Information Technology Reference
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Fig. 1. The structure of finite state machine A HTTP , designed for the detection of network attacks
on Web-servers
During the analysis of HTTP-requests state machine A HTTP uses the following
auxiliary variables:
S methods - one-dimensional string array with the list of allowed HTTP-methods,
L URL - numeric variable, that specifies the maximum allowed length of the URL
(for example “www.mati.ru/scripts/example.exe” is an URL in the following
HTTP-request “http://www.mati.ru/scripts/example.exe”),
S URL - one-dimensional string array with list of resources, stored on Web-server
(this array can represent both static and dynamic Web-environment because of the
ability to use regular expressions),
L NQuery - numeric variable, that specifies the maximum allowed number of
parameters in a HTTP-query (for example “?var1=test1&var2=test2” is query in
the
following
request
“http://www.mati.ru/scripts/example.exe?var1=test1&
var2=test2”),
L VarLength - numeric variable, that specifies the maximum length of a variable name
being passed via a HTTP-query (for example “var1” and “var2” are variable names
in the following request “http://www.mati.ru/scripts/example.exe?var1=test1&
var2=test2”),
L ValLength - numeric variable, that specifies the maximum length of the data being
supplied for a specific variable (for example “test1” and “test2” are variable data
entries in the following request “http://www.mati.ru/scripts/example.exe?
var1=test1&var2=test2”),
L NHeaders - numeric variable, that specifies the maximum allowed number of
headers in HTTP-request,
S Versions - one-dimensional string array, that contains the list of HTTP protocol
versions, supported by the protected Web-server,
S Headers - one-dimensional string array with the list of allowed HTTP-headers,
Z - temporary string variable, which is used for the storage of HTTP-request
fragments,
i , j , k - temporary numeric variables, that are used as counters.
The variables Z , i , j and k are initialized automatically during the work of state
machine A HTTP , whereas all other variables should be initialized by the operator before
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