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Improved HKDF and TLS1-PRF documentation 

Reviewed-by: Rich Salz <rsalz@openssl.org>
This commit is contained in:
Viktor Dukhovni 2016-03-03 23:30:42 -05:00
parent c8cca980dc
commit f04abe7d50
3 changed files with 37 additions and 15 deletions
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13
doc/apps/pkeyutl.pod
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@ -123,12 +123,15 @@ derive a shared secret using the peer key.
=item B<-kdf algorithm>
Use key derivation function B<algorithm>. Note: additional paramers
will normally have to be set and the KDF output length for this to work.
Use key derivation function B<algorithm>. The supported algorithms are
at present B<TLS1-PRF> and B<HKDF>.
Note: additional paramers and the KDF output length will normally have to be
set for this to work. See L<EVP_PKEY_HKDF(3)> and L<EVP_PKEY_TLS1_PRF(3)>
for the supported string parameters of each algorithm.
=item B<-kdflen length>
Set the ouput length for KDF.
Set the output length for KDF.
=item B<-pkeyopt opt:value>
@ -155,7 +158,6 @@ for all available algorithms.
When used with the B<-engine> option, it specifies to also use
engine B<id> for crypto operations.
=back
=head1 NOTES
@ -269,4 +271,5 @@ seed consisting of the single byte 0xFF.
=head1 SEE ALSO
L<genpkey(1)>, L<pkey(1)>, L<rsautl(1)>
L<dgst(1)>, L<rsa(1)>, L<genrsa(1)>
L<dgst(1)>, L<rsa(1)>, L<genrsa(1)>,
L<EVP_PKEY_HKDF(3)>, L<EVP_PKEY_TLS1_PRF(3)>

26
doc/crypto/EVP_PKEY_HKDF.pod
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@ -23,7 +23,7 @@ HMAC-based Extract-and-Expand key derivation algorithm
=head1 DESCRIPTION
The EVP_PKEY_HKDF alogorithm implements the HKDF key derivation function.
The EVP_PKEY_HKDF algorithm implements the HKDF key derivation function.
HKDF follows the "extract-then-expand" paradigm, where the KDF logically
consists of two modules. The first stage takes the input keying material
and "extracts" from it a fixed-length pseudorandom key K. The second stage
@ -42,6 +42,17 @@ EVP_PKEY_CTX_add1_hkdf_info() sets the info value to B<infolen> bytes of the
buffer B<info>. If a value is already set, it is appended to the existing
value.
=head1 STRING CTRLS
HKDF also supports string based control operations via
L<EVP_PKEY_CTX_ctrl_str(3)>.
The B<type> parameter "md" uses the supplied B<value> as the name of the digest
algorithm to use.
The B<type> parameters "salt", "key" and "info" use the supplied B<value>
parameter as a B<seed>, B<key> or B<info> value.
The names "hexsalt", "hexkey" and "hexinfo" are similar except they take a hex
string which is converted to binary.
=head1 NOTES
All these functions are implemented as macros.
@ -56,9 +67,13 @@ an error occurs.
The total length of the info buffer cannot exceed 1024 bytes in length: this
should be more than enough for any normal use of HKDF.
The output length of the KDF is specified by the length parameter in the
EVP_PKEY_derive() function. Since the output length is variable, setting
the buffer to B<NULL> is not meaningful for HKDF.
The output length of the KDF is specified via the length parameter to the
L<EVP_PKEY_derive(3)> function.
Since the HKDF output length is variable, passing a B<NULL> buffer as a means
to obtain the requisite length is not meaningful with HKDF.
Instead, the caller must allocate a buffer of the desired length, and pass that
buffer to L<EVP_PKEY_derive(3)> along with (a pointer initialized to) the
desired length.
Optimised versions of HKDF can be implemented in an ENGINE.
@ -98,6 +113,7 @@ RFC 5869
=head1 SEE ALSO
L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_derive(3)>,
L<EVP_PKEY_CTX_ctrl_str(3)>,
L<EVP_PKEY_derive(3)>
=cut

13
doc/crypto/EVP_PKEY_TLS1_PRF.pod
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@ -36,10 +36,13 @@ If a seed is already set it is appended to the existing value.
=head1 STRING CTRLS
The TLS PRF also supports string based control operations using
EVP_PKEY_CTX_ctrl_str(). The B<type> parameters "secret" and "seed" use
the supplied B<value> parameter as a secret or seed value. The names
"hexsecret" and "hexseed" are similar except they take a hex string which
is converted to binary.
L<EVP_PKEY_CTX_ctrl_str(3)>.
The B<type> parameter "md" uses the supplied B<value> as the name of the digest
algorithm to use.
The B<type> parameters "secret" and "seed" use the supplied B<value> parameter
as a secret or seed value.
The names "hexsecret" and "hexseed" are similar except they take a hex string
which is converted to binary.
=head1 NOTES
@ -90,7 +93,7 @@ and seed value "seed":
=head1 SEE ALSO
L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_CTX_ctrl(3)>,
L<EVP_PKEY_CTX_ctrl_str(3)>,
L<EVP_PKEY_derive(3)>
=cut