[Bug]: Multikey Encryption Breaks When Upgrading from NC26 to NC27

### ⚠️ This issue respects the following points: ⚠️

- [X] This is a **bug**, not a question or a configuration/webserver/proxy issue.
- [X] This issue is **not** already reported on [Github](https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3Abug) OR [Nextcloud Community Forum](https://help.nextcloud.com/) _(I've searched it)_.
- [X] Nextcloud Server **is** up to date. See [Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) for supported versions.
- [X] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Bug description

Hi there

We are running a multikey encrypted NC instance with some hundreds of users. Recently we upgraded from NC26 to NC27. From then on multiple users reported, that they coud not open files anymore (console logging "Cannot decrypt this file, probably this is a shared file"). After doing quiet some research, we were able to track down the problem to this cause:

In the following issue openssl_seal and rc4 were removed (https://github.com/nextcloud/server/pull/37243/files). In this PR the so called `fileKey` used for RC4 was removed after re-encrypting a file (https://github.com/nextcloud/server/blob/461f6d47e4f26f742cec2915e5aa92a2c81f605d/apps/encryption/lib/Crypto/Encryption.php#L395). Additionally a legacy format was introduced to still beeing able to open old files. However we found out that under certain contidions (resharing or move operations), the `fileKey` gets deleted _without_ re-encrypting the data, which leads to data loss. 

In particular, we could observe that the `files_encryption/key/files/[PATH]/OC_DEFAULT_MODULE` directory of affected files did contain new `[USERNAME].shareKey` files and no`fileKey` anymore. We were then able to replace the content of this directory with the old share keys and the `fileKey` (that we restored from a backup). By doing this, we could open the file again (in the webbrowser), which leads to the conclusion that the file must have lost its keys without beeing reencrypted.

We were though not able to precisely find the precise code that causes the missing reencryption. We believe that the `end` or `update` method in `apps/encryption/lib/Crypto/Encryption.php` get called without re-encrypting the file. 

Help is very much appreciated, as this currently _breaks_ all of our users data and we can't do something against that problem besides informing our customers. Thanks you very much for your support!

### Steps to reproduce
#### Install NC26 with User Key Encryption
1. Install NC 26
2. Enable the default encryption module
3. `occ encryption:list-modules` to check that the app is enabled
4. `occ encryption:disable-master-key` and accept the warning
5. `occ encryption:enable`
6. `occ encryption:encrypt-all`
7. Log out and log in again.
8. Go to personal settings -> security -> update password in security tab with the password from the CLI.

#### Create a Folder and Share
1. Create a second user
2. Create a directory, share the directory.
3. Put some files into the directory (not .md - preferrably .jpg, .pdf or .zip). Now in the `files_encryption` directory are two `[USERNAME].shareKey` and a `fileKey`.

#### Update
1. Update to NC27 
2. Create a new directory (for example `foo`).
3. Move the directory into another directory (click on the three dots -> move or copy -> move to `foo`).
4. Open the file. It will fail with a warning in the console ("Cannot decrypt...").

### Expected behavior

The files should be re-encrypted before removing the fileKeys.

### Installation method

None

### Nextcloud Server version

27

### Operating system

Debian/Ubuntu

### PHP engine version

None

### Web server

Nginx

### Database engine version

PostgreSQL

### Is this bug present after an update or on a fresh install?

Upgraded to a MAJOR version (26 to 27)

