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Title "SSL_CTX_SET_RECORD_PADDING_CALLBACK 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
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 Header "SYNOPSIS" .Vb 1 #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)); int 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); .Ve Header "DESCRIPTION" \fBSSL_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 \s-1TLS 1.3\s0 records. The value set in ctx is copied to a new \s-1SSL\s0 by SSL_new(). Kernel \s-1TLS\s0 is not possible if the record padding callback is set, and the callback function cannot be set if Kernel \s-1TLS\s0 is already configured for the current \s-1SSL\s0 object.

\fBSSL_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 \s-1SSL\s0 by SSL_new().

\fBSSL_CTX_get_record_padding_callback_arg() and SSL_get_record_padding_callback_arg() retrieve the arg value that is passed to the callback.

\fBSSL_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 \fBblock_size is \s-1SSL3_RT_MAX_PLAIN_LENGTH.\s0

The callback is invoked for every record before encryption. The type parameter is the \s-1TLS\s0 record type that is being processed; may be one of \s-1SSL3_RT_APPLICATION_DATA, SSL3_RT_HANDSHAKE,\s0 or \s-1SSL3_RT_ALERT.\s0 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().

Header "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 (\s-1SSL3_RT_MAX_PLAIN_LENGTH\s0) will pad out to the maximum record size.

The SSL_CTX_get_record_padding_callback_arg() function returns 1 on success or 0 if the callback function is not set because Kernel \s-1TLS\s0 is configured for the \s-1SSL\s0 object.

Header "NOTES" The default behavior is to add no padding to the record.

A user-supplied padding callback function will override the behavior set by \fBSSL_set_block_padding() or SSL_CTX_set_block_padding(). Setting the user-supplied callback to \s-1NULL\s0 will restore the configured block padding behavior.

These functions only apply to \s-1TLS 1.3\s0 records being written.

Padding bytes are not added in constant-time.

Header "SEE ALSO" \fBssl\|(7), SSL_new\|(3) Header "HISTORY" The record padding \s-1API\s0 was added for \s-1TLS 1.3\s0 support in OpenSSL 1.1.1.

The return type of SSL_CTX_set_record_padding_callback() function was changed to int in OpenSSL 3.0.

Header "COPYRIGHT" Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.