1d5099dec6
Documentation fix ups as a result of feedback received. Reviewed-by: Tim Hudson <tjh@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org>
87 lines
2.9 KiB
Text
87 lines
2.9 KiB
Text
=pod
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=head1 NAME
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SSL_COMP_add_compression_method, SSL_COMP_free_compression_methods - handle SSL/TLS integrated compression methods
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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Deprecated:
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#if OPENSSL_API_COMPAT < 0x10100000L
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void SSL_COMP_free_compression_methods(void)
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#endif
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=head1 DESCRIPTION
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SSL_COMP_add_compression_method() adds the compression method B<cm> with
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the identifier B<id> to the list of available compression methods. This
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list is globally maintained for all SSL operations within this application.
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It cannot be set for specific SSL_CTX or SSL objects.
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In versions of OpenSSL prior to 1.1.0 SSL_COMP_free_compression_methods() freed
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the internal table of compression methods that were built internally, and
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possibly augmented by adding SSL_COMP_add_compression_method(). However this is
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now unncessary from version 1.1.0. No explicit initialisation or
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de-initialisation is necessary. See L<OPENSSL_init_crypto(3)> and
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L<OPENSSL_init_ssl(3)>. From OpenSSL 1.1.0 calling this function does nothing.
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=head1 NOTES
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The TLS standard (or SSLv3) allows the integration of compression methods
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into the communication. The TLS RFC does however not specify compression
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methods or their corresponding identifiers, so there is currently no compatible
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way to integrate compression with unknown peers. It is therefore currently not
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recommended to integrate compression into applications. Applications for
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non-public use may agree on certain compression methods. Using different
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compression methods with the same identifier will lead to connection failure.
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An OpenSSL client speaking a protocol that allows compression (SSLv3, TLSv1)
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will unconditionally send the list of all compression methods enabled with
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SSL_COMP_add_compression_method() to the server during the handshake.
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Unlike the mechanisms to set a cipher list, there is no method available to
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restrict the list of compression method on a per connection basis.
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An OpenSSL server will match the identifiers listed by a client against
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its own compression methods and will unconditionally activate compression
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when a matching identifier is found. There is no way to restrict the list
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of compression methods supported on a per connection basis.
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If enabled during compilation, the OpenSSL library will have the
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COMP_zlib() compression method available.
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=head1 WARNINGS
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Once the identities of the compression methods for the TLS protocol have
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been standardized, the compression API will most likely be changed. Using
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it in the current state is not recommended.
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=head1 RETURN VALUES
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SSL_COMP_add_compression_method() may return the following values:
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=over 4
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=item Z<>0
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The operation succeeded.
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=item Z<>1
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The operation failed. Check the error queue to find out the reason.
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=back
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=head1 SEE ALSO
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L<ssl(3)>
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=head1 HISTORY
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SSL_COMP_free_compression_methods() was deprecated in OpenSSL 1.1.0.
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=cut
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