About external.ssf

[Biswatosh]

Hi
 In the function mech_permitted() in the file server.c
, there are the following lines:
*********************************************
/*
 * The rule is:
 * IF mech strength + external strength < min ssf THEN
FAIL
 * We also have to look at the security properties and
make sure
 * that this mechanism has everything we want
 */

if (conn->props.min_ssf < conn->external.ssf) {
        minssf = 0;
    } else {
        minssf = conn->props.min_ssf -
conn->external.ssf;
    }
***************************************************



Now,I am not understanding the requirement. Why is 
if (conn->props.min_ssf < conn->external.ssf)
condition checked in all cases? Pls correct me in my
understanding. Is it not that only when the mechanism
is EXTERNAL, that min.ssf should be > external.ssf?
Otherwise,if the mechanism is not EXTERNAL, what is
the role of external.ssf? 
And then, why if  conn->props.min_ssf <
conn->external.ssf, we are making minssf =0 else =
min_ssf - external.ssf?

Thanks
Biswatosh



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