[Huawei P9 Guides, News, & Discussion] boxcat:
How I unbricked "Decryption unsuccessful" The password is correct but... (Apps2SD)

Hello, I don't usually post in tech forums, I usually the guy that only reads,

but this is the time when i could not find the straight answer to my problem and had to google the solution out of similar posts, so I decided to glue everything together and write my solution to this particular situation,

so I might save a lot of time to someone who got in exact or similar situation.

Sorry for my crappy English, but here we go.

What this post trying to solve:

You stuck at boot loop: "Decryption unsuccessful" The password that you entered is correct but unfortunately your data is corrupt.

and how to make it work Apps2SD with Huawei P9 SD card with enabled password protection.

Basically my Huawei P9 (EVA L-19) with Android 7.0 Nougat got running out of internal space, and i am really a heavy user on apps. Kirin 955 handles just fine as long as it has at least 10Gb of internal free space.

I have SD card 64Gb, but huawei stopped support, native move apps to SD, long time ago. My device is rooted, so I was searching for a solution. There is few apps that can transfer your internal memory apps to SD by using root, but the one that actually worked for me is Apps2SD. The thing is, my SD card is password protected (Huawei native function) I want to keep this function in case of device getting stolen.

Problem is, many third party apps that move your apps to SD, does not know anything about Huaweis SD card password feature. In fact (as far as i tested) only Huawei phone allows you to enter password and show contents of SD card, no PC, or for example Samsung phone will recognize this SD card.

So i was messing with Apps2SD, partitioned my SD card in to 2 primary partitions, 1- exfat, 2- Ext3. It works kinda fine, but after reboot, there is delay, Huawei unlocks SD card after main boot part, and Apps2SD does not understand this and show that it failed to mount second partition.

In this case, Apps2SD starts giving you solutions, one of them is this ADVANCED mounting option. It does not tells u about any dangers, nothing really.

I chose that option to see if it will be able to see second partition contents faster, rebooted - boom bricked.

You see the message: "Decryption unsuccessful" and asks you for decryption password. It might be SD card password, not sure, it does not matter, because you can type ANYTHING and it always say:

"The password that you entered is correct but unfortunately your data is corrupt". And gives you only option: fully data factory reset. Now hold your horses, dont press that. I just knew that this is bull**** and no way

my personal data is corrupted, its just some hadshake issue. (I was right i fully recovered everything up n running)

Assuming you got in this mess, your device must be rooted and you probably have TWRP recovery, cause Apps2SD work only with rooted devices.

To recover from "Decryption unsuccessful" boot message and restore all data and settings:

Got to TWRP recovery by holding power button and volume UP (after phone vibrates, hold both buttons 2sec more and then release power button, and then after 2sec more release volume up, cause if

you do this too fast, u will end up in wifi recovery by Huawei, and it wont work anyway cause your device rooted).

Then go to advanced and file manager, locate sdcard folder (this will be internal memory, not external), you should be able to see all of your personal files! Copy them to flash drive by connecting with OTG.

What we gonna do now is: do a full nandroid backup: TWRP, backup, check: BOOT, SYSTEM, DATA. and do a backup to flash drive connected with OTG or hard drive if it works for u.

After backup is done, go to WIPE, select format data, select DATA partition and see what original file system it uses. Now format in any other system, then reformat again to your original file system.

DATA partition somehow lost its encryption handshake key and this caused the problem, reformatting fixes it.

Now do a full wipe as if you would install new rom, wipe: system, data, storage, cache, dalvic cache.

Restore your previous nandroid backup, reboot to system,now your phone should boot with all the apps and settings just as you left.

You might be missing some pictures and other media in main storage, just connect your P9 with usb cable to pc, and restore previously backed up media from flash drive manually in pc interface (copy paste, replace all),

some small minority files might wont copy, don't worry about it, Im not sure but they are mostly indexing files, all ur media will be back in place.

Now, how to make Apps2SD work with this configuration?

Don't use that advanced method to find SD cards second partition, use any of first 3, the 3rd one worked for me just fine, cause its SU library based one.

Don't move your apps fully to SD, or they will "disappear", move everything except APK, ODEX, DEX (Lib is optional, you usually can move this one just fine). SO basically app core will stay in main storage but cache and app data will be on second SD card. This way, after you reboot your phone, you will have to wait like 3mins and App2SD will link your files to apps itself just fine. It might will show some errors right after reboot, but after Huawei unlocks its card, files will be linked, and apps wont be "gone" cause app core still stays in main storage.

This way i managed to save a lot of space and move most of app storage to SD card, P9 became very responsive, even in 2018 this is a really fast smartphone.

Sorry for a messy post, I'm not a writer, but I hope this helps to someone!