1SSL_CTX_SET_RECORD_PADDING_CALLBACK(3O)penSSSSLL_CTX_SET_RECORD_PADDING_CALLBACK(3)
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NAME

6       SSL_CTX_set_record_padding_callback, SSL_set_record_padding_callback,
7       SSL_CTX_set_record_padding_callback_arg,
8       SSL_set_record_padding_callback_arg,
9       SSL_CTX_get_record_padding_callback_arg,
10       SSL_get_record_padding_callback_arg, SSL_CTX_set_block_padding,
11       SSL_set_block_padding - install callback to specify TLS 1.3 record
12       padding
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SYNOPSIS

15        #include <openssl/ssl.h>
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17        void SSL_CTX_set_record_padding_callback(SSL_CTX *ctx, size_t (*cb)(SSL *s, int type, size_t len, void *arg));
18        void SSL_set_record_padding_callback(SSL *ssl, size_t (*cb)(SSL *s, int type, size_t len, void *arg));
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20        void SSL_CTX_set_record_padding_callback_arg(SSL_CTX *ctx, void *arg);
21        void *SSL_CTX_get_record_padding_callback_arg(const SSL_CTX *ctx);
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23        void SSL_set_record_padding_callback_arg(SSL *ssl, void *arg);
24        void *SSL_get_record_padding_callback_arg(const SSL *ssl);
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26        int SSL_CTX_set_block_padding(SSL_CTX *ctx, size_t block_size);
27        int SSL_set_block_padding(SSL *ssl, size_t block_size);
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DESCRIPTION

30       SSL_CTX_set_record_padding_callback() or
31       SSL_set_record_padding_callback() can be used to assign a callback
32       function cb to specify the padding for TLS 1.3 records. The value set
33       in ctx is copied to a new SSL by SSL_new().
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35       SSL_CTX_set_record_padding_callback_arg() and
36       SSL_set_record_padding_callback_arg() assign a value arg that is passed
37       to the callback when it is invoked. The value set in ctx is copied to a
38       new SSL by SSL_new().
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40       SSL_CTX_get_record_padding_callback_arg() and
41       SSL_get_record_padding_callback_arg() retrieve the arg value that is
42       passed to the callback.
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44       SSL_CTX_set_block_padding() and SSL_set_block_padding() pads the record
45       to a multiple of the block_size. A block_size of 0 or 1 disables block
46       padding. The limit of block_size is SSL3_RT_MAX_PLAIN_LENGTH.
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48       The callback is invoked for every record before encryption.  The type
49       parameter is the TLS record type that is being processed; may be one of
50       SSL3_RT_APPLICATION_DATA, SSL3_RT_HANDSHAKE, or SSL3_RT_ALERT.  The len
51       parameter is the current plaintext length of the record before
52       encryption.  The arg parameter is the value set via
53       SSL_CTX_set_record_padding_callback_arg() or
54       SSL_set_record_padding_callback_arg().
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RETURN VALUES

57       The SSL_CTX_get_record_padding_callback_arg() and
58       SSL_get_record_padding_callback_arg() functions return the arg value
59       assigned in the corresponding set functions.
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61       The SSL_CTX_set_block_padding() and SSL_set_block_padding() functions
62       return 1 on success or 0 if block_size is too large.
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64       The cb returns the number of padding bytes to add to the record. A
65       return of 0 indicates no padding will be added. A return value that
66       causes the record to exceed the maximum record size
67       (SSL3_RT_MAX_PLAIN_LENGTH) will pad out to the maximum record size.
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NOTES

70       The default behavior is to add no padding to the record.
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72       A user-supplied padding callback function will override the behavior
73       set by SSL_set_block_padding() or SSL_CTX_set_block_padding(). Setting
74       the user-supplied callback to NULL will restore the configured block
75       padding behavior.
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77       These functions only apply to TLS 1.3 records being written.
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79       Padding bytes are not added in constant-time.
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SEE ALSO

82       ssl(7), SSL_new(3)
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HISTORY

85       The record padding API was added for TLS 1.3 support in OpenSSL 1.1.1.
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88       Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved.
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90       Licensed under the OpenSSL license (the "License").  You may not use
91       this file except in compliance with the License.  You can obtain a copy
92       in the file LICENSE in the source distribution or at
93       <https://www.openssl.org/source/license.html>.
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971.1.1i                            2021-07S-S2L2_CTX_SET_RECORD_PADDING_CALLBACK(3)
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