SSL_COMP_add_compression_method - handle SSL/TLS integrated
int SSL_COMP_add_compression_method(int id, COMP_METHOD
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 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
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_compres-
sion_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)
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
SSL_COMP_add_compression_method() may return the following
0 The operation succeeded.
1 The operation failed. Check the error queue to find
out the reason.
OpenBSD 3.6 2004-04-08 2 [ Back ]