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/*
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* Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
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*
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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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* https://www.openssl.org/source/license.html
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*/
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#include <openssl/core_names.h>
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#include <openssl/objects.h>
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#include <openssl/params.h>
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#include "crypto/bn.h"
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#include "crypto/ec.h"
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/*
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* The intention with the "backend" source file is to offer backend support
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* for legacy backends (EVP_PKEY_ASN1_METHOD and EVP_PKEY_METHOD) and provider
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* implementations alike.
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*/
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int ec_set_param_ecdh_cofactor_mode(EC_KEY *ec, const OSSL_PARAM *p)
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{
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const EC_GROUP *ecg = EC_KEY_get0_group(ec);
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const BIGNUM *cofactor;
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int mode;
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if (!OSSL_PARAM_get_int(p, &mode))
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return 0;
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/*
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* mode can be only 0 for disable, or 1 for enable here.
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*
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* This is in contrast with the same parameter on an ECDH EVP_PKEY_CTX that
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* also supports mode == -1 with the meaning of "reset to the default for
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* the associated key".
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*/
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if (mode < 0 || mode > 1)
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return 0;
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if ((cofactor = EC_GROUP_get0_cofactor(ecg)) == NULL )
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return 0;
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/* ECDH cofactor mode has no effect if cofactor is 1 */
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if (BN_is_one(cofactor))
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return 1;
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if (mode == 1)
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EC_KEY_set_flags(ec, EC_FLAG_COFACTOR_ECDH);
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else if (mode == 0)
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EC_KEY_clear_flags(ec, EC_FLAG_COFACTOR_ECDH);
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return 1;
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}
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/*
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* Callers of ec_key_fromdata MUST make sure that ec_key_params_fromdata has
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* been called before!
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*
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* This function only gets the bare keypair, domain parameters and other
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* parameters are treated separately, and domain parameters are required to
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* define a keypair.
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*/
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int ec_key_fromdata(EC_KEY *ec, const OSSL_PARAM params[], int include_private)
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{
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const OSSL_PARAM *param_priv_key = NULL, *param_pub_key = NULL;
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BN_CTX *ctx = NULL;
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BIGNUM *priv_key = NULL;
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unsigned char *pub_key = NULL;
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size_t pub_key_len;
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const EC_GROUP *ecg = NULL;
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EC_POINT *pub_point = NULL;
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int ok = 0;
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ecg = EC_KEY_get0_group(ec);
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if (ecg == NULL)
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return 0;
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param_pub_key =
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OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_PUB_KEY);
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if (include_private)
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param_priv_key =
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OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_PRIV_KEY);
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ctx = BN_CTX_new_ex(ec_key_get_libctx(ec));
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if (ctx == NULL)
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goto err;
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/* OpenSSL decree: If there's a private key, there must be a public key */
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if (param_priv_key != NULL && param_pub_key == NULL)
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goto err;
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if (param_pub_key != NULL)
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if (!OSSL_PARAM_get_octet_string(param_pub_key,
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(void **)&pub_key, 0, &pub_key_len)
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|| (pub_point = EC_POINT_new(ecg)) == NULL
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|| !EC_POINT_oct2point(ecg, pub_point, pub_key, pub_key_len, ctx))
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goto err;
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if (param_priv_key != NULL && include_private) {
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int fixed_words;
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const BIGNUM *order;
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/*
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* Key import/export should never leak the bit length of the secret
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* scalar in the key.
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*
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* For this reason, on export we use padded BIGNUMs with fixed length.
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*
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* When importing we also should make sure that, even if short lived,
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* the newly created BIGNUM is marked with the BN_FLG_CONSTTIME flag as
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* soon as possible, so that any processing of this BIGNUM might opt for
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* constant time implementations in the backend.
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*
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* Setting the BN_FLG_CONSTTIME flag alone is never enough, we also have
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* to preallocate the BIGNUM internal buffer to a fixed public size big
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* enough that operations performed during the processing never trigger
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* a realloc which would leak the size of the scalar through memory
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* accesses.
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*
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* Fixed Length
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* ------------
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*
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* The order of the large prime subgroup of the curve is our choice for
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* a fixed public size, as that is generally the upper bound for
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* generating a private key in EC cryptosystems and should fit all valid
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* secret scalars.
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*
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* For padding on export we just use the bit length of the order
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* converted to bytes (rounding up).
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*
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* For preallocating the BIGNUM storage we look at the number of "words"
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* required for the internal representation of the order, and we
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* preallocate 2 extra "words" in case any of the subsequent processing
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* might temporarily overflow the order length.
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*/
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order = EC_GROUP_get0_order(ecg);
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if (order == NULL || BN_is_zero(order))
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goto err;
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fixed_words = bn_get_top(order) + 2;
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if ((priv_key = BN_secure_new()) == NULL)
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goto err;
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if (bn_wexpand(priv_key, fixed_words) == NULL)
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goto err;
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BN_set_flags(priv_key, BN_FLG_CONSTTIME);
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if (!OSSL_PARAM_get_BN(param_priv_key, &priv_key))
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goto err;
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}
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if (priv_key != NULL
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&& !EC_KEY_set_private_key(ec, priv_key))
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goto err;
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if (pub_point != NULL
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&& !EC_KEY_set_public_key(ec, pub_point))
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goto err;
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ok = 1;
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err:
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BN_CTX_free(ctx);
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BN_clear_free(priv_key);
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OPENSSL_free(pub_key);
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EC_POINT_free(pub_point);
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return ok;
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}
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int ec_key_domparams_fromdata(EC_KEY *ec, const OSSL_PARAM params[])
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{
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const OSSL_PARAM *param_ec_name;
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EC_GROUP *ecg = NULL;
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char *curve_name = NULL;
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int ok = 0;
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if (ec == NULL)
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return 0;
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param_ec_name = OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_EC_NAME);
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if (param_ec_name == NULL) {
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/* explicit parameters */
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/*
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* TODO(3.0): should we support explicit parameters curves?
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*/
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return 0;
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} else {
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/* named curve */
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int curve_nid;
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if (!OSSL_PARAM_get_utf8_string(param_ec_name, &curve_name, 0)
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|| curve_name == NULL
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|| (curve_nid = ec_curve_name2nid(curve_name)) == NID_undef)
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goto err;
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if ((ecg = EC_GROUP_new_by_curve_name_ex(ec_key_get_libctx(ec),
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curve_nid)) == NULL)
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goto err;
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}
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if (!EC_KEY_set_group(ec, ecg))
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goto err;
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/*
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* TODO(3.0): if the group has changed, should we invalidate the private and
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* public key?
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*/
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ok = 1;
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err:
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OPENSSL_free(curve_name);
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EC_GROUP_free(ecg);
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return ok;
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}
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int ec_key_otherparams_fromdata(EC_KEY *ec, const OSSL_PARAM params[])
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{
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const OSSL_PARAM *p;
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if (ec == NULL)
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return 0;
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p = OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_USE_COFACTOR_ECDH);
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if (p != NULL && !ec_set_param_ecdh_cofactor_mode(ec, p))
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return 0;
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return 1;
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}
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