- Since the release of PS3 Firmware v3.55
there is no sense in keeping the master key a secret any more - it has been released, along with unencrypted payloads, and a promise to release the source-code by PS3YES for a free PSGrade
/ PSGrade PS3 Hex Codes
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Of note, the downgrade hex will only work on PS3's with a firmware of 3.50 or below.
The same team which brought the PSN spoof for online support of jailbreaks now has also brought us a Free Downgrade HEX for the PS3! PS3YES has released un-encrypted HEX files for downloading.
They promise open-source code to be release soon, but find below pre-compiled HEX files: