xref: /freebsd/secure/lib/libcrypto/man/man3/DH_generate_key.3 (revision d9a42747950146bf03cda7f6e25d219253f8a57a)
Automatically generated by Pod::Man 4.14 (Pod::Simple 3.40)

Standard preamble:
========================================================================
..
..
.. 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 -- \(*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\} . 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.

If the F register is >0, 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'.
.. .nr rF 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 . ds #H 0 . ds #V .8m . ds #F .3m . ds #[ \f1 . ds #] .\} . ds #H ((1u-(\\\\n(.fu%2u))*.13m) . ds #V .6m . ds #F 0 . ds #[ \& . ds #] \& .\} . \" simple accents for nroff and troff . ds ' \& . ds ` \& . ds ^ \& . ds , \& . ds ~ ~ . ds / .\} . 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 . \" corrections for vroff . \" for low resolution devices (crt and lpr) \{\ . 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 .\} ========================================================================

Title "DH_GENERATE_KEY 3"
DH_GENERATE_KEY 3 "2023-02-07" "1.1.1t" "OpenSSL"
For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
"NAME"
DH_generate_key, DH_compute_key, DH_compute_key_padded - perform Diffie-Hellman key exchange
"SYNOPSIS"
Header "SYNOPSIS" .Vb 1 #include <openssl/dh.h> \& int DH_generate_key(DH *dh); \& int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh); \& int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh); .Ve
"DESCRIPTION"
Header "DESCRIPTION" \fBDH_generate_key() performs the first step of a Diffie-Hellman key exchange by generating private and public \s-1DH\s0 values. By calling \fBDH_compute_key() or DH_compute_key_padded(), these are combined with the other party's public value to compute the shared key.

\fBDH_generate_key() expects dh to contain the shared parameters \fBdh->p and dh->g. It generates a random private \s-1DH\s0 value unless dh->priv_key is already set, and computes the corresponding public value dh->pub_key, which can then be published.

\fBDH_compute_key() computes the shared secret from the private \s-1DH\s0 value in dh and the other party's public value in pub_key and stores it in key. key must point to DH_size(dh) bytes of memory. The padding style is \s-1RFC 5246\s0 (8.1.2) that strips leading zero bytes. It is not constant time due to the leading zero bytes being stripped. The return value should be considered public.

\fBDH_compute_key_padded() is similar but stores a fixed number of bytes. The padding style is \s-1NIST SP 800-56A\s0 (C.1) that retains leading zero bytes. It is constant time due to the leading zero bytes being retained. The return value should be considered public.

"RETURN VALUES"
Header "RETURN VALUES" \fBDH_generate_key() returns 1 on success, 0 otherwise.

\fBDH_compute_key() returns the size of the shared secret on success, -1 on error.

\fBDH_compute_key_padded() returns DH_size(dh) on success, -1 on error.

The error codes can be obtained by ERR_get_error\|(3).

"SEE ALSO"
Header "SEE ALSO" \fBDH_new\|(3), ERR_get_error\|(3), RAND_bytes\|(3), DH_size\|(3)
"HISTORY"
Header "HISTORY" \fBDH_compute_key_padded() was added in OpenSSL 1.0.2.
"COPYRIGHT"
Header "COPYRIGHT" Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.