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.\" ========================================================================
.\"
.IX Title "DH_generate_key 3"
.TH DH_generate_key 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
DH_generate_key, DH_compute_key \- perform Diffie\-Hellman key exchange
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/dh.h>
\&
\& int DH_generate_key(DH *dh);
\&
\& int DH_compute_key(unsigned char *key, BIGNUM *pub_key, DH *dh);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBDH_generate_key()\fR performs the first step of a Diffie-Hellman key
exchange by generating private and public \s-1DH\s0 values. By calling
\&\fBDH_compute_key()\fR, these are combined with the other party's public
value to compute the shared key.
.PP
\&\fBDH_generate_key()\fR expects \fBdh\fR to contain the shared parameters
\&\fBdh\->p\fR and \fBdh\->g\fR. It generates a random private \s-1DH\s0 value
unless \fBdh\->priv_key\fR is already set, and computes the
corresponding public value \fBdh\->pub_key\fR, which can then be
published.
.PP
\&\fBDH_compute_key()\fR computes the shared secret from the private \s-1DH\s0 value
in \fBdh\fR and the other party's public value in \fBpub_key\fR and stores
it in \fBkey\fR. \fBkey\fR must point to \fBDH_size(dh)\fR bytes of memory.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBDH_generate_key()\fR returns 1 on success, 0 otherwise.
.PP
\&\fBDH_compute_key()\fR returns the size of the shared secret on success, \-1
on error.
.PP
The error codes can be obtained by \fBERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBdh\fR\|(3), \fBERR_get_error\fR\|(3), \fBrand\fR\|(3), \fBDH_size\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fBDH_generate_key()\fR and \fBDH_compute_key()\fR are available in all versions
of SSLeay and OpenSSL.