.\" Automatically generated by Pod::Man 2.27 (Pod::Simple 3.28)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
.    ds C`
.    ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{
.    if \nF \{
.        de IX
.        tm Index:\\$1\t\\n%\t"\\$2"
..
.        if !\nF==2 \{
.            nr % 0
.            nr F 2
.        \}
.    \}
.\}
.rr rF
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "dh 3"
.TH dh 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.
.if n .ad l
.nh
.SH "NAME"
dh \- Diffie\-Hellman key agreement
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& #include <openssl/dh.h>
\& #include <openssl/engine.h>
\&
\& DH *   DH_new(void);
\& void   DH_free(DH *dh);
\&
\& int    DH_size(const 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);
\&
\& int DH_get_ex_new_index(long argl, char *argp, int (*new_func)(),
\&             int (*dup_func)(), void (*free_func)());
\& int DH_set_ex_data(DH *d, int idx, char *arg);
\& char *DH_get_ex_data(DH *d, int idx);
\&
\& 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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
These functions implement the Diffie-Hellman key agreement protocol.
The generation of shared \s-1DH\s0 parameters is described in
\&\fIDH_generate_parameters\fR\|(3); \fIDH_generate_key\fR\|(3) describes how
to perform a key agreement.
.PP
The \fB\s-1DH\s0\fR structure consists of several \s-1BIGNUM\s0 components.
.PP
.Vb 9
\& struct
\&        {
\&        BIGNUM *p;              // prime number (shared)
\&        BIGNUM *g;              // generator of Z_p (shared)
\&        BIGNUM *priv_key;       // private DH value x
\&        BIGNUM *pub_key;        // public DH value g^x
\&        // ...
\&        };
\& DH
.Ve
.PP
Note that \s-1DH\s0 keys may use non-standard \fB\s-1DH_METHOD\s0\fR implementations,
either directly or by the use of \fB\s-1ENGINE\s0\fR modules. In some cases (eg. an
\&\s-1ENGINE\s0 providing support for hardware-embedded keys), these \s-1BIGNUM\s0 values
will not be used by the implementation or may be used for alternative data
storage. For this reason, applications should generally avoid using \s-1DH\s0
structure elements directly and instead use \s-1API\s0 functions to query or
modify keys.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIdhparam\fR\|(1), \fIbn\fR\|(3), \fIdsa\fR\|(3), \fIerr\fR\|(3),
\&\fIrand\fR\|(3), \fIrsa\fR\|(3), \fIengine\fR\|(3),
\&\fIDH_set_method\fR\|(3), \fIDH_new\fR\|(3),
\&\fIDH_get_ex_new_index\fR\|(3),
\&\fIDH_generate_parameters\fR\|(3),
\&\fIDH_compute_key\fR\|(3), \fId2i_DHparams\fR\|(3),
\&\fIRSA_print\fR\|(3)