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DH_generate_key(3)                  OpenSSL                 DH_generate_key(3)



NAME
       DH_generate_key, DH_compute_key, DH_compute_key_padded - perform
       Diffie-Hellman key exchange

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/dh.h>

       The following functions have been deprecated since OpenSSL 3.0, and can
       be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
       version value, see openssl_user_macros(7):

        int DH_generate_key(DH *dh);

        int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);

        int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh);

DESCRIPTION
       All of the functions described on this page are deprecated.
       Applications should instead use EVP_PKEY_derive_init(3) and
       EVP_PKEY_derive(3).

       DH_generate_key() performs the first step of a Diffie-Hellman key
       exchange by generating private and public DH values. By calling
       DH_compute_key() or DH_compute_key_padded(), these are combined with
       the other party's public value to compute the shared key.

       DH_generate_key() expects dh to contain the shared parameters dh->p and
       dh->g. It generates a random private DH value unless dh->priv_key is
       already set, and computes the corresponding public value dh->pub_key,
       which can then be published.

       DH_compute_key() computes the shared secret from the private DH value
       in dh and the other party's public value in pub_key and stores it in
       key. key must point to DH_size(dh) bytes of memory.  The padding style
       is RFC 5246 (8.1.2) that strips leading zero bytes.  It is not constant
       time due to the leading zero bytes being stripped.  The return value
       should be considered public.

       DH_compute_key_padded() is similar but stores a fixed number of bytes.
       The padding style is NIST SP 800-56A (C.1) that retains leading zero
       bytes.  It is constant time due to the leading zero bytes being
       retained.  The return value should be considered public.

RETURN VALUES
       DH_generate_key() returns 1 on success, 0 otherwise.

       DH_compute_key() returns the size of the shared secret on success, -1
       on error.

       DH_compute_key_padded() returns DH_size(dh) on success, -1 on error.

       The error codes can be obtained by ERR_get_error(3).

SEE ALSO
       EVP_PKEY_derive(3), DH_new(3), ERR_get_error(3), RAND_bytes(3),
       DH_size(3)

HISTORY
       DH_compute_key_padded() was added in OpenSSL 1.0.2.

       All of these functions were deprecated in OpenSSL 3.0.

COPYRIGHT
       Copyright 2000-2021 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>.



3.0.12                            2023-05-07                DH_generate_key(3)