1DH_GENERATE_KEY(3)                  OpenSSL                 DH_GENERATE_KEY(3)
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NAME

6       DH_generate_key, DH_compute_key, DH_compute_key_padded - perform
7       Diffie-Hellman key exchange
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SYNOPSIS

10        #include <openssl/dh.h>
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12        int DH_generate_key(DH *dh);
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14        int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
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16        int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh);
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DESCRIPTION

19       DH_generate_key() performs the first step of a Diffie-Hellman key
20       exchange by generating private and public DH values. By calling
21       DH_compute_key() or DH_compute_key_padded(), these are combined with
22       the other party's public value to compute the shared key.
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24       DH_generate_key() expects dh to contain the shared parameters dh->p and
25       dh->g. It generates a random private DH value unless dh->priv_key is
26       already set, and computes the corresponding public value dh->pub_key,
27       which can then be published.
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29       DH_compute_key() computes the shared secret from the private DH value
30       in dh and the other party's public value in pub_key and stores it in
31       key. key must point to DH_size(dh) bytes of memory.  The padding style
32       is RFC 5246 (8.1.2) that strips leading zero bytes.  It is not constant
33       time due to the leading zero bytes being stripped.  The return value
34       should be considered public.
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36       DH_compute_key_padded() is similar but stores a fixed number of bytes.
37       The padding style is NIST SP 800-56A (C.1) that retains leading zero
38       bytes.  It is constant time due to the leading zero bytes being
39       retained.  The return value should be considered public.
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RETURN VALUES

42       DH_generate_key() returns 1 on success, 0 otherwise.
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44       DH_compute_key() returns the size of the shared secret on success, -1
45       on error.
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47       DH_compute_key_padded() returns DH_size(dh) on success, -1 on error.
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49       The error codes can be obtained by ERR_get_error(3).
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SEE ALSO

52       DH_new(3), ERR_get_error(3), RAND_bytes(3), DH_size(3)
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HISTORY

55       DH_compute_key_padded() was added in OpenSSL 1.0.2.
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58       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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60       Licensed under the OpenSSL license (the "License").  You may not use
61       this file except in compliance with the License.  You can obtain a copy
62       in the file LICENSE in the source distribution or at
63       <https://www.openssl.org/source/license.html>.
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671.1.1q                            2023-02-06                DH_GENERATE_KEY(3)
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