trusty (3) SSL_COMP_add_compression_method.3ssl.gz

Provided by: libssl-doc_1.0.1f-1ubuntu2.27_all bug

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.


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)