=pod

=head1 NAME

dh - Diffie-Hellman key agreement

=head1 SYNOPSIS

 #include <openssl/dh.h>
 #include <openssl/engine.h>

 DH *   DH_new(void);
 void   DH_free(DH *dh);

 DH *   DH_generate_parameters(int prime_len, int generator,
                void (*callback)(int, int, void *), void *cb_arg);
 int    DH_check(const DH *dh, int *codes);

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

 void DH_set_default_method(const DH_METHOD *meth);
 const DH_METHOD *DH_get_default_method(void);
 int DH_set_method(DH *dh, const DH_METHOD *meth);
 DH *DH_new_method(ENGINE *engine);
 const DH_METHOD *DH_OpenSSL(void);

 DH *   d2i_DHparams(DH **a, unsigned char **pp, long length);
 int    i2d_DHparams(const DH *a, unsigned char **pp);

 int    DHparams_print_fp(FILE *fp, const DH *x);
 int    DHparams_print(BIO *bp, const DH *x);

=head1 DESCRIPTION

These functions implement the Diffie-Hellman key agreement protocol.
The generation of shared DH parameters is described in
L<DH_generate_parameters(3)>; L<DH_generate_key(3)> describes how
to perform a key agreement.

The B<DH> structure consists of several BIGNUM components. The prime B<p>, the
generate B<g>, the Private key B<priv_key> and the public key B<pub_key>.
Optionally there may also be an additional parameter B<q>.

Note that DH keys may use non-standard B<DH_METHOD> implementations,
either directly or by the use of B<ENGINE> modules. In some cases (eg. an
ENGINE providing support for hardware-embedded keys), these BIGNUM values
will not be used by the implementation or may be used for alternative data
storage.

=head1 SEE ALSO

L<dhparam(1)>, L<bn(3)>, L<dsa(3)>, L<err(3)>,
L<rand(3)>, L<rsa(3)>, L<engine(3)>,
L<DH_set_method(3)>, L<DH_new(3)>,
L<DH_get_ex_new_index(3)>,
L<DH_generate_parameters(3)>,
L<DH_compute_key(3)>, L<DH_get0_pqg(3)>, L<DH_meth_new(3)>, L<d2i_DHparams(3)>,
L<RSA_print(3)>

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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
L<https://www.openssl.org/source/license.html>.

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