1SSL_COMP_add_compression_method(3)  OpenSSL SSL_COMP_add_compression_method(3)
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NAME

6       SSL_COMP_add_compression_method - handle SSL/TLS integrated compression
7       methods
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SYNOPSIS

10        #include <openssl/ssl.h>
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12        int SSL_COMP_add_compression_method(int id, COMP_METHOD *cm);
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DESCRIPTION

15       SSL_COMP_add_compression_method() adds the compression method cm with
16       the identifier id to the list of available compression methods. This
17       list is globally maintained for all SSL operations within this applica‐
18       tion.  It cannot be set for specific SSL_CTX or SSL objects.
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NOTES

21       The TLS standard (or SSLv3) allows the integration of compression meth‐
22       ods into the communication. The TLS RFC does however not specify com‐
23       pression methods or their corresponding identifiers, so there is cur‐
24       rently no compatible way to integrate compression with unknown peers.
25       It is therefore currently not recommended to integrate compression into
26       applications. Applications for non-public use may agree on certain com‐
27       pression methods. Using different compression methods with the same
28       identifier will lead to connection failure.
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30       An OpenSSL client speaking a protocol that allows compression (SSLv3,
31       TLSv1) will unconditionally send the list of all compression methods
32       enabled with SSL_COMP_add_compression_method() to the server during the
33       handshake.  Unlike the mechanisms to set a cipher list, there is no
34       method available to restrict the list of compression method on a per
35       connection basis.
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37       An OpenSSL server will match the identifiers listed by a client against
38       its own compression methods and will unconditionally activate compres‐
39       sion when a matching identifier is found. There is no way to restrict
40       the list of compression methods supported on a per connection basis.
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42       The OpenSSL library has the compression methods COMP_rle() and (when
43       especially enabled during compilation) COMP_zlib() available.
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WARNINGS

46       Once the identities of the compression methods for the TLS protocol
47       have been standardized, the compression API will most likely be
48       changed. Using it in the current state is not recommended.
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RETURN VALUES

51       SSL_COMP_add_compression_method() may return the following values:
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53       0   The operation succeeded.
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55       1   The operation failed. Check the error queue to find out the reason.
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SEE ALSO

58       ssl(3)
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620.9.8b                            2003-11-29SSL_COMP_add_compression_method(3)
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