Now V2.17 3uTools supports downgrading iPhone 4s and iPad 2 to iOS 6.1.3 after jailbreak without SHSH. After you downgrade to iOS 6.1.3, you can check iOS software update on your iDevice to upgrade to iOS 8.4.1.
Requirements
1. Download and install the latest version of 3uTools.
2. Download the corresponding custom firmware for your iDevice;
iPhone4s：ota_iPhone4,1.ipsw
iPad 2：ota_iPad2,1.ipsw ota_iPad2,2.ipsw ota_iPad2,3.ipsw
3. Jailbreak your iDevice: Please update your iDevice to iOS 9.3.5 to jailbreak.
4. This downloading tutorial only applies to iPhone 4s and iPad 2 (Product type: iPad2.1, iPad 2.2 and iPad 2.3).
Operations Step 1 Launch Cydia and add source: repo.hackyouriphone.org to enter KDFU mode (Check the detailed tutorial)
Step 2 Launch 3uTools and go to “Flash & JB” -> “Pro Flash”, click “Import Firmware” and select the firmware you have already downgraded.
Step 3 After you import the firmware, click “Flash” on the right bar.
View the complete tutorial here: Downgrade iPhone 4s / iPad 2 to iOS 6.1.3 Using 3uTools