Duplication Functions

OSSL_FUNC_keymgmt_import() should import data indicated by selection into keydata with values taken from the OSSL_PARAM array params.

OSSL_FUNC_keymgmt_export() should extract values indicated by selection from keydata, create an OSSL_PARAM array with them and call param_cb with that array as well as the given cbarg.

OSSL_FUNC_keymgmt_import_types() should return a constant array of descriptor OSSL_PARAM for data indicated by selection, for parameters that OSSL_FUNC_keymgmt_import() can handle.

OSSL_FUNC_keymgmt_export_types() should return a constant array of descriptor OSSL_PARAM for data indicated by selection, that the OSSL_FUNC_keymgmt_export() callback can expect to receive.

OSSL_FUNC_keymgmt_dup() should duplicate data subsets indicated by selection or the whole key data keydata_from and create a new provider side key object with the data.

Common Information Parameters

See OSSL_PARAM(3) for further details on the parameters structure.

Common information parameters currently recognised by all built-in keymgmt algorithms are as follows:

"bits" (OSSL_PKEY_PARAM_BITS) <integer>
The value should be the cryptographic length of the cryptosystem to which the key belongs, in bits. The definition of cryptographic length is specific to the key cryptosystem.
"max-size" (OSSL_PKEY_PARAM_MAX_SIZE) <integer>
The value should be the maximum size that a caller should allocate to safely store a signature (called sig in provider-signature(7)), the result of asymmmetric encryption / decryption (out in provider-asym_cipher(7), a derived secret (secret in provider-keyexch(7), and similar data).

Because an EVP_KEYMGMT method is always tightly bound to another method (signature, asymmetric cipher, key exchange, ...) and must be of the same provider, this number only needs to be synchronised with the dimensions handled in the rest of the same provider.

"security-bits" (OSSL_PKEY_PARAM_SECURITY_BITS) <integer>
The value should be the number of security bits of the given key. Bits of security is defined in SP800-57.


OSSL_FUNC_keymgmt_new() and OSSL_FUNC_keymgmt_dup() should return a valid reference to the newly created provider side key object, or NULL on failure.

OSSL_FUNC_keymgmt_import(), OSSL_FUNC_keymgmt_export(), OSSL_FUNC_keymgmt_get_params() and OSSL_FUNC_keymgmt_set_params() should return 1 for success or 0 on error.

OSSL_FUNC_keymgmt_validate() should return 1 on successful validation, or 0 on failure.

OSSL_FUNC_keymgmt_has() should return 1 if all the selected data subsets are contained in the given keydata or 0 otherwise.

OSSL_FUNC_keymgmt_query_operation_name() should return a pointer to a string matching the requested operation, or NULL if the same name used to fetch the keymgmt applies.

OSSL_FUNC_keymgmt_gettable_params() and OSSL_FUNC_keymgmt_settable_params() OSSL_FUNC_keymgmt_import_types(), OSSL_FUNC_keymgmt_export_types() should always return a constant OSSL_PARAM array.


provider(7), EVP_PKEY-X25519(7), EVP_PKEY-X448(7), EVP_PKEY-ED25519(7), EVP_PKEY-ED448(7), EVP_PKEY-EC(7), EVP_PKEY-RSA(7), EVP_PKEY-DSA(7), EVP_PKEY-DH(7)


The KEYMGMT interface was introduced in OpenSSL 3.0.


Copyright 2019-2022 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 <>.

2022-08-14 3.0.5