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Title "DH_GENERATE_KEY 3ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
DH_generate_key, DH_compute_key, DH_compute_key_padded - perform Diffie-Hellman key exchange Header "SYNOPSIS" .Vb 1 #include <openssl/dh.h> .Ve

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining \s-1OPENSSL_API_COMPAT\s0 with a suitable version value, see openssl_user_macros\|(7):

.Vb 1 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); .Ve

Header "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).

\fBDH_generate_key() performs the first step of a Diffie-Hellman key exchange by generating private and public \s-1DH\s0 values. By calling \fBDH_compute_key() or DH_compute_key_padded(), these are combined with the other party's public value to compute the shared key.

\fBDH_generate_key() expects dh to contain the shared parameters \fBdh->p and dh->g. It generates a random private \s-1DH\s0 value unless dh->priv_key is already set, and computes the corresponding public value dh->pub_key, which can then be published.

\fBDH_compute_key() computes the shared secret from the private \s-1DH\s0 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 \s-1RFC 5246\s0 (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.

\fBDH_compute_key_padded() is similar but stores a fixed number of bytes. The padding style is \s-1NIST SP 800-56A\s0 (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.

Header "RETURN VALUES" \fBDH_generate_key() returns 1 on success, 0 otherwise.

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

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

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

Header "SEE ALSO" \fBEVP_PKEY_derive\|(3), \fBDH_new\|(3), ERR_get_error\|(3), RAND_bytes\|(3), DH_size\|(3) Header "HISTORY" \fBDH_compute_key_padded() was added in OpenSSL 1.0.2.

All of these functions were deprecated in OpenSSL 3.0.

Header "COPYRIGHT" Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.