SSL_get_max_early_data,
SSL_CTX_get_max_early_data,
SSL_SESSION_get_max_early_data,
-SSL_write_early,
-SSL_write_early_finish,
-SSL_read_early,
+SSL_write_early_data,
+SSL_read_early_data,
SSL_get_early_data_status
- functions for sending and receiving early data
uint32_t SSL_get_max_early_data(const SSL_CTX *s);
uint32_t SSL_SESSION_get_max_early_data(const SSL_SESSION *s);
- int SSL_write_early(SSL *s, const void *buf, size_t num, size_t *written);
- int SSL_write_early_finish(SSL *s);
+ int SSL_write_early_data(SSL *s, const void *buf, size_t num, size_t *written);
- int SSL_read_early(SSL *s, void *buf, size_t num, size_t *readbytes);
+ int SSL_read_early_data(SSL *s, void *buf, size_t num, size_t *readbytes);
int SSL_get_early_data_status(const SSL *s);
=head1 DESCRIPTION
-These functions are used to send and recieve early data. Early data can be sent
-by the client immediately after its initial ClientHello without having to wait
-for the server to complete the handshake. Early data can only be sent if a
-session has previously been established with the server, and the server is known
-to support it.
+These functions are used to send and recieve early data where TLSv1.3 has been
+negotiated. Early data can be sent by the client immediately after its initial
+ClientHello without having to wait for the server to complete the handshake.
+Early data can only be sent if a session has previously been established with
+the server, and the server is known to support it. Additionally these functions
+can be used to send data from the server to the client when the client has not
+yet completed the authentication stage of the handshake.
Early data has weaker security properties than other data sent over an SSL/TLS
-connection. In particular the data is not forward secret and the server has no
-guarantees that the same early data was not replayed across multiple
+connection. In particular the data does not have forward secrecy and there are
+no guarantees that the same early data was not replayed across multiple
connections. For this reason extreme care should be exercised when using early
data.
-On the client side the function SSL_SESSION_get_max_early_data() can be used to
-determine whether a session established with a server can be used to send early
-data. If the session cannot be used then this function will return 0. Otherwise
-it will return the maximum number of early data bytes that can be sent.
-
-A client uses the function SSL_write_early() to send early data. This function
-works in the same way as the L<SSL_write_ex(3)> function, but with a few
-differences. Refer to the L<SSL_write_ex(3)> documentation for
-information on how to write bytes to the underlying connection, and how to
-handle any errors that may arise. This page will detail the differences between
-SSL_write_early() and L<SSL_write_ex(3)>.
-
-SSL_write_early() must be the first IO function called on a new connection, i.e.
-it must occur before any calls to L<SSL_write_ex(3)>, L<SSL_read_ex(3)>,
-L<SSL_connect(3)>, L<SSL_do_handshake(3)> or other similar functions. It may be
-called multiple times to stream data to the server, but the total number of
-bytes written must not exceed the value returned from
-SSL_SESSION_get_max_early_data().
-
-Once finished writing early data you must then call SSL_write_early_finish().
-This sends a message to the server signalling the end of early data.
-
-If either SSL_write_early() or SSL_write_early_finish() fail you should call
-L<SSL_get_error(3)> to determine the correct course of action, as for
+When a server receives early data it may opt to immediately respond by sending
+application data back to the client. Data sent by the server at this stage is
+done before the full handshake has been completed. Specifically the client's
+authentication messages have not yet been received, i.e. the client is
+unauthenticated at this point and care should be taken when using this
+capability.
+
+A server or client can determine whether the full handshake has been completed
+or not by calling L<SSL_is_init_finished(3)>.
+
+On the client side, the function SSL_SESSION_get_max_early_data() can be used to
+determine if a session established with a server can be used to send early data.
+If the session cannot be used then this function will return 0. Otherwise it
+will return the maximum number of early data bytes that can be sent.
