Updated: 2021/Apr/14


SSL_CTX_set_record_padding_callback(3)                                 OpenSSL



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

LIBRARY
       libcrypto, -lcrypto

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
       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>.



1.1.1i                            2019-03-12
                                        SSL_CTX_set_record_padding_callback(3)