=pod

=head1 NAME

SSL_CTX_set_stateless_cookie_generate_cb,
SSL_CTX_set_stateless_cookie_verify_cb
- Callback functions for stateless TLS1.3 cookies

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 void SSL_CTX_set_stateless_cookie_generate_cb(
     SSL_CTX *ctx,
     int (*gen_stateless_cookie_cb) (SSL *ssl,
                                     unsigned char *cookie,
                                     size_t *cookie_len));
 void SSL_CTX_set_stateless_cookie_verify_cb(
     SSL_CTX *ctx,
     int (*verify_stateless_cookie_cb) (SSL *ssl,
                                        const unsigned char *cookie,
                                        size_t cookie_len));

=head1 DESCRIPTION

SSL_CTX_set_cookie_generate_cb() sets the callback used by L<SSL_stateless(3)>
to generate the application-controlled portion of the cookie provided to clients
in the HelloRetryRequest transmitted as a response to a ClientHello with a
missing or invalid cookie. gen_stateless_cookie_cb() must write at most
SSL_COOKIE_LENGTH bytes into B<cookie>, and must write the number of bytes
written to B<cookie_len>. If a cookie cannot be generated, a zero return value
can be used to abort the handshake.

SSL_CTX_set_cookie_verify_cb() sets the callback used by L<SSL_stateless(3)> to
determine whether the application-controlled portion of a ClientHello cookie is
valid. A nonzero return value from app_verify_cookie_cb() communicates that the
cookie is valid. The integrity of the entire cookie, including the
application-controlled portion, is automatically verified by HMAC before
verify_stateless_cookie_cb() is called.

=head1 RETURN VALUES

Neither function returns a value.

=head1 SEE ALSO

L<SSL_stateless(3)>

=head1 COPYRIGHT

Copyright 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
L<https://www.openssl.org/source/license.html>.

=cut
