=pod =head1 NAME SSL_CTX_set_record_padding_callback, SSL_set_record_padding_callback, SSL_CTX_set_record_padding_callback_arg, SSL_set_record_padding_callback_arg, SSL_CTX_get_record_padding_callback_arg, SSL_get_record_padding_callback_arg, SSL_CTX_set_block_padding, SSL_set_block_padding - install callback to specify TLS 1.3 record padding =head1 SYNOPSIS #include void SSL_CTX_set_record_padding_callback(SSL_CTX *ctx, size_t (*cb)(SSL *s, int type, size_t len, void *arg)); void SSL_set_record_padding_callback(SSL *ssl, size_t (*cb)(SSL *s, int type, size_t len, void *arg)); void SSL_CTX_set_record_padding_callback_arg(SSL_CTX *ctx, void *arg); void *SSL_CTX_get_record_padding_callback_arg(SSL_CTX *ctx); void SSL_set_record_padding_callback_arg(SSL *ssl, void *arg); void *SSL_get_record_padding_callback_arg(SSL *ssl); int SSL_CTX_set_block_padding(SSL_CTX *ctx, size_t block_size); int SSL_set_block_padding(SSL *ssl, size_t block_size); =head1 DESCRIPTION SSL_CTX_set_record_padding_callback() or SSL_set_record_padding_callback() can be used to assign a callback function I to specify the padding for TLS 1.3 records. The value set in B is copied to a new SSL by SSL_new(). SSL_CTX_set_record_padding_callback_arg() and SSL_set_record_padding_callback_arg() assign a value B that is passed to the callback when it is invoked. The value set in B is copied to a new SSL by SSL_new(). SSL_CTX_get_record_padding_callback_arg() and SSL_get_record_padding_callback_arg() retrieve the B value that is passed to the callback. SSL_CTX_set_block_padding() and SSL_set_block_padding() pads the record to a multiple of the B. A B of 0 or 1 disables block padding. The limit of B is SSL3_RT_MAX_PLAIN_LENGTH. The callback is invoked for every record before encryption. The B parameter is the TLS record type that is being processed; may be one of SSL3_RT_APPLICATION_DATA, SSL3_RT_HANDSHAKE, or SSL3_RT_ALERT. The B parameter is the current plaintext length of the record before encryption. The B parameter is the value set via SSL_CTX_set_record_padding_callback_arg() or SSL_set_record_padding_callback_arg(). =head1 RETURN VALUES The SSL_CTX_get_record_padding_callback_arg() and SSL_get_record_padding_callback_arg() functions return the B value assignd in the corresponding set functions. The SSL_CTX_set_block_padding() and SSL_set_block_padding() functions return 1 on success or 0 if B is too large. The B returns the number of padding bytes to add to the record. A return of 0 indicates no padding will be added. A return value that causes the record to exceed the maximum record size (SSL3_RT_MAX_PLAIN_LENGTH) will pad out to the maximum record size. =head1 NOTES The default behavior is to add no padding to the record. A user-supplied padding callback function will override the behavior set by SSL_set_block_padding() or SSL_CTX_set_block_padding(). Setting the user-supplied callback to NULL will restore the configured block padding behavior. These functions only apply to TLS 1.3 records being written. Padding bytes are not added in constant-time. =head1 SEE ALSO L, L =head1 HISTORY The record padding API was added for TLS 1.3 support in OpenSSL 1.1.1. =head1 COPYRIGHT Copyright 2017 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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. =cut