+
+A client uses the function SSL_write_early_data() to send early data. This
+function is similar to the L<SSL_write_ex(3)> function, but with the following
+differences. See L<SSL_write_ex(3)> for information on how to write bytes to
+the underlying connection, and how to handle any errors that may arise. This
+page describes the differences between SSL_write_early_data() and
L<SSL_write_ex(3)>.
-Following an SSL_write_early_finish() call the connection to the server still
-needs to be completed. Complete the connection by calling a function such as
-L<SSL_connect(3)> or L<SSL_do_handshake(3)>. Alternatively you can call a
-"normal" read/write function such as L<SSL_read_ex(3)> or L<SSL_write_ex(3)>,
-which will transparently complete the connection and read/write the requested
-data.
-
-Only clients may call SSL_write_early() or SSL_write_early_finish().
+When called by a client, SSL_write_early_data() must be the first IO function
+called on a new connection, i.e. it must occur before any calls to
+L<SSL_write_ex(3)>, L<SSL_read_ex(3)>, L<SSL_connect(3)>, L<SSL_do_handshake(3)>
+or other similar functions. It may be called multiple times to stream data to
+the server, but the total number of bytes written must not exceed the value
+returned from SSL_SESSION_get_max_early_data(). Once the initial
+SSL_write_early_data() call has completed successfully the client may interleave
+calls to L<SSL_read_ex(3)> and L<SSL_read(3)> with calls to
+SSL_write_early_data() as required.
+
+If SSL_write_early_data() fails you should call L<SSL_get_error(3)> to determine
+the correct course of action, as for L<SSL_write_ex(3)>.
+
+When the client no longer wishes to send any more early data then it should
+complete the handshake by calling a function such as L<SSL_connect(3)> or
+L<SSL_do_handshake(3)>. Alternatively you can call a standard write function
+such as L<SSL_write_ex(3)>, which will transparently complete the connection and
+write the requested data.
A server may choose to ignore early data that has been sent to it. Once the
connection has been completed you can determine whether the server accepted or
was rejected or SSL_EARLY_DATA_NOT_SENT if no early data was sent. This function
may be called by either the client or the server.
-A server uses the SSL_read_early() function to receive early data on a
-connection. As for SSL_write_early() this must be the first IO function called
-on a connection, i.e. it must occur before any calls to L<SSL_write_ex(3)>,
-L<SSL_read_ex(3)>, L<SSL_accept(3)>, L<SSL_do_handshake(3)>, or other similar
-functions.
+A server uses the SSL_read_early_data() function to receive early data on a
+connection. As for SSL_write_early_data() this must be the first IO function
+called on a connection, i.e. it must occur before any calls to
+L<SSL_write_ex(3)>, L<SSL_read_ex(3)>, L<SSL_accept(3)>, L<SSL_do_handshake(3)>,
+or other similar functions.
-SSL_read_early() works in the same way as L<SSL_read_ex(3)> except for the
-differences noted here. Refer to the L<SSL_read_ex(3)> documentation for full
-details.
+SSL_read_early_data() is similar to L<SSL_read_ex(3)> with the following
+differences. Refer to L<SSL_read_ex(3)> for full details.
-SSL_read_early() may return 3 possible values:
+SSL_read_early_data() may return 3 possible values:
=over 4
-=item SSL_READ_EARLY_ERROR
+=item SSL_READ_EARLY_DATA_ERROR
This indicates an IO or some other error occured. This should be treated in the
same way as a 0 return value from L<SSL_read_ex(3)>.
-=item SSL_READ_EARLY_SUCCESS
+=item SSL_READ_EARLY_DATA_SUCCESS
This indicates that early data was successfully read. This should be treated in
the same way as a 1 return value from L<SSL_read_ex(3)>. You should continue to
-call SSL_read_early() to read more data.
+call SSL_read_early_data() to read more data.
