To quote: Sony, being as sneaky as they are decided to do a rather interesting move. As researched by Coyotebean, Sony started enforcing using a public key method of verifying KIRK data and removing the ability to load the old types of data.
As they did this, firmware 6.30+ cannot decrypt the updater and the PRX inside and therefore cannot use the index.dat spoofing to downgrade.
This application does the simple job of rebooting into the updater with a PRX that allows the updater to decrypt. A PRX that uses the pspdecrypt source and index.dat spoofing, nothing fancy.
So, I’ll stop blabering, here is the Readme: 6.35/6.31 -> 6.20 Downgrader By Davee
What does it do?
Allows users who are incontent with their firmware to downgrade to 6.20 using the Sony Updater.
How do I use it?
Copy the "PSP" folder to your PSP. The downgrader is "signed" and can be launched from OFW XMB. You need to copy the 6.20 update to PSP/GAME/UPDATE/EBOOT.PBP and for PSPgo it must be the eflash it is placed on. After setup run the downgrader and follow the onscreen instructions.
What does it technically do?
It uses the utility/power exploit to gain kernel access and reboots into the updater with a special PRX running. This PRX uses the pspdecrypt functionality to decrypt the updater PRX when needed. This allows the updater to boot in the newer firmwares.
I'm a dev, sup?
The source is in the SRC folder... if you even read this. Use the source for referencing, updating, snipping etc, remember where you got it from. Also, there is a HBL Sukkiri version, see the "Makefile" for info on the various modes, etc
bbtgp - legend. Continued updates to psardumper (pspdecrypt) and the signing application "prxEncrypter".
coyotebean - legend. Coninuted updates to psardumper (pspdecrypt) and large influence and research regarding cryptographics.
kgsws - legend. First application signed and method released.
Silverspring - legend. Lots and lots of info on KIRK where we'd still be in the dark without.
Bubbletune - BTCNF injection code and bits and bobs here ;D
You run the application at your OWN risk. I am not help accountable if you PSP messes up.
If you’re too lazy to read it then basically, you copy over the PSP folder to your PSP and put the 6.20 update to “PSP/GAME/UPDATE/EBOOT.PBP”.
THX for the +Rep. Davee said via Twitter it'll work for all PSPs at 6.31/6.35
If you want to go further than 6.20 and your PSP can handle it then when you get to 6.20 spoof it with the TN HEN to a firmware lower than the one you want to downgrade to then install the OFW for that firmware.
Downgrade 6.31 -> 6.20
run TN HEN
Install 5.00 -> 5.00M33 CFW