How can I lookup the registering info of an ISSN number?

While applying for an ISSN, applicants are asked to provide publisher name, country/city, contact info and editor name. How/where can I look up an ISSN number to get these info?

Of course for a single ISSN number, I can google, find the journal site and contact them via the website. But I am doing a research on a big number of ISSNs.

Moreover, how can I be sure it is not a fake number?!! Anyone can comeup with an 8 digit number, and call it an ISSN! IS there a main ISSN portal/service, where I can lookup ISSN numbers?

thanks