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)