Smart Card
Smart Cards were used on the first-generation WebTV/MSN TV service to take the user to a site, set up ISP options, etc. They were rarely utilized, and removed from MSNTV 2 later.
Overview
When a Smart Card is inserted into the WebTV/MSN TV receiver, it will show a message on the screen with the Smart Card name and a progress bar. In the background, it's contacting the URL from the wtv-smartcard-inserted-url header, which is usually wtv-smartcard:/insert. The box will POST the raw data read from the card to the URL (sometimes the box will base64 encode the data, but the reasoning for this is unknown), which will then decode it and return either a wtv-smartcard page with an error/confirmation page, or a redirect to somewhere else. In some cases, the box will send an error header (e.g: "error="-68") if something goes wrong.
Structure
For now, we'll be focusing on Go To cards, as that's what we have info on.
This is the data stored on a Go To Smart Card:
2Gÿt�Sony Value G�i999999
We can break this data up into several parts to get all the data that the server decodes.
The first byte is the Smart Card generation, which appears to always be 2 except for a special type of Go To card, which uses generation 1. "Generation" is assumed to refer to the data format for the card, not a different version of Smart Cards themselves.
The second byte is the Smart Card type, which is (G)o To in this case. Other observed values include (O)penISP and (A)ffinity.
ÿ appears to be a separator, which is followed by t�, which defines the start of the Smart Card title.
G�i appears to stand for "Go To ID", which is the ID for the Go To card. The ID has a corresponding URL that is stored on the server. If the ID is unknown, then a message about the Smart Card being expired or not yet active is sent to the client. The reasoning for this approach appears to be due to the size limit of Smart Cards (around 25 bytes) and so malicious cards can't be spread around.
So, to recap:
Card Generation: 2 Card Type: G Card Title: Sony Value Card ID: 999999