mirror of https://github.com/openssl/openssl.git
260 lines
10 KiB
Plaintext
260 lines
10 KiB
Plaintext
=pod
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=head1 NAME
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provider-keyexch - The keyexch library E<lt>-E<gt> provider functions
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=head1 SYNOPSIS
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=for openssl multiple includes
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#include <openssl/core_numbers.h>
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#include <openssl/core_names.h>
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/*
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* None of these are actual functions, but are displayed like this for
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* the function signatures for functions that are offered as function
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* pointers in OSSL_DISPATCH arrays.
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*/
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/* Context management */
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void *OP_keyexch_newctx(void *provctx);
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void OP_keyexch_freectx(void *ctx);
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void *OP_keyexch_dupctx(void *ctx);
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/* Shared secret derivation */
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int OP_keyexch_init(void *ctx, void *provkey);
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int OP_keyexch_set_peer(void *ctx, void *provkey);
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int OP_keyexch_derive(void *ctx, unsigned char *secret, size_t *secretlen,
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size_t outlen);
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/* Key Exchange parameters */
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int OP_keyexch_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
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const OSSL_PARAM *OP_keyexch_settable_ctx_params(void);
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int OP_keyexch_get_ctx_params(void *ctx, OSSL_PARAM params[]);
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const OSSL_PARAM *OP_keyexch_gettable_ctx_params(void);
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=head1 DESCRIPTION
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This documentation is primarily aimed at provider authors. See L<provider(7)>
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for further information.
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The key exchange (OSSL_OP_KEYEXCH) operation enables providers to implement key
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exchange algorithms and make them available to applications via
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L<EVP_PKEY_derive(3)> and
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other related functions).
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All "functions" mentioned here are passed as function pointers between
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F<libcrypto> and the provider in B<OSSL_DISPATCH> arrays via
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B<OSSL_ALGORITHM> arrays that are returned by the provider's
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provider_query_operation() function
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(see L<provider-base(7)/Provider Functions>).
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All these "functions" have a corresponding function type definition
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named B<OSSL_{name}_fn>, and a helper function to retrieve the
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function pointer from an B<OSSL_DISPATCH> element named
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B<OSSL_get_{name}>.
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For example, the "function" OP_keyexch_newctx() has these:
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typedef void *(OSSL_OP_keyexch_newctx_fn)(void *provctx);
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static ossl_inline OSSL_OP_keyexch_newctx_fn
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OSSL_get_OP_keyexch_newctx(const OSSL_DISPATCH *opf);
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B<OSSL_DISPATCH> arrays are indexed by numbers that are provided as
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macros in L<openssl-core_numbers.h(7)>, as follows:
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OP_keyexch_newctx OSSL_FUNC_KEYEXCH_NEWCTX
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OP_keyexch_freectx OSSL_FUNC_KEYEXCH_FREECTX
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OP_keyexch_dupctx OSSL_FUNC_KEYEXCH_DUPCTX
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OP_keyexch_init OSSL_FUNC_KEYEXCH_INIT
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OP_keyexch_set_peer OSSL_FUNC_KEYEXCH_SET_PEER
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OP_keyexch_derive OSSL_FUNC_KEYEXCH_DERIVE
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OP_keyexch_set_ctx_params OSSL_FUNC_KEYEXCH_SET_CTX_PARAMS
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OP_keyexch_settable_ctx_params OSSL_FUNC_KEYEXCH_SETTABLE_CTX_PARAMS
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OP_keyexch_get_ctx_params OSSL_FUNC_KEYEXCH_GET_CTX_PARAMS
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OP_keyexch_gettable_ctx_params OSSL_FUNC_KEYEXCH_GETTABLE_CTX_PARAMS
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A key exchange algorithm implementation may not implement all of these functions.
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In order to be a consistent set of functions a provider must implement
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OP_keyexch_newctx, OP_keyexch_freectx, OP_keyexch_init and OP_keyexch_derive.
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All other functions are optional.
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A key exchange algorithm must also implement some mechanism for generating,
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loading or importing keys via the key management (OSSL_OP_KEYMGMT) operation.
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See L<provider-keymgmt(7)> for further details.
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=head2 Context Management Functions
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OP_keyexch_newctx() should create and return a pointer to a provider side
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structure for holding context information during a key exchange operation.
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A pointer to this context will be passed back in a number of the other key
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exchange operation function calls.
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The parameter I<provctx> is the provider context generated during provider
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initialisation (see L<provider(7)>).
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OP_keyexch_freectx() is passed a pointer to the provider side key exchange
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context in the I<ctx> parameter.
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This function should free any resources associated with that context.
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OP_keyexch_dupctx() should duplicate the provider side key exchange context in
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the I<ctx> parameter and return the duplicate copy.
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=head2 Shared Secret Derivation Functions
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OP_keyexch_init() initialises a key exchange operation given a provider side key
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exchange context in the I<ctx> parameter, and a pointer to a provider key object
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in the I<provkey> parameter. The key object should have been previously
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generated, loaded or imported into the provider using the key management
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(OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)>.
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OP_keyexch_set_peer() is called to supply the peer's public key (in the
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I<provkey> parameter) to be used when deriving the shared secret.
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It is also passed a previously initialised key exchange context in the I<ctx>
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parameter.
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The key object should have been previously generated, loaded or imported into
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the provider using the key management (OSSL_OP_KEYMGMT) operation (see
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provider-keymgmt(7)>.
