I0n1c has posted his untether for the iOS 4.3.1 jailbreak but you’ll have to be able to crack the zip password to access it.
Some people still did not get that the untether.zip “leak” was intentional. Have fun bruteforcing a 30 character AES password.
Ehmm it is a simple ZIP file with AES encryption. winzip / 7z support that.
The untether is downloadable at http://antid0te.com/untether.zip (but only if you can crack the ZIP password)
The problem is: I forgot the password.
It is only mean if you are really so desperate that you cannot wait for the dev-team to release redsn0w with it.