What are SHSH files and how does one back them up

[kevins007]

I have decided that once the jailbreak comes out for the iPhone 4 to jailbreak the thing. Now can someone please tell me what SHSH files and how to back them up?

Thank You

 

[rdiddy_25]

They let u downgrade ur firmware, i.e. downgrading from 4.0 to 3.1.3.
Caching Apple's Signature Server - Jay Freeman (saurik)