mirror of
https://github.com/openssl/openssl.git
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151 lines
5.4 KiB
Plaintext
151 lines
5.4 KiB
Plaintext
=pod
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=head1 NAME
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SSL_CTX_set_mode, SSL_CTX_clear_mode, SSL_set_mode, SSL_clear_mode, SSL_CTX_get_mode, SSL_get_mode - manipulate SSL engine mode
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
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long SSL_CTX_clear_mode(SSL_CTX *ctx, long mode);
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long SSL_set_mode(SSL *ssl, long mode);
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long SSL_clear_mode(SSL *ssl, long mode);
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long SSL_CTX_get_mode(SSL_CTX *ctx);
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long SSL_get_mode(SSL *ssl);
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=head1 DESCRIPTION
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SSL_CTX_set_mode() adds the mode set via bit-mask in B<mode> to B<ctx>.
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Options already set before are not cleared.
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SSL_CTX_clear_mode() removes the mode set via bit-mask in B<mode> from B<ctx>.
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SSL_set_mode() adds the mode set via bit-mask in B<mode> to B<ssl>.
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Options already set before are not cleared.
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SSL_clear_mode() removes the mode set via bit-mask in B<mode> from B<ssl>.
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SSL_CTX_get_mode() returns the mode set for B<ctx>.
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SSL_get_mode() returns the mode set for B<ssl>.
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=head1 NOTES
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The following mode changes are available:
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=over 4
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=item SSL_MODE_ENABLE_PARTIAL_WRITE
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Allow SSL_write_ex(..., n, &r) to return with 0 < r < n (i.e. report success
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when just a single record has been written). This works in a similar way for
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SSL_write(). When not set (the default), SSL_write_ex() or SSL_write() will only
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report success once the complete chunk was written. Once SSL_write_ex() or
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SSL_write() returns successful, B<r> bytes have been written and the next call
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to SSL_write_ex() or SSL_write() must only send the n-r bytes left, imitating
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the behaviour of write().
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This mode cannot be enabled while in the middle of an incomplete write
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operation.
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=item SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
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Make it possible to retry SSL_write_ex() or SSL_write() with changed buffer
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location (the buffer contents must stay the same). This is not the default to
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avoid the misconception that nonblocking SSL_write() behaves like
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nonblocking write().
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=item SSL_MODE_AUTO_RETRY
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During normal operations, non-application data records might need to be sent or
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received that the application is not aware of.
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If a non-application data record was processed,
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L<SSL_read_ex(3)> and L<SSL_read(3)> can return with a failure and indicate the
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need to retry with B<SSL_ERROR_WANT_READ>.
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If such a non-application data record was processed, the flag
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B<SSL_MODE_AUTO_RETRY> causes it to try to process the next record instead of
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returning.
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In a nonblocking environment applications must be prepared to handle
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incomplete read/write operations.
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Setting B<SSL_MODE_AUTO_RETRY> for a nonblocking B<BIO> will process
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non-application data records until either no more data is available or
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an application data record has been processed.
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In a blocking environment, applications are not always prepared to
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deal with the functions returning intermediate reports such as retry
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requests, and setting the B<SSL_MODE_AUTO_RETRY> flag will cause the functions
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to only return after successfully processing an application data record or a
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failure.
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Turning off B<SSL_MODE_AUTO_RETRY> can be useful with blocking B<BIO>s in case
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they are used in combination with something like select() or poll().
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Otherwise the call to SSL_read() or SSL_read_ex() might hang when a
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non-application record was sent and no application data was sent.
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=item SSL_MODE_RELEASE_BUFFERS
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When we no longer need a read buffer or a write buffer for a given SSL,
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then release the memory we were using to hold it.
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Using this flag can
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save around 34k per idle SSL connection.
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This flag has no effect on SSL v2 connections, or on DTLS connections.
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=item SSL_MODE_SEND_FALLBACK_SCSV
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Send TLS_FALLBACK_SCSV in the ClientHello.
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To be set only by applications that reconnect with a downgraded protocol
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version; see draft-ietf-tls-downgrade-scsv-00 for details.
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DO NOT ENABLE THIS if your application attempts a normal handshake.
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Only use this in explicit fallback retries, following the guidance
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in draft-ietf-tls-downgrade-scsv-00.
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=item SSL_MODE_ASYNC
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Enable asynchronous processing. TLS I/O operations may indicate a retry with
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SSL_ERROR_WANT_ASYNC with this mode set if an asynchronous capable engine is
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used to perform cryptographic operations. See L<SSL_get_error(3)>.
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=item SSL_MODE_DTLS_SCTP_LABEL_LENGTH_BUG
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Older versions of OpenSSL had a bug in the computation of the label length
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used for computing the endpoint-pair shared secret. The bug was that the
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terminating zero was included in the length of the label. Setting this option
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enables this behaviour to allow interoperability with such broken
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implementations. Please note that setting this option breaks interoperability
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with correct implementations. This option only applies to DTLS over SCTP.
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=back
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All modes are off by default except for SSL_MODE_AUTO_RETRY which is on by
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default since 1.1.1.
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=head1 RETURN VALUES
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SSL_CTX_set_mode() and SSL_set_mode() return the new mode bit-mask
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after adding B<mode>.
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SSL_CTX_get_mode() and SSL_get_mode() return the current bit-mask.
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=head1 SEE ALSO
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L<ssl(7)>, L<SSL_read_ex(3)>, L<SSL_read(3)>, L<SSL_write_ex(3)> or
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L<SSL_write(3)>, L<SSL_get_error(3)>
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=head1 HISTORY
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SSL_MODE_ASYNC was added in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2001-2023 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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