Subject: [Cfrg] How about a server-side message with NO HMAC?

From: ZhangYuan <[email-masked]>
Date: Sat, 3 May 2008 03:35:19 +0000

How about a server-side message with NO HMAC?
 
I have just adopted a secure protocol for a distributed multi-player game from 
TLS/SSl,in which 1000+ players act in the same world. The Question is about 
the Hashed-MAC field in its message format.
 
The protocol works much like SSL/TLS. Firstly "Hello", secondly "Shake-Hand" 
and "RSA Public Key",then "Pre-Master Secret" and "Cipher Algorithm Changed",
at last comes the "Encrypted Game Msg". 
 
The Format of "Encrypted Game Msg" includes [1]Length[2]Encrypted content[3]Encrypted Hashed-MAC[4]Encrypted Padding etc.The protocol is symmetric:both client and server will generate and send Hashed-MAC in 16 bytes.
 
Yet, I really suspect if a server MAC is necessary in a game context. Because there are many cracked clients or faked network message from the client to cheat. Instead, It is difficult to modify or crack the network message of a server serving for 1000+ connections at once. Moreover, to modify such an output of server will not affectthe game logic running inside servers. At most, such a modification or forgery will cause some clients to crash.
 
So, my question is: What security vulnerabilities will happen if we omitted the HMAC of server? Is that affordable 
in a Multi-Player Online Game? The saving of communication bytes and HMAC computation really tempts me :-P
 
Would you please give some hints about the question? Thanks in advance:-) 
_________________________________________________________________
MSN 中文网，最新时尚生活资讯，白领聚集门户。
http://cn.msn.com

_______________________________________________
Cfrg mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/cfrg