mirror of https://github.com/openssl/openssl.git
92 lines
3.8 KiB
Plaintext
92 lines
3.8 KiB
Plaintext
=pod
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=head1 NAME
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SSL_export_keying_material,
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SSL_export_keying_material_early
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- obtain keying material for application use
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
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const char *label, size_t llen,
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const unsigned char *context,
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size_t contextlen, int use_context);
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int SSL_export_keying_material_early(SSL *s, unsigned char *out, size_t olen,
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const char *label, size_t llen,
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const unsigned char *context,
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size_t contextlen);
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=head1 DESCRIPTION
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During the creation of a TLS or DTLS connection shared keying material is
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established between the two endpoints. The functions
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SSL_export_keying_material() and SSL_export_keying_material_early() enable an
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application to use some of this keying material for its own purposes in
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accordance with RFC5705 (for TLSv1.2 and below) or RFC8446 (for TLSv1.3).
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SSL_export_keying_material() derives keying material using
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the F<exporter_master_secret> established in the handshake.
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SSL_export_keying_material_early() is only usable with TLSv1.3, and derives
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keying material using the F<early_exporter_master_secret> (as defined in the
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TLS 1.3 RFC). For the client, the F<early_exporter_master_secret> is only
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available when the client attempts to send 0-RTT data. For the server, it is
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only available when the server accepts 0-RTT data.
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An application may need to securely establish the context within which this
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keying material will be used. For example this may include identifiers for the
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application session, application algorithms or parameters, or the lifetime of
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the context. The context value is left to the application but must be the same
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on both sides of the communication.
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For a given SSL connection B<s>, B<olen> bytes of data will be written to
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B<out>. The application specific context should be supplied in the location
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pointed to by B<context> and should be B<contextlen> bytes long. Provision of
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a context is optional. If the context should be omitted entirely then
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B<use_context> should be set to 0. Otherwise it should be any other value. If
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B<use_context> is 0 then the values of B<context> and B<contextlen> are ignored.
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Note that in TLSv1.2 and below a zero length context is treated differently from
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no context at all, and will result in different keying material being returned.
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In TLSv1.3 a zero length context is that same as no context at all and will
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result in the same keying material being returned.
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An application specific label should be provided in the location pointed to by
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B<label> and should be B<llen> bytes long. Typically this will be a value from
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the IANA Exporter Label Registry
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(L<https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels>).
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Alternatively labels beginning with "EXPERIMENTAL" are permitted by the standard
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to be used without registration. TLSv1.3 imposes a maximum label length of
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249 bytes.
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Note that this function is only defined for TLSv1.0 and above, and DTLSv1.0 and
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above. Attempting to use it in SSLv3 will result in an error.
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=head1 RETURN VALUES
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SSL_export_keying_material() returns 0 or -1 on failure or 1 on success.
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SSL_export_keying_material_early() returns 0 on failure or 1 on success.
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=head1 SEE ALSO
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L<ssl(7)>
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=head1 HISTORY
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The SSL_export_keying_material_early() function was added in OpenSSL 1.1.1.
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=head1 COPYRIGHT
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Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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