iOS 5 beta has officially become the iPhone jailbreaking community’s worst nightmare. A post on the Dev-Team Blog has confirmed the latest build prevents both downgrading firmwares and untethered jailbreaks.
Without diving too deep into the technicalities, the LLB and iBoot stages of iOS 5 depend on the authenticity of APTicket. Since APTicket is uniquely generated at each restore (and boot), Apple alone holds the keys to properly sign a pre-restore APTicket. Bottom line: a firmware downgrade or untethered jailbreak with iOS 5 is near impossible.










