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EVP_KEYEXCH-ECDH

NAME

EVP_KEYEXCH-ECDH - ECDH Key Exchange algorithm support

DESCRIPTION

Key exchange support for the ECDH key type.

ECDH Key Exchange parameters

EXAMPLES

Examples of key agreement can be found in demos/keyexch.

Keys for the host and peer must be generated as shown in "Examples" in EVP_PKEY-EC(7) using the same curve name.

The code to generate a shared secret for the normal case is identical to "Examples" in EVP_KEYEXCH-DH(7).

To derive a shared secret on the host using the host's key and the peer's public key but also using X963KDF with a user key material:

/* It is assumed that the host_key, peer_pub_key and ukm are set up */
void derive_secret(EVP_PKEY *host_key, EVP_PKEY *peer_key,
                   unsigned char *ukm, size_t ukm_len)
{
    unsigned char secret[64];
    size_t out_len = sizeof(secret);
    size_t secret_len = out_len;
    unsigned int pad = 1;
    OSSL_PARAM params[6];
    EVP_PKEY_CTX *dctx = EVP_PKEY_CTX_new_from_pkey(NULL, host_key, NULL);

    EVP_PKEY_derive_init(dctx);

    params[0] = OSSL_PARAM_construct_uint(OSSL_EXCHANGE_PARAM_PAD, &pad);
    params[1] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_TYPE,
                                                 "X963KDF", 0);
    params[2] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_DIGEST,
                                                 "SHA1", 0);
    params[3] = OSSL_PARAM_construct_size_t(OSSL_EXCHANGE_PARAM_KDF_OUTLEN,
                                            &out_len);
    params[4] = OSSL_PARAM_construct_octet_string(OSSL_EXCHANGE_PARAM_KDF_UKM,
                                                  ukm, ukm_len);
    params[5] = OSSL_PARAM_construct_end();
    EVP_PKEY_CTX_set_params(dctx, params);

    EVP_PKEY_derive_set_peer(dctx, peer_pub_key);
    EVP_PKEY_derive(dctx, secret, &secret_len);
    ...
    OPENSSL_clear_free(secret, secret_len);
    EVP_PKEY_CTX_free(dctx);
}

SEE ALSO

EVP_PKEY-EC(7)EVP_PKEY(3), provider-keyexch(7), provider-keymgmt(7), OSSL_PROVIDER-default(7), OSSL_PROVIDER-FIPS(7),

Copyright 2020-2024 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.