### Are you using the Nextcloud Server Encryption module?

Encryption is Enabled

### What user-backends are you using?

- [X] Default user-backend _(database)_
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Configuration report

```shell
{
    "system": {
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        },
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "cloud.wolke7.wtf"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "pgsql",
        "version": "27.1.9.1",
        "overwrite.cli.url": "https:\/\/cloud.wolke7.wtf",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "enabledPreviewProviders": [
            "OC\\Preview\\PNG",
            "OC\\Preview\\JPEG",
            "OC\\Preview\\GIF",
            "OC\\Preview\\HEIC",
            "OC\\Preview\\BMP",
            "OC\\Preview\\XBitmap",
            "OC\\Preview\\MP3"
        ],
        "preview_max_scale_factor": 2,
        "preview_max_x": 128,
        "preview_max_y": 128,
        "lost_password_link": "disabled",
        "allow_user_to_change_display_name": false,
        "skeletondirectory": "\/srv\/nextcloud-assets\/skeleton",
        "mail_smtpmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "465",
        "mail_smtpsecure": "ssl",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauth": 1,
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "activity_expire_days": 60,
        "log_type": "file",
        "loglevel": 3,
        "logfile": "\/dev\/stdout",
        "maintenance": false,
        "theme": "",
        "app_install_overwrite": [
            "end_to_end_encryption"
        ],
        "simpleSignUpLink.shown": false,
        "mail_sendmailmode": "smtp",
        "encryption.legacy_format_support": true,
        "encryption.key_storage_migrated": false,
        "default_locale": "de_CH",
        "default_phone_region": "CH",
        "updater.server.url": "https:\/\/updates.nextcloud.com\/customers\/[KEY]",
        "auth.webauthn.enabled": false
    }
}
```


### List of activated Apps

```shell
Enabled:
  - activity: 2.19.0
  - bruteforcesettings: 2.7.0
  - calendar: 4.7.1
  - cloud_federation_api: 1.10.0
  - contacts: 5.5.3
  - dav: 1.27.0
  - encryption: 2.15.0
  - external: 5.2.1
  - federatedfilesharing: 1.17.0
  - federation: 1.17.0
  - files: 1.22.0
  - files_pdfviewer: 2.8.0
  - files_reminders: 1.0.0
  - files_rightclick: 1.6.0
  - files_sharing: 1.19.0
  - files_trashbin: 1.17.0
  - files_versions: 1.20.0
  - firstrunwizard: 2.16.0
  - logreader: 2.12.0
  - lookup_server_connector: 1.15.0
  - nextcloud_announcements: 1.16.0
  - notes: 4.10.0
  - notifications: 2.15.0
  - oauth2: 1.15.2
  - password_policy: 1.17.0
  - photos: 2.3.0
  - privacy: 1.11.0
  - provisioning_api: 1.17.0
  - recommendations: 1.6.0
  - related_resources: 1.2.0
  - serverinfo: 1.17.0
  - settings: 1.9.0
  - sharebymail: 1.17.0
  - support: 1.10.1
  - text: 3.8.0
  - theming: 2.2.0
  - twofactor_backupcodes: 1.16.0
  - twofactor_totp: 9.0.0
  - twofactor_webauthn: 1.4.0
  - updatenotification: 1.17.0
  - viewer: 2.1.0
  - workflowengine: 2.9.0
Disabled:
  - admin_audit: 1.17.0
  - circles: 27.0.1 (installed 22.1.1)
  - comments: 1.17.0 (installed 1.10.0)
  - contactsinteraction: 1.8.0 (installed 1.3.0)
  - dashboard: 7.7.0 (installed 7.0.0)
  - end_to_end_encryption: 1.13.1 (installed 1.13.1)
  - files_external: 1.19.0
  - survey_client: 1.15.0 (installed 1.4.0)
  - suspicious_login: 5.0.0
  - systemtags: 1.17.0 (installed 1.10.0)
  - user_ldap: 1.17.0
  - user_status: 1.7.0 (installed 1.0.1)
  - weather_status: 1.7.0 (installed 1.0.0)
```


### Nextcloud Signing status

```shell
No errors have been found.
```


### Nextcloud Logs

_No response_

### Additional info

_No response_

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[Bug]: Multikey Encryption Breaks When Upgrading from NC26 to NC27 #45182

derschiw
openedon May 4, 2024

⚠️ This issue respects the following points: ⚠️

Bug description

Steps to reproduce

Install NC26 with User Key Encryption

Create a Folder and Share

Update

Expected behavior

Installation method

Nextcloud Server version

Operating system

PHP engine version

Web server

Database engine version

Is this bug present after an update or on a fresh install?

Are you using the Nextcloud Server Encryption module?

What user-backends are you using?

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

Assignees

Labels

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Projects

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