Download and run Tinyumbrella:
1) Make sure you Iphone is detected.
2) check "Advanced Options."
3) In new window, under "Device / Version," select whatever firmware you wish to try to save.
4) Click on "Save my SHSH." Pray Cydia has them. If you don't get an error, the SHSH hash has was saved onto your computer and Cydia.
5) Repeat to save other firmware hashes.
6) Now, click on "Display SHSHs." It should listed all hashes you have saved on your computer.