????
Your IP : 3.139.70.69
.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35)
.\"
.\" 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 >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'.
.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 "EVP_PKEY_CTX_SET_HKDF_MD 3"
.TH EVP_PKEY_CTX_SET_HKDF_MD 3 "2023-09-11" "1.1.1w" "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"
EVP_PKEY_CTX_set_hkdf_md, EVP_PKEY_CTX_set1_hkdf_salt, EVP_PKEY_CTX_set1_hkdf_key, EVP_PKEY_CTX_add1_hkdf_info, EVP_PKEY_CTX_hkdf_mode \- HMAC\-based Extract\-and\-Expand key derivation algorithm
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/kdf.h>
\&
\& int EVP_PKEY_CTX_hkdf_mode(EVP_PKEY_CTX *pctx, int mode);
\&
\& int EVP_PKEY_CTX_set_hkdf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md);
\&
\& int EVP_PKEY_CTX_set1_hkdf_salt(EVP_PKEY_CTX *pctx, unsigned char *salt,
\& int saltlen);
\&
\& int EVP_PKEY_CTX_set1_hkdf_key(EVP_PKEY_CTX *pctx, unsigned char *key,
\& int keylen);
\&
\& int EVP_PKEY_CTX_add1_hkdf_info(EVP_PKEY_CTX *pctx, unsigned char *info,
\& int infolen);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP_PKEY_HKDF\s0 algorithm implements the \s-1HKDF\s0 key derivation function.
\&\s-1HKDF\s0 follows the \*(L"extract-then-expand\*(R" paradigm, where the \s-1KDF\s0 logically
consists of two modules. The first stage takes the input keying material
and \*(L"extracts\*(R" from it a fixed-length pseudorandom key K. The second stage
\&\*(L"expands\*(R" the key K into several additional pseudorandom keys (the output
of the \s-1KDF\s0).
.PP
\&\fBEVP_PKEY_CTX_hkdf_mode()\fR sets the mode for the \s-1HKDF\s0 operation. There are three
modes that are currently defined:
.IP "\s-1EVP_PKEY_HKDEF_MODE_EXTRACT_AND_EXPAND\s0" 4
.IX Item "EVP_PKEY_HKDEF_MODE_EXTRACT_AND_EXPAND"
This is the default mode. Calling \fBEVP_PKEY_derive\fR\|(3) on an \s-1EVP_PKEY_CTX\s0 set
up for \s-1HKDF\s0 will perform an extract followed by an expand operation in one go.
The derived key returned will be the result after the expand operation. The
intermediate fixed-length pseudorandom key K is not returned.
.Sp
In this mode the digest, key, salt and info values must be set before a key is
derived or an error occurs.
.IP "\s-1EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY\s0" 4
.IX Item "EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY"
In this mode calling \fBEVP_PKEY_derive\fR\|(3) will just perform the extract
operation. The value returned will be the intermediate fixed-length pseudorandom
key K.
.Sp
The digest, key and salt values must be set before a key is derived or an
error occurs.
.IP "\s-1EVP_PKEY_HKDEF_MODE_EXPAND_ONLY\s0" 4
.IX Item "EVP_PKEY_HKDEF_MODE_EXPAND_ONLY"
In this mode calling \fBEVP_PKEY_derive\fR\|(3) will just perform the expand
operation. The input key should be set to the intermediate fixed-length
pseudorandom key K returned from a previous extract operation.
.Sp
The digest, key and info values must be set before a key is derived or an
error occurs.
.PP
\&\fBEVP_PKEY_CTX_set_hkdf_md()\fR sets the message digest associated with the \s-1HKDF.\s0
.PP
\&\fBEVP_PKEY_CTX_set1_hkdf_salt()\fR sets the salt to \fBsaltlen\fR bytes of the
buffer \fBsalt\fR. Any existing value is replaced.
.PP
\&\fBEVP_PKEY_CTX_set1_hkdf_key()\fR sets the key to \fBkeylen\fR bytes of the buffer
\&\fBkey\fR. Any existing value is replaced.
.PP
\&\fBEVP_PKEY_CTX_add1_hkdf_info()\fR sets the info value to \fBinfolen\fR bytes of the
buffer \fBinfo\fR. If a value is already set, it is appended to the existing
value.
.SH "STRING CTRLS"
.IX Header "STRING CTRLS"
\&\s-1HKDF\s0 also supports string based control operations via
\&\fBEVP_PKEY_CTX_ctrl_str\fR\|(3).
The \fBtype\fR parameter \*(L"md\*(R" uses the supplied \fBvalue\fR as the name of the digest
algorithm to use.
The \fBtype\fR parameter \*(L"mode\*(R" uses the values \*(L"\s-1EXTRACT_AND_EXPAND\*(R",
\&\*(L"EXTRACT_ONLY\*(R"\s0 and \*(L"\s-1EXPAND_ONLY\*(R"\s0 to determine the mode to use.
The \fBtype\fR parameters \*(L"salt\*(R", \*(L"key\*(R" and \*(L"info\*(R" use the supplied \fBvalue\fR
parameter as a \fBseed\fR, \fBkey\fR or \fBinfo\fR value.
The names \*(L"hexsalt\*(R", \*(L"hexkey\*(R" and \*(L"hexinfo\*(R" are similar except they take a hex
string which is converted to binary.
.SH "NOTES"
.IX Header "NOTES"
All these functions are implemented as macros.
.PP
A context for \s-1HKDF\s0 can be obtained by calling:
.PP
.Vb 1
\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
.Ve
.PP
The total length of the info buffer cannot exceed 1024 bytes in length: this
should be more than enough for any normal use of \s-1HKDF.\s0
.PP
The output length of an \s-1HKDF\s0 expand operation is specified via the length
parameter to the \fBEVP_PKEY_derive\fR\|(3) function.
Since the \s-1HKDF\s0 output length is variable, passing a \fB\s-1NULL\s0\fR buffer as a means
to obtain the requisite length is not meaningful with \s-1HKDF\s0 in any mode that
performs an expand operation. Instead, the caller must allocate a buffer of the
desired length, and pass that buffer to \fBEVP_PKEY_derive\fR\|(3) along with (a
pointer initialized to) the desired length. Passing a \fB\s-1NULL\s0\fR buffer to obtain
the length is allowed when using \s-1EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY.\s0
.PP
Optimised versions of \s-1HKDF\s0 can be implemented in an \s-1ENGINE.\s0
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
All these functions return 1 for success and 0 or a negative value for failure.
In particular a return value of \-2 indicates the operation is not supported by
the public key algorithm.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example derives 10 bytes using \s-1SHA\-256\s0 with the secret key \*(L"secret\*(R",
salt value \*(L"salt\*(R" and info value \*(L"label\*(R":
.PP
.Vb 4
\& EVP_PKEY_CTX *pctx;
\& unsigned char out[10];
\& size_t outlen = sizeof(out);
\& pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
\&
\& if (EVP_PKEY_derive_init(pctx) <= 0)
\& /* Error */
\& if (EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256()) <= 0)
\& /* Error */
\& if (EVP_PKEY_CTX_set1_hkdf_salt(pctx, "salt", 4) <= 0)
\& /* Error */
\& if (EVP_PKEY_CTX_set1_hkdf_key(pctx, "secret", 6) <= 0)
\& /* Error */
\& if (EVP_PKEY_CTX_add1_hkdf_info(pctx, "label", 5) <= 0)
\& /* Error */
\& if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
\& /* Error */
.Ve
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1RFC 5869\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_CTX_ctrl_str\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2016\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
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>.