Nextcloud (Owncloud) fix encryption

This small program can help to restore inaccessible files encrypted with standard encryption method.

Overview

Nextcloud's encryption requires a unique "file key", the size of the decrypted file and the version number to decrypt a file.

If you lost the file size of the decrypted file and or the version number this php script might help you.

Requirements:

• Linux or rather a UNIX-System to run it on (Windows is not supported)
• PHP... :)
• the script has to have access to the Nextcloud data directory including the
  • private key
  • share key
  • file key
• read/write access to the database of Nextcloud

There are two possible methods to that.

First method

The first is build around the function fixUnencryptedSize from the Nextcloud sourcecode. This will require the password of the user whose files you want to decrypt.

Required config values:

• data_dir
• instance_id
• instance_secret
• current_db

File to execute: main.php USER [-f "/path/to/optional/file"]

Second Method

If you have a database backup with the files in working order you can try this one.

Required config values:

• data_dir
• current_db
• backup_db

File to execute: main-w-db.php USER [-f "/path/to/optional/file"]

Get started

• clone the repo or download it as a zip
• copy config-sample.php to config.php and enter the correct data in the fields
• run the file of your selected method with parameter of the user and optimally a file option if only want to fix a single file

Examples:

• php /home/admin/nextcloud-fix-decryption/main.php frank -f "/var/www/html/nextcloud/data/frank/Pictures/2017211101-151310-0.jpg"
• php /home/admin/nextcloud-fix-decryption/main-w-db.php bela-m

I suggest to run debug (dry-run) first, then "test", check the file for success and lastly to run a full cycle.

Not implemented at the present time

• non UNIX Systems (e.g. Windows)
• recovery key support
• old file versions

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I hope this helps with your recovery. Albeit as a starting point.