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Updates to the early data documentation

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Following on from the latest API changes.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2737)
This commit is contained in:
Matt Caswell 2017-02-28 00:40:24 +00:00
parent ade1e88806
commit ef466accdc
1 changed files with 45 additions and 26 deletions
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71
doc/man3/SSL_read_early.pod
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@ -8,7 +8,6 @@ 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_get_early_data_status
- functions for sending and receiving early data
@ -24,7 +23,6 @@ SSL_get_early_data_status
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_read_early(SSL *s, void *buf, size_t num, size_t *readbytes);
@ -44,6 +42,19 @@ guarantees that the same early data was not replayed across multiple
connections. For this reason extreme care should be exercised when using early
data.
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.
A server or client can determine whether the full handshake has been completed
or not by calling L<SSL_is_init_finished(3)>.
[[TODO(TLS1.3): The server uses SSL_write_ex()/SSL_write() to send data to an
unauthenticated client. Should we create a separate function for this to avoid
accidents??]]
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
@ -61,23 +72,20 @@ 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().
SSL_SESSION_get_max_early_data(). Once the initial SSL_write_early() 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() as required.
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 SSL_write_early() fails you should call L<SSL_get_error(3)> to determine the
correct course of action, as for L<SSL_write_ex(3)>.
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
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.
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().
Only clients may call SSL_write_early().
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
@ -119,16 +127,28 @@ if the early data was rejected.
=back
Once SSL_read_early() returns SSL_READ_EARLY_FINISH 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.
Once the initial SSL_write_early() call has completed successfully the client
may interleave calls to L<SSL_write_ex(3)> and L<SSL_write(3)> with calls to
SSL_read_early() as required. As noted above data sent via L<SSL_write_ex(3)> or
L<SSL_write(3)> in this way is sent to an unauthenticated client.
Servers must not call L<SSL_read_ex(3)> or L<SSL_read(3)> until SSL_read_early()
has returned with SSL_READ_EARLY_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 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() has
returned SSL_READ_EARLY_FINISH.
Only servers may call SSL_read_early().
Calls to SSL_read_early() may, in certain circumstances, complete the connection
immediately without further need to call a function such as L<SSL_accept(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
connection attempt. By default this is approximately 16k. A server may override
@ -144,9 +164,8 @@ with then the lower of the two values will apply.
=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() 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