NetBSD-5.0.2/lib/libcrypto/man/DH_set_method.3
.\" $NetBSD: DH_set_method.3,v 1.21 2008/05/09 22:02:42 christos Exp $
.\"
.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.32
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.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. | will give a
.\" real vertical bar. \*(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-|\(bv\*(Tr
.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" ''
'br\}
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.if \nF \{\
. de IX
. tm Index:\\$1\t\\n%\t"\\$2"
..
. nr % 0
. rr F
.\}
.\"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.hy 0
.if n .na
.\"
.\" 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_set_method 3"
.TH DH_set_method 3 "2008-05-09" "0.9.9-dev" "OpenSSL"
.SH "NAME"
DH_set_default_method, DH_get_default_method,
DH_set_method, DH_new_method, DH_OpenSSL \- select DH method
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& #include <openssl/dh.h>
\& #include <openssl/engine.h>
.Ve
.PP
.Vb 1
\& void DH_set_default_method(const DH_METHOD *meth);
.Ve
.PP
.Vb 1
\& const DH_METHOD *DH_get_default_method(void);
.Ve
.PP
.Vb 1
\& int DH_set_method(DH *dh, const DH_METHOD *meth);
.Ve
.PP
.Vb 1
\& DH *DH_new_method(ENGINE *engine);
.Ve
.PP
.Vb 1
\& const DH_METHOD *DH_OpenSSL(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman
operations. By modifying the method, alternative implementations
such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for
important information about how these \s-1DH\s0 \s-1API\s0 functions are affected by the use
of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
.PP
Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as
returned by \fIDH_OpenSSL()\fR.
.PP
\&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0
structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set
as a default for \s-1DH\s0, so this function is no longer recommended.
.PP
\&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD\s0.
However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0
\&\s-1API\s0 is being used, so this function is no longer recommended.
.PP
\&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR.
This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method
was supplied by an \s-1ENGINE\s0, the handle to that \s-1ENGINE\s0 will be released during the
change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0
implementations (eg. from an \s-1ENGINE\s0 module that supports embedded
hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0
for the key can have unexpected results.
.PP
\&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will
be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL\s0, the default \s-1ENGINE\s0 for \s-1DH\s0
operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by
\&\fIDH_set_default_method()\fR is used.
.SH "THE DH_METHOD STRUCTURE"
.IX Header "THE DH_METHOD STRUCTURE"
.Vb 4
\& typedef struct dh_meth_st
\& {
\& /* name of the implementation */
\& const char *name;
.Ve
.PP
.Vb 2
\& /* generate private and public DH values for key agreement */
\& int (*generate_key)(DH *dh);
.Ve
.PP
.Vb 2
\& /* compute shared secret */
\& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);
.Ve
.PP
.Vb 4
\& /* compute r = a ^ p mod m (May be NULL for some implementations) */
\& int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p,
\& const BIGNUM *m, BN_CTX *ctx,
\& BN_MONT_CTX *m_ctx);
.Ve
.PP
.Vb 2
\& /* called at DH_new */
\& int (*init)(DH *dh);
.Ve
.PP
.Vb 2
\& /* called at DH_free */
\& int (*finish)(DH *dh);
.Ve
.PP
.Vb 1
\& int flags;
.Ve
.PP
.Vb 1
\& char *app_data; /* ?? */
.Ve
.PP
.Vb 1
\& } DH_METHOD;
.Ve
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIDH_OpenSSL()\fR and \fIDH_get_default_method()\fR return pointers to the respective
\&\fB\s-1DH_METHOD\s0\fRs.
.PP
\&\fIDH_set_default_method()\fR returns no value.
.PP
\&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as
the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous
method was supplied by an \s-1ENGINE\s0).
.PP
\&\fIDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by
\&\fIERR_get_error\fR\|(3) if the allocation fails. Otherwise it
returns a pointer to the newly allocated structure.
.SH "NOTES"
.IX Header "NOTES"
As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other
algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
that will override any \s-1DH\s0 defaults set using the \s-1DH\s0 \s-1API\s0 (ie.
\&\fIDH_set_default_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
to control default implementations for use in \s-1DH\s0 and other cryptographic
algorithms.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIopenssl_dh\fR\|(3), \fIDH_new\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIDH_set_default_method()\fR, \fIDH_get_default_method()\fR, \fIDH_set_method()\fR,
\&\fIDH_new_method()\fR and \fIDH_OpenSSL()\fR were added in OpenSSL 0.9.4.
.PP
\&\fIDH_set_default_openssl_method()\fR and \fIDH_get_default_openssl_method()\fR replaced
\&\fIDH_set_default_method()\fR and \fIDH_get_default_method()\fR respectively, and
\&\fIDH_set_method()\fR and \fIDH_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than
\&\fB\s-1DH_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For
0.9.7, the handling of defaults in the \s-1ENGINE\s0 \s-1API\s0 was restructured so that this
change was reversed, and behaviour of the other functions resembled more closely
the previous behaviour. The behaviour of defaults in the \s-1ENGINE\s0 \s-1API\s0 now
transparently overrides the behaviour of defaults in the \s-1DH\s0 \s-1API\s0 without
requiring changing these function prototypes.