Edit File: SSL_set_block_padding.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "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 .SH "SYNOPSIS" .IX 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)); \& 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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBSSL_CTX_set_record_padding_callback()\fR or \fBSSL_set_record_padding_callback()\fR can be used to assign a callback function \fIcb\fR to specify the padding for \s-1TLS 1.3\s0 records. The value set in \fBctx\fR is copied to a new \s-1SSL\s0 by \fBSSL_new()\fR. .PP \&\fBSSL_CTX_set_record_padding_callback_arg()\fR and \fBSSL_set_record_padding_callback_arg()\fR assign a value \fBarg\fR that is passed to the callback when it is invoked. The value set in \fBctx\fR is copied to a new \s-1SSL\s0 by \fBSSL_new()\fR. .PP \&\fBSSL_CTX_get_record_padding_callback_arg()\fR and \fBSSL_get_record_padding_callback_arg()\fR retrieve the \fBarg\fR value that is passed to the callback. .PP \&\fBSSL_CTX_set_block_padding()\fR and \fBSSL_set_block_padding()\fR pads the record to a multiple of the \fBblock_size\fR. A \fBblock_size\fR of 0 or 1 disables block padding. The limit of \&\fBblock_size\fR is \s-1SSL3_RT_MAX_PLAIN_LENGTH.\s0 .PP The callback is invoked for every record before encryption. The \fBtype\fR 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 \fBlen\fR parameter is the current plaintext length of the record before encryption. The \fBarg\fR parameter is the value set via \fBSSL_CTX_set_record_padding_callback_arg()\fR or \fBSSL_set_record_padding_callback_arg()\fR. .SH "RETURN VALUES" .IX Header "RETURN VALUES" The \fBSSL_CTX_get_record_padding_callback_arg()\fR and \fBSSL_get_record_padding_callback_arg()\fR functions return the \fBarg\fR value assigned in the corresponding set functions. .PP The \fBSSL_CTX_set_block_padding()\fR and \fBSSL_set_block_padding()\fR functions return 1 on success or 0 if \fBblock_size\fR is too large. .PP The \fBcb\fR 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. .SH "NOTES" .IX Header "NOTES" The default behavior is to add no padding to the record. .PP A user-supplied padding callback function will override the behavior set by \&\fBSSL_set_block_padding()\fR or \fBSSL_CTX_set_block_padding()\fR. Setting the user-supplied callback to \s-1NULL\s0 will restore the configured block padding behavior. .PP These functions only apply to \s-1TLS 1.3\s0 records being written. .PP Padding bytes are not added in constant-time. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBssl\fR\|(7), \fBSSL_new\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" The record padding \s-1API\s0 was added for \s-1TLS 1.3\s0 support in OpenSSL 1.1.1. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2017\-2019 The OpenSSL Project Authors. All Rights Reserved. .PP 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>.