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SSL_COMP_add_compression_method(3)  OpenSSL SSL_COMP_add_compression_method(3)

NAME
       SSL_COMP_add_compression_method, SSL_COMP_free_compression_methods -
       handle SSL/TLS integrated compression methods
SYNOPSIS
        #include <openssl/ssl.h>
        int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
        +void SSL_COMP_free_compression_methods(void);
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.
       SSL_COMP_free_compression_methods() frees the internal table of
       compression methods that were built internally, and possibly augmented
       by adding SSL_COMP_add_compression_method().
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.
       If enabled during compilation, the OpenSSL library will have the
       COMP_zlib() compression method 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)

1.0.2k                            2023-11-13SSL_COMP_add_compression_method(3)