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=head1 NAME

DH_generate_key, DH_compute_key - perform Diffie-Hellman key exchange

=head1 SYNOPSIS

 #include <openssl/dh.h>

 int DH_generate_key(DH *dh);

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

=head1 DESCRIPTION

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(), these are combined with the other party's public
value to compute the shared key.

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

DH_compute_key() computes the shared secret from the private DH value
in B<dh> and the other party's public value in B<pub_key> and stores
it in B<key>. B<key> must point to B<DH_size(dh)> bytes of memory.

=head1 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.

The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.

=head1 SEE ALSO

L<dh(3)|dh(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>, L<DH_size(3)|DH_size(3)>

=head1 HISTORY

DH_generate_key() and DH_compute_key() are available in all versions
of SSLeay and OpenSSL.

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