Remove SSL_OP_NO_COMPRESSION from openssl initialization.
SSL_OP_NO_COMPRESSION was presumably added in an attempt to prevent information leakage in a manner similar to recent attacks on HTTPS. However, assuming that IRC is vulnerable to the same class of attacks is incorrect: the behavior of the IRC protocol (a single long-running connection) is not the same as that of HTTPS (multiple ephemeral connections). HTTPS's use of ephemeral connections means that certain assumptions can be made about the contents of the compression algorithm's dictionaries and the content exchanged between the client and server (e.g. the content being nearly the same for each connection), which is not true for IRC. Additionally, they rely on the attacker being able to coerce the client into creating many HTTPS connections (and resending some secret token belonging to the user, along with attacker-controlled data) each time, none of which is possible with IRC. Lastly, since compression is no longer performed, this option will result in leaking the lengths of messages transmitted to and from the client. This option does reduce CPU utilization on Charybdis servers but also increases bandwidth consumed.
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@ -313,9 +313,6 @@ rb_init_ssl(void)
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}
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/* Disable SSLv2, make the client use our settings */
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SSL_CTX_set_options(ssl_server_ctx, SSL_OP_NO_SSLv2 | SSL_OP_CIPHER_SERVER_PREFERENCE
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#ifdef SSL_OP_NO_COMPRESSION
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| SSL_OP_NO_COMPRESSION
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#endif
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#ifdef SSL_OP_SINGLE_DH_USE
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| SSL_OP_SINGLE_DH_USE
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#endif
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