NAME

       provider-keyexch - The keyexch library <-> provider functions

SYNOPSIS

        #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_keyexch_newctx(void *provctx);
        void OSSL_FUNC_keyexch_freectx(void *ctx);
        void *OSSL_FUNC_keyexch_dupctx(void *ctx);

        /* Shared secret derivation */
        int OSSL_FUNC_keyexch_init(void *ctx, void *provkey,
                                   const OSSL_PARAM params[]);
        int OSSL_FUNC_keyexch_set_peer(void *ctx, void *provkey);
        int OSSL_FUNC_keyexch_derive(void *ctx, unsigned char *secret, size_t *secretlen,
                                     size_t outlen);

        /* Key Exchange parameters */
        int OSSL_FUNC_keyexch_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
        const OSSL_PARAM *OSSL_FUNC_keyexch_settable_ctx_params(void *ctx,
                                                                void *provctx);
        int OSSL_FUNC_keyexch_get_ctx_params(void *ctx, OSSL_PARAM params[]);
        const OSSL_PARAM *OSSL_FUNC_keyexch_gettable_ctx_params(void *ctx,
                                                                void *provctx);

DESCRIPTION

       This documentation is primarily aimed at provider authors. See provider(7) for further
       information.

       The key exchange (OSSL_OP_KEYEXCH) operation enables providers to implement key exchange
       algorithms and make them available to applications via EVP_PKEY_derive(3) and other
       related functions).

       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 an
       OSSL_DISPATCH element named OSSL_FUNC_{name}.  For example, the "function"
       OSSL_FUNC_keyexch_newctx() has these:

        typedef void *(OSSL_FUNC_keyexch_newctx_fn)(void *provctx);
        static ossl_inline OSSL_FUNC_keyexch_newctx_fn
            OSSL_FUNC_keyexch_newctx(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_keyexch_newctx                OSSL_FUNC_KEYEXCH_NEWCTX
        OSSL_FUNC_keyexch_freectx               OSSL_FUNC_KEYEXCH_FREECTX
        OSSL_FUNC_keyexch_dupctx                OSSL_FUNC_KEYEXCH_DUPCTX

        OSSL_FUNC_keyexch_init                  OSSL_FUNC_KEYEXCH_INIT
        OSSL_FUNC_keyexch_set_peer              OSSL_FUNC_KEYEXCH_SET_PEER
        OSSL_FUNC_keyexch_derive                OSSL_FUNC_KEYEXCH_DERIVE

        OSSL_FUNC_keyexch_set_ctx_params        OSSL_FUNC_KEYEXCH_SET_CTX_PARAMS
        OSSL_FUNC_keyexch_settable_ctx_params   OSSL_FUNC_KEYEXCH_SETTABLE_CTX_PARAMS
        OSSL_FUNC_keyexch_get_ctx_params        OSSL_FUNC_KEYEXCH_GET_CTX_PARAMS
        OSSL_FUNC_keyexch_gettable_ctx_params   OSSL_FUNC_KEYEXCH_GETTABLE_CTX_PARAMS

       A key exchange algorithm implementation may not implement all of these functions.  In
       order to be a consistent set of functions a provider must implement
       OSSL_FUNC_keyexch_newctx, OSSL_FUNC_keyexch_freectx, OSSL_FUNC_keyexch_init and
       OSSL_FUNC_keyexch_derive.  All other functions are optional.

       A key exchange algorithm must also implement some mechanism for generating, loading or
       importing keys via the key management (OSSL_OP_KEYMGMT) operation.  See
       provider-keymgmt(7) for further details.

   Context Management Functions
       OSSL_FUNC_keyexch_newctx() should create and return a pointer to a provider side structure
       for holding context information during a key exchange operation.  A pointer to this
       context will be passed back in a number of the other key exchange operation function
       calls.  The parameter provctx is the provider context generated during provider
       initialisation (see provider(7)).

       OSSL_FUNC_keyexch_freectx() is passed a pointer to the provider side key exchange context
       in the ctx parameter.  This function should free any resources associated with that
       context.

       OSSL_FUNC_keyexch_dupctx() should duplicate the provider side key exchange context in the
       ctx parameter and return the duplicate copy.

   Shared Secret Derivation Functions
       OSSL_FUNC_keyexch_init() initialises a key exchange operation given a provider side key
       exchange context in the ctx parameter, and a pointer to a provider key object in the
       provkey parameter.  The params, if not NULL, should be set on the context in a manner
       similar to using OSSL_FUNC_keyexch_set_params().  The key object should have been
       previously generated, loaded or imported into the provider using the key management
       (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)>.

       OSSL_FUNC_keyexch_set_peer() is called to supply the peer's public key (in the provkey
       parameter) to be used when deriving the shared secret.  It is also passed a previously
       initialised key exchange context in the ctx parameter.  The key object should have been
       previously generated, loaded or imported into the provider using the key management
       (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)>.

