Digital Signature - smart card

in internet there are many services that require a digital signature with a smart card.

I would like to know how it works... I can see that in eBay sell smart card with reader/writer for low money, but those companies that need Digital Signatures offer the same thing for much more money.

Is it the same stuff? If I buy one kit on eBay for about 20/30$, than I can pay taxes online and certify my Outlook emails?
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ParanormasticConnect With a Mentor Cryptographic EngineerCommented:
Yes and no.

Physically speaking - yes, its pretty much the same stuff.  Same standards for smartcards, same standards for smartcard readers.  There's different brands, of course, so the software may have extra features or whatever, but deep down, they are the same thing.

However...  the certificate you get issued from eBay isn't going to help you send in your taxes.  The certificates can be used for different things - like a client certificate that allows you access to a secured part of their site (instead of using a username/password you use the certficate), or you could use it to digitally sign a file as a legal signature.  

You could use the same reader, but you would need at least different certificates - technically you could fit a few dozen certs on a single smartcard.  However, many of these companies probably would not allow you to enroll your own card for security / validation reasons, so most likely they will need to send you their own card.

With multiple cards you may need to install extra software to recognize the "ATR" (answer to reset) of that card when it is inserted so the middleware knows how to talk to it, and some may be proprietary on top of that, which can get messy.

You can purchase your own certificate that you could use for more general usage from companies like Verisign and Comodo where you send them certain information (like a copy of your drivers license, etc.) to validate that you are in fact yourself.  Then they issue you your own personal digital signature certificate that should be kept on a smartcard or smart USB token for your own protection (this is now equal to your signature!).  This would be more likely acceptable for signing legal documents, emails, and maybe even your taxes - there may be stipulations for using it as such, so if you really want to do that then you might want to call up a lawyer referral service and ask them for the name of an computer security lawyer so they can explain what it is in your location.

Note that the free ID certs from many of the cert vendors are not legally recognized.  They are just fine if you just want them for your own use, but for legal purposes they need to validate information which means they need a person to do something, so it is going to cost a little bit of money (they're pretty cheap tho).

20-30 bucks for a smartcard isn't too bad - this is pretty typical pricing.
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