QUOTE(cheezels21 @ Apr 21 2011, 11:26 AM)
firstly, thanks for all the helpful response.
Yes, I've JB my 3gs and I've cydia...that was why I was also asking abt how to backup cydia apps.
Why I asked abt SHSH blob was that some JB tutorials didn't mention abt needing a valid blob and having to using TinyUmbrella as the server during the firmware update. What confuses me is that in one of the JB steps via Redsnow we need to select the 4.2.1 IPSW and it has option to install cydia. I was under the impression we can actually do the firmware upgrade through Redsnow and JB at the same time. Is this right? Or the jailbreaking and firmware upgrade is done separately?
I was re-reading your post and I thought I'd write a reply that can clear some of the confusions.
1, Most of the tutorials (iClarified.com or redmondpie) will guide you on how to jailbreak on the latest firmware version at the time. So right, now ... the latest firmware version that can be jailbroken is 4.3.2 (current with what Apple has just released).
2. Once Apple has released the latest firmware, the old jailbreak guides (4.3.1/4.2.1/4.0 etc etc) will be outdated and must be used cautiously. This is because, everytime you jailbreak, Apple will verify the firmware you just installed on the iPhone and if it's not the latest version, they will not allow you to proceed and your jailbreak will fail.
This is why, if you are trying to "update" to 4.2.1 (from 3.1.2), you will need to have the 4.2.1 SHSH blobs saved and TU running the TSS Server as the TSS Server will disguise itself as the Apple Signing Server and allow you to "update" to 4.2.1
I hope this will help some who are trying to "update" to a lower firmware than what is currently released by Apple.
Same thing with downgrade ... you need to have the TSS server running (and SHSH saved of course)