openssl (3.1.3)
Browse
Usage
VersionsSSL_EXPORT_KEYING_MATERIAL(3ossl) OpenSSL SSL_EXPORT_KEYING_MATERIAL(3ossl)
NAME
SSL_export_keying_material, SSL_export_keying_material_early - obtain keying material for application use
SYNOPSIS
#include <openssl/ssl.h>
int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
const char *label, size_t llen,
const unsigned char *context,
size_t contextlen, int use_context);
int SSL_export_keying_material_early(SSL *s, unsigned char *out, size_t olen,
const char *label, size_t llen,
const unsigned char *context,
size_t contextlen);
DESCRIPTION
During the creation of a TLS or DTLS connection shared keying material is established between the two endpoints.
The functions SSL_export_keying_material() and SSL_export_keying_material_early() enable an application to use
some of this keying material for its own purposes in accordance with RFC5705 (for TLSv1.2 and below) or RFC8446
(for TLSv1.3).
SSL_export_keying_material() derives keying material using the exporter_master_secret established in the
handshake.
SSL_export_keying_material_early() is only usable with TLSv1.3, and derives keying material using the
early_exporter_master_secret (as defined in the TLS 1.3 RFC). For the client, the early_exporter_master_secret is
only available when the client attempts to send 0-RTT data. For the server, it is only available when the server
accepts 0-RTT data.
An application may need to securely establish the context within which this keying material will be used. For
example this may include identifiers for the application session, application algorithms or parameters, or the
lifetime of the context. The context value is left to the application but must be the same on both sides of the
communication.
For a given SSL connection s, olen bytes of data will be written to out. The application specific context should
be supplied in the location pointed to by context and should be contextlen bytes long. Provision of a context is
optional. If the context should be omitted entirely then use_context should be set to 0. Otherwise it should be
any other value. If use_context is 0 then the values of context and contextlen are ignored. Note that in TLSv1.2
and below a zero length context is treated differently from no context at all, and will result in different
keying material being returned. In TLSv1.3 a zero length context is that same as no context at all and will
result in the same keying material being returned.
An application specific label should be provided in the location pointed to by label and should be llen bytes
long. Typically this will be a value from the IANA Exporter Label Registry
(<https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels>). Alternatively labels
beginning with "EXPERIMENTAL" are permitted by the standard to be used without registration. TLSv1.3 imposes a
maximum label length of 249 bytes.
Note that this function is only defined for TLSv1.0 and above, and DTLSv1.0 and above. Attempting to use it in
SSLv3 will result in an error.
RETURN VALUES
SSL_export_keying_material() returns 0 or -1 on failure or 1 on success.
SSL_export_keying_material_early() returns 0 on failure or 1 on success.
SEE ALSO
ssl(7)
HISTORY
The SSL_export_keying_material_early() function was added in OpenSSL 1.1.1.
COPYRIGHT
Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the
License. You can obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.1.3 2023-09-19 SSL_EXPORT_KEYING_MATERIAL(3ossl)
NAME
SSL_export_keying_material, SSL_export_keying_material_early - obtain keying material for application use
SYNOPSIS
#include <openssl/ssl.h>
int SSL_export_keying_material(SSL *s, unsigned char *out, size_t olen,
const char *label, size_t llen,
const unsigned char *context,
size_t contextlen, int use_context);
int SSL_export_keying_material_early(SSL *s, unsigned char *out, size_t olen,
const char *label, size_t llen,
const unsigned char *context,
size_t contextlen);
DESCRIPTION
During the creation of a TLS or DTLS connection shared keying material is established between the two endpoints.
The functions SSL_export_keying_material() and SSL_export_keying_material_early() enable an application to use
some of this keying material for its own purposes in accordance with RFC5705 (for TLSv1.2 and below) or RFC8446
(for TLSv1.3).
SSL_export_keying_material() derives keying material using the exporter_master_secret established in the
handshake.
SSL_export_keying_material_early() is only usable with TLSv1.3, and derives keying material using the
early_exporter_master_secret (as defined in the TLS 1.3 RFC). For the client, the early_exporter_master_secret is
only available when the client attempts to send 0-RTT data. For the server, it is only available when the server
accepts 0-RTT data.
An application may need to securely establish the context within which this keying material will be used. For
example this may include identifiers for the application session, application algorithms or parameters, or the
lifetime of the context. The context value is left to the application but must be the same on both sides of the
communication.
For a given SSL connection s, olen bytes of data will be written to out. The application specific context should
be supplied in the location pointed to by context and should be contextlen bytes long. Provision of a context is
optional. If the context should be omitted entirely then use_context should be set to 0. Otherwise it should be
any other value. If use_context is 0 then the values of context and contextlen are ignored. Note that in TLSv1.2
and below a zero length context is treated differently from no context at all, and will result in different
keying material being returned. In TLSv1.3 a zero length context is that same as no context at all and will
result in the same keying material being returned.
An application specific label should be provided in the location pointed to by label and should be llen bytes
long. Typically this will be a value from the IANA Exporter Label Registry
(<https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#exporter-labels>). Alternatively labels
beginning with "EXPERIMENTAL" are permitted by the standard to be used without registration. TLSv1.3 imposes a
maximum label length of 249 bytes.
Note that this function is only defined for TLSv1.0 and above, and DTLSv1.0 and above. Attempting to use it in
SSLv3 will result in an error.
RETURN VALUES
SSL_export_keying_material() returns 0 or -1 on failure or 1 on success.
SSL_export_keying_material_early() returns 0 on failure or 1 on success.
SEE ALSO
ssl(7)
HISTORY
The SSL_export_keying_material_early() function was added in OpenSSL 1.1.1.
COPYRIGHT
Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the
License. You can obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.1.3 2023-09-19 SSL_EXPORT_KEYING_MATERIAL(3ossl)