SSL_COMP_ADD_COMPRESSION_METHOpeSnSSL_LCOMP_ADD_COMPRESSION_METHOD(3)
SSL_COMP_add_compression_method - handle SSL/TLS integrated
compression methods
#include <openssl/ssl.h>
int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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.
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 correspond-
ing 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 compres-
sion (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 uncondi-
tionally 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.
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.
MirBSD #10-current 2014-11-26 1
SSL_COMP_ADD_COMPRESSION_METHOpeSnSSL_LCOMP_ADD_COMPRESSION_METHOD(3)
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.
ssl(3)
MirBSD #10-current 2014-11-26 2