mirror of https://github.com/openssl/openssl.git
216 lines
8.8 KiB
Plaintext
216 lines
8.8 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_dispatch.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 *OSSL_FUNC_keyexch_newctx(void *provctx);
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void OSSL_FUNC_keyexch_freectx(void *ctx);
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void *OSSL_FUNC_keyexch_dupctx(void *ctx);
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/* Shared secret derivation */
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int OSSL_FUNC_keyexch_init(void *ctx, void *provkey,
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const OSSL_PARAM params[]);
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int OSSL_FUNC_keyexch_set_peer(void *ctx, void *provkey);
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int OSSL_FUNC_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 OSSL_FUNC_keyexch_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
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const OSSL_PARAM *OSSL_FUNC_keyexch_settable_ctx_params(void *ctx,
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void *provctx);
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int OSSL_FUNC_keyexch_get_ctx_params(void *ctx, OSSL_PARAM params[]);
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const OSSL_PARAM *OSSL_FUNC_keyexch_gettable_ctx_params(void *ctx,
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void *provctx);
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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_FUNC_{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_FUNC_{name}>.
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For example, the "function" OSSL_FUNC_keyexch_newctx() has these:
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typedef void *(OSSL_FUNC_keyexch_newctx_fn)(void *provctx);
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static ossl_inline OSSL_FUNC_keyexch_newctx_fn
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OSSL_FUNC_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_dispatch.h(7)>, as follows:
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OSSL_FUNC_keyexch_newctx OSSL_FUNC_KEYEXCH_NEWCTX
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OSSL_FUNC_keyexch_freectx OSSL_FUNC_KEYEXCH_FREECTX
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OSSL_FUNC_keyexch_dupctx OSSL_FUNC_KEYEXCH_DUPCTX
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OSSL_FUNC_keyexch_init OSSL_FUNC_KEYEXCH_INIT
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OSSL_FUNC_keyexch_set_peer OSSL_FUNC_KEYEXCH_SET_PEER
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OSSL_FUNC_keyexch_derive OSSL_FUNC_KEYEXCH_DERIVE
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OSSL_FUNC_keyexch_set_ctx_params OSSL_FUNC_KEYEXCH_SET_CTX_PARAMS
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OSSL_FUNC_keyexch_settable_ctx_params OSSL_FUNC_KEYEXCH_SETTABLE_CTX_PARAMS
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OSSL_FUNC_keyexch_get_ctx_params OSSL_FUNC_KEYEXCH_GET_CTX_PARAMS
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OSSL_FUNC_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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OSSL_FUNC_keyexch_newctx, OSSL_FUNC_keyexch_freectx, OSSL_FUNC_keyexch_init and OSSL_FUNC_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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OSSL_FUNC_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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OSSL_FUNC_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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OSSL_FUNC_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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OSSL_FUNC_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.
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The I<params>, if not NULL, should be set on the context in a manner similar to
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using OSSL_FUNC_keyexch_set_params().
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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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OSSL_FUNC_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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OSSL_FUNC_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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OSSL_FUNC_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</Common Key Exchange parameters>.
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Any parameter settings are additional to any that were previously set.
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Passing NULL for I<params> should return true.
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OSSL_FUNC_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</Common Key Exchange parameters>.
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Passing NULL for I<params> should return true.
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OSSL_FUNC_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 OSSL_FUNC_keyexch_settable_ctx_params() is present, OSSL_FUNC_keyexch_set_ctx_params() must
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also be present, and vice versa.
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Similarly, OSSL_FUNC_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 OSSL_FUNC_keyexch_gettable_ctx_params() is present, OSSL_FUNC_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 Common 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 OSSL_FUNC_keyexch_set_ctx_params() and OSSL_FUNC_keyexch_get_ctx_params() functions.
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Common parameters currently recognised by built-in key exchange algorithms are
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as follows.
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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 value 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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=back
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=head1 RETURN VALUES
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OSSL_FUNC_keyexch_newctx() and OSSL_FUNC_keyexch_dupctx() should return the newly created
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provider side key exchange context, or NULL on failure.
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OSSL_FUNC_keyexch_init(), OSSL_FUNC_keyexch_set_peer(), OSSL_FUNC_keyexch_derive(),
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OSSL_FUNC_keyexch_set_params(), and OSSL_FUNC_keyexch_get_params() should return 1 for success
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or 0 on error.
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OSSL_FUNC_keyexch_settable_ctx_params() and OSSL_FUNC_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 2019-2021 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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