1=pod 2 3=head1 NAME 4 5SSL_export_keying_material, 6SSL_export_keying_material_early 7- obtain keying material for application use 8 9=head1 SYNOPSIS 10 11 #include <openssl/ssl.h> 12 13 int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen, 14 const char *label, size_t llen, 15 const unsigned char *context, 16 size_t contextlen, int use_context); 17 18 int SSL_export_keying_material_early(SSL *s, unsigned char *out, size_t olen, 19 const char *label, size_t llen, 20 const unsigned char *context, 21 size_t contextlen); 22 23=head1 DESCRIPTION 24 25During the creation of a TLS or DTLS connection shared keying material is 26established between the two endpoints. The functions 27SSL_export_keying_material() and SSL_export_keying_material_early() enable an 28application to use some of this keying material for its own purposes in 29accordance with RFC5705 (for TLSv1.2 and below) or RFC8446 (for TLSv1.3). 30 31SSL_export_keying_material() derives keying material using 32the F<exporter_master_secret> established in the handshake. 33 34SSL_export_keying_material_early() is only usable with TLSv1.3, and derives 35keying material using the F<early_exporter_master_secret> (as defined in the 36TLS 1.3 RFC). For the client, the F<early_exporter_master_secret> is only 37available when the client attempts to send 0-RTT data. For the server, it is 38only available when the server accepts 0-RTT data. 39 40An application may need to securely establish the context within which this 41keying material will be used. For example this may include identifiers for the 42application session, application algorithms or parameters, or the lifetime of 43the context. The context value is left to the application but must be the same 44on both sides of the communication. 45 46For a given SSL connection B<s>, B<olen> bytes of data will be written to 47B<out>. The application specific context should be supplied in the location 48pointed to by B<context> and should be B<contextlen> bytes long. Provision of 49a context is optional. If the context should be omitted entirely then 50B<use_context> should be set to 0. Otherwise it should be any other value. If 51B<use_context> is 0 then the values of B<context> and B<contextlen> are ignored. 52Note that in TLSv1.2 and below a zero length context is treated differently from 53no context at all, and will result in different keying material being returned. 54In TLSv1.3 a zero length context is that same as no context at all and will 55result in the same keying material being returned. 56 57An application specific label should be provided in the location pointed to by 58B<label> and should be B<llen> bytes long. Typically this will be a value from 59the IANA Exporter Label Registry 60(L<https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels>). 61Alternatively labels beginning with "EXPERIMENTAL" are permitted by the standard 62to be used without registration. TLSv1.3 imposes a maximum label length of 63249 bytes. 64 65Note that this function is only defined for TLSv1.0 and above, and DTLSv1.0 and 66above. Attempting to use it in SSLv3 will result in an error. 67 68=head1 RETURN VALUES 69 70SSL_export_keying_material() returns 0 or -1 on failure or 1 on success. 71 72SSL_export_keying_material_early() returns 0 on failure or 1 on success. 73 74=head1 SEE ALSO 75 76L<ssl(7)> 77 78=head1 HISTORY 79 80The SSL_export_keying_material_early() function was added in OpenSSL 1.1.1. 81 82=head1 COPYRIGHT 83 84Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved. 85 86Licensed under the Apache License 2.0 (the "License"). You may not use 87this file except in compliance with the License. You can obtain a copy 88in the file LICENSE in the source distribution or at 89L<https://www.openssl.org/source/license.html>. 90 91=cut 92