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

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       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>.

3.5.0                                              2025-06-04                              DH_GENERATE_KEY(3SSL)

       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.

DH_compute_key_padded() was added in OpenSSL 1.0.2.

       All of these functions were deprecated in OpenSSL 3.0.

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

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).

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

        #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);