-=item SSL_READ_EARLY_FINISH
+=item SSL_READ_EARLY_DATA_FINISH
This indicates that no more early data can be read. It may be returned on the
-first call to SSL_read_early() if the client has not sent any early data, or
-if the early data was rejected.
+first call to SSL_read_early_data() if the client has not sent any early data,
+or if the early data was rejected.
=back
-Once SSL_read_early() returns SSL_READ_EARLY_FINISH the connection to the client
+Once the initial SSL_read_early_data() call has completed successfully (i.e. it
+has returned SSL_READ_EARLY_DATA_SUCCESS or SSL_READ_EARLY_DATA_FINISH) then the
+server may choose to write data immediately to the unauthenticated client using
+SSL_write_early_data(). If SSL_read_early_data() returned
+SSL_READ_EARLY_DATA_FINISH then in some situations (e.g. if the client only
+supports TLSv1.2) the handshake may have already been completed and calls
+to SSL_write_early_data() are not allowed. Call L<SSL_is_init_finished(3)> to
+determine whether the handshake has completed or not. If the handshake is still
+in progress then the server may interleave calls to SSL_write_early_data() with
+calls to SSL_read_early_data() as required.
+
+Servers must not call L<SSL_read_ex(3)>, L<SSL_read(3)>, L<SSL_write_ex(3)> or
+L<SSL_write(3)> until SSL_read_early_data() has returned with
+SSL_READ_EARLY_DATA_FINISH. Once it has done so the connection to the client
still needs to be completed. Complete the connection by calling a function such
as L<SSL_accept(3)> or L<SSL_do_handshake(3)>. Alternatively you can call a
-"normal" read/write function such as L<SSL_read_ex(3)> or L<SSL_write_ex(3)>,
-which will transparently complete the connection and read/write the requested
-data. Note that it is an error to attempt to complete the connection before
-SSL_read_early() has returned SSL_READ_EARLY_FINISH.
+standard read function such as L<SSL_read_ex(3)>, which will transparently
+complete the connection and read the requested data. Note that it is an error to
+attempt to complete the connection before SSL_read_early_data() has returned
+SSL_READ_EARLY_DATA_FINISH.
+
+Only servers may call SSL_read_early_data().
-Only servers may call SSL_read_early().
+Calls to SSL_read_early_data() may, in certain circumstances, complete the
+connection immediately without further need to call a function such as
+L<SSL_accept(3)>. This can happen if the client is using a protocol version less
+than TLSv1.3. Applications can test for this by calling
+L<SSL_is_init_finished(3)>. Alternatively, applications may choose to call
+L<SSL_accept(3)> anway. Such a call will successfully return immediately with no
+further action taken.
When a session is created between a server and a client the server will specify
the maximum amount of any early data that it will accept on any future
=head1 RETURN VALUES
-SSL_write_early() and SSL_write_early_finish() return 1 for success or 0 for
-failure. In the event of a failure call L<SSL_get_error(3)> to determine the
-correct course of action.
+SSL_write_early_data() returns 1 for success or 0 for failure. In the event of a
+failure call L<SSL_get_error(3)> to determine the correct course of action.
-SSL_read_early() returns SSL_READ_EARLY_ERROR for failure,
-SSL_READ_EARLY_SUCCESS for success with more data to read and
-SSL_READ_EARLY_FINISH for no more to data be read. In the event of a failure
-call L<SSL_get_error(3)> to determine the correct course of action.
+SSL_read_early_data() returns SSL_READ_EARLY_DATA_ERROR for failure,
+SSL_READ_EARLY_DATA_SUCCESS for success with more data to read and
+SSL_READ_EARLY_DATA_FINISH for success with no more to data be read. In the
+event of a failure call L<SSL_get_error(3)> to determine the correct course of
+action.
SSL_get_max_early_data(), SSL_CTX_get_max_early_data() and
SSL_SESSION_get_max_early_data() return the maximum number of early data bytes
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