       OSSL_FUNC_keyexch_derive() performs the actual key exchange itself by deriving a shared
       secret.  A previously initialised key exchange context is passed in the ctx parameter.
       The derived secret should be written to the location secret which should not exceed outlen
       bytes.  The length of the shared secret should be written to *secretlen.  If secret is
       NULL then the maximum length of the shared secret should be written to *secretlen.

   Key Exchange Parameters Functions
       OSSL_FUNC_keyexch_set_ctx_params() sets key exchange parameters associated with the given
       provider side key exchange context ctx to params, see "Common Key Exchange parameters".
       Any parameter settings are additional to any that were previously set.  Passing NULL for
       params should return true.

       OSSL_FUNC_keyexch_get_ctx_params() gets key exchange parameters associated with the given
       provider side key exchange context ctx into params, see "Common Key Exchange parameters".
       Passing NULL for params should return true.

       OSSL_FUNC_keyexch_settable_ctx_params() yields a constant OSSL_PARAM array that describes
       the settable parameters, i.e. parameters that can be used with
       OP_signature_set_ctx_params().  If OSSL_FUNC_keyexch_settable_ctx_params() is present,
       OSSL_FUNC_keyexch_set_ctx_params() must also be present, and vice versa.  Similarly,
       OSSL_FUNC_keyexch_gettable_ctx_params() yields a constant OSSL_PARAM array that describes
       the gettable parameters, i.e. parameters that can be handled by
       OP_signature_get_ctx_params().  If OSSL_FUNC_keyexch_gettable_ctx_params() is present,
       OSSL_FUNC_keyexch_get_ctx_params() must also be present, and vice versa.  See
       OSSL_PARAM(3) for the use of OSSL_PARAM as parameter descriptor.

       Notice that not all settable parameters are also gettable, and vice versa.

   Common Key Exchange parameters
       See OSSL_PARAM(3) for further details on the parameters structure used by the
       OSSL_FUNC_keyexch_set_ctx_params() and OSSL_FUNC_keyexch_get_ctx_params() functions.

       Common parameters currently recognised by built-in key exchange algorithms are as follows.

       "kdf-type" (OSSL_EXCHANGE_PARAM_KDF_TYPE) <UTF8 string>
           Sets or gets the Key Derivation Function type to apply within the associated key
           exchange ctx.

       "kdf-digest" (OSSL_EXCHANGE_PARAM_KDF_DIGEST) <UTF8 string>
           Sets or gets the Digest algorithm to be used as part of the Key Derivation Function
           associated with the given key exchange ctx.

       "kdf-digest-props" (OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS) <UTF8 string>
           Sets properties to be used upon look up of the implementation for the selected Digest
           algorithm for the Key Derivation Function associated with the given key exchange ctx.

       "kdf-outlen" (OSSL_EXCHANGE_PARAM_KDF_OUTLEN) <unsigned integer>
           Sets or gets the desired size for the output of the chosen Key Derivation Function
           associated with the given key exchange ctx.  The length of the "kdf-outlen" parameter
           should not exceed that of a size_t.

       "kdf-ukm" (OSSL_EXCHANGE_PARAM_KDF_UKM) <octet string>
           Sets the User Key Material to be used as part of the selected Key Derivation Function
           associated with the given key exchange ctx.

       "kdf-ukm" (OSSL_EXCHANGE_PARAM_KDF_UKM) <octet string ptr>
           Gets a pointer to the User Key Material to be used as part of the selected Key
           Derivation Function associated with the given key exchange ctx. Providers usually do
           not need to support this gettable parameter as its sole purpose is to support
           functionality of the deprecated EVP_PKEY_CTX_get0_ecdh_kdf_ukm() and
           EVP_PKEY_CTX_get0_dh_kdf_ukm() functions.

RETURN VALUES

       OSSL_FUNC_keyexch_newctx() and OSSL_FUNC_keyexch_dupctx() should return the newly created
       provider side key exchange context, or NULL on failure.

       OSSL_FUNC_keyexch_init(), OSSL_FUNC_keyexch_set_peer(), OSSL_FUNC_keyexch_derive(),
       OSSL_FUNC_keyexch_set_params(), and OSSL_FUNC_keyexch_get_params() should return 1 for
       success or 0 on error.

       OSSL_FUNC_keyexch_settable_ctx_params() and OSSL_FUNC_keyexch_gettable_ctx_params() should
       always return a constant OSSL_PARAM array.

SEE ALSO

       provider(7)

HISTORY

       The provider KEYEXCH interface was introduced in OpenSSL 3.0.

COPYRIGHT

       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 <https://www.openssl.org/source/license.html>.