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 CCOOMMPP__rrllee(()) and (when especially enabled during compilation) CCOOMMPP__zzlliibb(()) 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)

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