In this part of my iOS downgrade tutorial, I'll explain you how to downgrade an iPhone 4 to any firmware (beta included) without shsh.

Kind of downgrade: TETHERED. You must boot your device with a computer.

• A windows computer/vm
• The ipsw file of the version you want to go to. You can download firmware files from ipsw.me
• The ipsw file of the latest version for your device that apple is signing. You can download firmware files from ipsw.me
• iTunes 11.0.5
• Suns9: a tool to create the custom ipsw. Download here
• iReb: a tool to get into pwned dfu mode. Download here

Procedure

• Extract Suns9 from the zip file and put the folder on your desktop.
• Extract "Suns9_GUI-v1.0.8.zip" and put the folder on your desktop.
• Put both the latest ipsw and the old ipsw in the same folder of Suns9
• Run "Suns9_GUI.exe" as administrator
• Set the original iOS 7.1.2 ipsw first
• and then select the target ipsw.
• Now go here and copy the root filesystem key for your firmware/device combo.
• Paste the key in Suns9
• Press on build downgrade ipsw
• Wait while it does all the stuff
• When it's done, put your iPhone in DFU mode
• Now open iReb as administrator and choose iPhone 4
• When iReb is done, open iTunes and press shift+restore
• Choose the custom ipsw Suns9 created
• Restore.

Booting

• When the restore will be completed, your device will reboot and will be stuck on an apple logo. That's normal.
• Put your iPhone in dfu mode
• Now, the method to boot your device depends on what version of iOS you installed.
• If you installed iOS 6.x or lower, use redsn0w to boot it.
• If you installed iOS 7.x , use opensn0w to boot it.
• If the provided methods aren't working, you could try booting with futurerestore, as shown (soon)

Thanks to

@iSuns9 and @iLov3rain for Suns9

@iH8sn0w for iReb

iPhone dev team for redsn0w

@winocm for opensn0w

@ichitaso for opensn0w GUI

Everyone else and sorry if I forgot someone.