The site could generate fake address once in a while so even offline you are far from being protected. This would be hard to detect.
So my question is :
is there a simple site, eventually documented, so that one could look through the source code without much hassle and be sure that the program does what it is supposed to? Maybe a over simplified bitaddress ...
How is that even possible, especially offline? I used it offline for long and never encountered a fake address!
Regarding your Q, u may try
https://coinb.in.