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SSL_COMP_add_compression_method(3)	     OpenSSL	       SSL_COMP_add_compression_method(3)

NAME
       SSL_COMP_add_compression_method - handle SSL/TLS integrated compression methods

SYNOPSIS
	#include <openssl/ssl.h>

	int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);

DESCRIPTION
       SSL_COMP_add_compression_method() adds the compression method cm with the identifier id to
       the list of available compression methods. This list is globally maintained for all SSL
       operations within this application.  It cannot be set for specific SSL_CTX or SSL objects.

NOTES
       The TLS standard (or SSLv3) allows the integration of compression methods into the
       communication. The TLS RFC does however not specify compression methods or their
       corresponding identifiers, so there is currently no compatible way to integrate
       compression with unknown peers. It is therefore currently not recommended to integrate
       compression into applications. Applications for non-public use may agree on certain
       compression methods. Using different compression methods with the same identifier will
       lead to connection failure.

       An OpenSSL client speaking a protocol that allows compression (SSLv3, TLSv1) will
       unconditionally send the list of all compression methods enabled with
       SSL_COMP_add_compression_method() to the server during the handshake.  Unlike the
       mechanisms to set a cipher list, there is no method available to restrict the list of
       compression method on a per connection basis.

       An OpenSSL server will match the identifiers listed by a client against its own
       compression methods and will unconditionally activate compression when a matching
       identifier is found. There is no way to restrict the list of compression methods supported
       on a per connection basis.

       The OpenSSL library has the compression methods COMP_rle() and (when especially enabled
       during compilation) COMP_zlib() available.

WARNINGS
       Once the identities of the compression methods for the TLS protocol have been
       standardized, the compression API will most likely be changed. Using it in the current
       state is not recommended.

       It is also not recommended to use compression if data transfered contain untrusted parts
       that can be manipulated by an attacker as he could then get information about the
       encrypted data. See the CRIME attack. For that reason the default loading of the zlib
       compression method is disabled and enabled only if the environment variable
       OPENSSL_DEFAULT_ZLIB is present during the library initialization.

RETURN VALUES
       SSL_COMP_add_compression_method() may return the following values:

       0   The operation succeeded.

       1   The operation failed. Check the error queue to find out the reason.

SEE ALSO
       ssl(3)

1.0.1e					    2014-06-17	       SSL_COMP_add_compression_method(3)
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