focal (3) SSL_set_block_padding.3ssl.gz

Provided by: libssl-doc_1.1.1f-1ubuntu2.24_all bug

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


SYNOPSIS
        #include <openssl/ssl.h>

        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(const SSL_CTX *ctx);

        void SSL_set_record_padding_callback_arg(SSL *ssl, void *arg);
        void *SSL_get_record_padding_callback_arg(const 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);


DESCRIPTION
       SSL_CTX_set_record_padding_callback() or SSL_set_record_padding_callback() can be used to assign a
       callback function cb to specify the padding for TLS 1.3 records. The value set in ctx 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 arg
       that is passed to the callback when it is invoked. The value set in ctx 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 arg
       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 block_size.
       A block_size of 0 or 1 disables block padding. The limit of block_size is SSL3_RT_MAX_PLAIN_LENGTH.

       The callback is invoked for every record before encryption.  The type 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 len parameter is the current plaintext length of the record before encryption.  The arg parameter is
       the value set via SSL_CTX_set_record_padding_callback_arg() or SSL_set_record_padding_callback_arg().


RETURN VALUES
       The SSL_CTX_get_record_padding_callback_arg() and SSL_get_record_padding_callback_arg() functions return
       the arg value assigned in the corresponding set functions.

       The SSL_CTX_set_block_padding() and SSL_set_block_padding() functions return 1 on success or 0 if
       block_size is too large.

       The cb 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.


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.


SEE ALSO
       ssl(7), SSL_new(3)


HISTORY
       The record padding API was added for TLS 1.3 support in OpenSSL 1.1.1.


       Copyright 2017-2019 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
       <https://www.openssl.org/source/license.html>.