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OP_keyexch_derive() performs the actual key exchange itself by deriving a shared
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secret.
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A previously initialised key exchange context is passed in the I<ctx>
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parameter.
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The derived secret should be written to the location I<secret> which should not
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exceed I<outlen> bytes.
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The length of the shared secret should be written to I<*secretlen>.
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If I<secret> is NULL then the maximum length of the shared secret should be
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written to I<*secretlen>.
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=head2 Key Exchange Parameters Functions
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OP_keyexch_set_ctx_params() sets key exchange parameters associated with the
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given provider side key exchange context I<ctx> to I<params>,
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see L</Key Exchange Parameters>.
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Any parameter settings are additional to any that were previously set.
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OP_keyexch_get_ctx_params() gets key exchange parameters associated with the
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given provider side key exchange context I<ctx> into I<params>,
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see L</Key Exchange Parameters>.
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OP_keyexch_settable_ctx_params() yields a constant B<OSSL_PARAM> array that
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describes the settable parameters, i.e. parameters that can be used with
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OP_signature_set_ctx_params().
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If OP_keyexch_settable_ctx_params() is present, OP_keyexch_set_ctx_params() must
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also be present, and vice versa.
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Similarly, OP_keyexch_gettable_ctx_params() yields a constant B<OSSL_PARAM>
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array that describes the gettable parameters, i.e. parameters that can be
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handled by OP_signature_get_ctx_params().
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If OP_keyexch_gettable_ctx_params() is present, OP_keyexch_get_ctx_params() must
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also be present, and vice versa.
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See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.
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Notice that not all settable parameters are also gettable, and vice versa.
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=head2 Key Exchange Parameters
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See L<OSSL_PARAM(3)> for further details on the parameters structure used by
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the OP_keyexch_set_ctx_params() and OP_keyexch_get_ctx_params() functions.
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Parameters currently recognised by built-in key exchange algorithms are as
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follows.
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Not all parameters are relevant to, or are understood by all key exchange
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algorithms:
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=over 4
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=item "pad" (B<OSSL_EXCHANGE_PARAM_PAD>) <unsigned integer>
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Sets the padding mode for the associated key exchange ctx.
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Setting a value of 1 will turn padding on.
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Setting a vlue of 0 will turn padding off.
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If padding is off then the derived shared secret may be smaller than the largest
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possible secret size.
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If padding is on then the derived shared secret will have its first bytes filled
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with 0s where necessary to make the shared secret the same size as the largest
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possible secret size.
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=item "ecdh-cofactor-mode" (B<OSSL_EXCHANGE_PARAM_EC_ECDH_COFACTOR_MODE>) <integer>
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Sets/gets the ECDH mode of operation for the associated key exchange ctx.
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In the context of an Elliptic Curve Diffie-Hellman key exchange, this parameter
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can be used to select between the plain Diffie-Hellman (DH) or Cofactor
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Diffie-Hellman (CDH) variants of the key exchange algorithm.
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When setting, the value should be 1, 0 or -1, respectively forcing cofactor mode
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on, off, or resetting it to the default for the private key associated with the
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given key exchange ctx.
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When getting, the value should be either 1 or 0, respectively signaling if the
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cofactor mode is on or off.
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See also L<provider-keymgmt(7)> for the related
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B<OSSL_PKEY_PARAM_USE_COFACTOR_ECDH> parameter that can be set on a
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per-key basis.
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=item "kdf-type" (B<OSSL_EXCHANGE_PARAM_KDF_TYPE>) <utf8_string>
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Sets/gets the Key Derivation Function type to apply within the associated key
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exchange ctx.
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=item "kdf-digest" (B<OSSL_EXCHANGE_PARAM_KDF_DIGEST>) <utf8_string>
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Sets/gets the Digest algorithm to be used as part of the Key Derivation Function
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associated with the given key exchange ctx.
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=item "kdf-digest-props" (B<OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS>) <utf8_string>
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Sets properties to be used upon look up of the implementation for the selected
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Digest algorithm for the Key Derivation Function associated with the given key
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exchange ctx.
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=item "kdf-outlen" (B<OSSL_EXCHANGE_PARAM_KDF_OUTLEN>) <size_t>
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Sets/gets the desired size for the output of the chosen Key Derivation Function
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associated with the given key exchange ctx.
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=item "kdf-ukm" (B<OSSL_EXCHANGE_PARAM_KDF_UKM>) <octet_string>
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Sets/gets User Key Material to be used as part of the selected Key Derivation
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Function associated with the given key exchange ctx.
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=item "kdf-ukm-len" (B<OSSL_EXCHANGE_PARAM_KDF_UKM_LEN>) <size_t>
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Sets/gets the size of the User Key Material to be used as part of the selected
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Key Derivation Function associated with the given key exchange ctx.
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=back
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=head1 RETURN VALUES
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OP_keyexch_newctx() and OP_keyexch_dupctx() should return the newly created
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provider side key exchange context, or NULL on failure.
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OP_keyexch_init(), OP_keyexch_set_peer(), OP_keyexch_derive(),
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OP_keyexch_set_params(), and OP_keyexch_get_params() should return 1 for success
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or 0 on error.
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OP_keyexch_settable_ctx_params() and OP_keyexch_gettable_ctx_params() should
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always return a constant B<OSSL_PARAM> array.
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=head1 SEE ALSO
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L<provider(7)>
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=head1 HISTORY
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The provider KEYEXCH interface was introduced in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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