NAME

       EVP_KEYEXCH_fetch, EVP_KEYEXCH_free, EVP_KEYEXCH_up_ref, EVP_KEYEXCH_get0_provider, EVP_KEYEXCH_is_a,
       EVP_KEYEXCH_do_all_provided, EVP_KEYEXCH_names_do_all, EVP_KEYEXCH_get0_name,
       EVP_KEYEXCH_get0_description, EVP_KEYEXCH_gettable_ctx_params, EVP_KEYEXCH_settable_ctx_params -
       Functions to manage EVP_KEYEXCH algorithm objects

SYNOPSIS

        #include <openssl/evp.h>

        EVP_KEYEXCH *EVP_KEYEXCH_fetch(OSSL_LIB_CTX *ctx, const char *algorithm,
                                       const char *properties);
        void EVP_KEYEXCH_free(EVP_KEYEXCH *exchange);
        int EVP_KEYEXCH_up_ref(EVP_KEYEXCH *exchange);
        OSSL_PROVIDER *EVP_KEYEXCH_get0_provider(const EVP_KEYEXCH *exchange);
        int EVP_KEYEXCH_is_a(const EVP_KEYEXCH *exchange, const char *name);
        const char *EVP_KEYEXCH_get0_name(const EVP_KEYEXCH *exchange);
        void EVP_KEYEXCH_do_all_provided(OSSL_LIB_CTX *libctx,
                                         void (*fn)(EVP_KEYEXCH *exchange, void *arg),
                                         void *arg);
        int EVP_KEYEXCH_names_do_all(const EVP_KEYEXCH *exchange,
                                     void (*fn)(const char *name, void *data),
                                     void *data);
        const char *EVP_KEYEXCH_get0_description(const EVP_KEYEXCH *keyexch);
        const OSSL_PARAM *EVP_KEYEXCH_gettable_ctx_params(const EVP_KEYEXCH *keyexch);
        const OSSL_PARAM *EVP_KEYEXCH_settable_ctx_params(const EVP_KEYEXCH *keyexch);

DESCRIPTION

       EVP_KEYEXCH_fetch() fetches the key exchange implementation for the given algorithm from any provider
       offering it, within the criteria given by the properties.  See "ALGORITHM FETCHING" in crypto(7) for
       further information.

       The returned value must eventually be freed with EVP_KEYEXCH_free().

       EVP_KEYEXCH_free() decrements the reference count for the EVP_KEYEXCH structure. Typically this structure
       will have been obtained from an earlier call to EVP_KEYEXCH_fetch(). If the reference count drops to 0
       then the structure is freed.

       EVP_KEYEXCH_up_ref() increments the reference count for an EVP_KEYEXCH structure.

       EVP_KEYEXCH_get0_provider() returns the provider that exchange was fetched from.

       EVP_KEYEXCH_is_a() checks if exchange is an implementation of an algorithm that's identifiable with name.

       EVP_KEYEXCH_get0_name() returns the algorithm name from the provided implementation for the given
       exchange. Note that the exchange may have multiple synonyms associated with it. In this case the first
       name from the algorithm definition is returned. Ownership of the returned string is retained by the
       exchange object and should not be freed by the caller.

       EVP_KEYEXCH_names_do_all() traverses all names for the exchange, and calls fn with each name and data.

       EVP_KEYEXCH_get0_description() returns a description of the keyexch, meant for display and human
       consumption.  The description is at the discretion of the keyexch implementation.

       EVP_KEYEXCH_do_all_provided() traverses all key exchange implementations by all activated providers in
       the library context libctx, and for each of the implementations, calls fn with the implementation method
       and data as arguments.

       EVP_KEYEXCH_gettable_ctx_params() and EVP_KEYEXCH_settable_ctx_params() return a constant OSSL_PARAM(3)
       array that describes the names and types of key parameters that can be retrieved or set by a key exchange
       algorithm using EVP_PKEY_CTX_get_params(3) and EVP_PKEY_CTX_set_params(3).

RETURN VALUES

       EVP_KEYEXCH_fetch() returns a pointer to a EVP_KEYEXCH for success or NULL for failure.

       EVP_KEYEXCH_up_ref() returns 1 for success or 0 otherwise.

       EVP_KEYEXCH_names_do_all() returns 1 if the callback was called for all names. A return value of 0 means
       that the callback was not called for any names.

       EVP_KEYEXCH_is_a() returns 1 of exchange was identifiable, otherwise 0.

       EVP_KEYEXCH_gettable_ctx_params() and EVP_KEYEXCH_settable_ctx_params() return a constant OSSL_PARAM(3)
       array or NULL on error.

SEE ALSO

       "ALGORITHM FETCHING" in crypto(7), OSSL_PROVIDER(3)

HISTORY

       The functions described here were added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2019-2021 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>.