Can't read file multikeydecrypt with share key

[NickWinston123]

Steps to reproduce

1. Enable encryption
2. Upload and download files from a certain user

Expected behaviour

File should be downloaded and not result in multikeydecrypt error.

Actual behaviour

For some shared files, when trying to download a file from a certain user I get this error:
Can't read file multikeydecrypt with share key failed:error:0906D06C:PEM routines:PEM_read_bio:no start line
(EXAMPLE: https://www.bestgeardabest.tk/storage/index.php/s/Bpe8nmfrb6rdR5d/download)

Server configuration

Operating system:
Ubuntu 18.04.1 LTS

Web server:
Apache/2.4.29 (Ubuntu)

Database:
mysql Ver 15.1 Distrib 10.1.34-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

PHP version:
PHP 7.2.14-1+ubuntu18.04.1+deb.sury.org+1 (cli) (built: Jan 13 2019 10:05:45) ( NTS )

Nextcloud version: (see Nextcloud admin page)
Nextcloud 15.0.2

Updated from an older Nextcloud/ownCloud or fresh install:
Updated from version 14, but the problem occurred first on version 14. ( I thought updating would fix something)

Where did you install Nextcloud from:
From an archive from nextcloud.com

Signing status:

Signing status

No errors have been found

List of activated apps:

App list

Enabled:
  - accessibility: 1.1.0
  - activity: 2.8.2
  - cloud_federation_api: 0.1.0
  - comments: 1.5.0
  - dav: 1.8.1
  - encryption: 2.3.0
  - federatedfilesharing: 1.5.0
  - federation: 1.5.0
  - files: 1.10.0
  - files_pdfviewer: 1.4.0
  - files_sharing: 1.7.0
  - files_texteditor: 2.7.0
  - files_trashbin: 1.5.0
  - files_versions: 1.8.0
  - files_videoplayer: 1.4.0
  - firstrunwizard: 2.4.0
  - gallery: 18.2.0
  - logreader: 2.0.0
  - lookup_server_connector: 1.3.0
  - nextcloud_announcements: 1.4.0
  - notifications: 2.3.0
  - oauth2: 1.3.0
  - password_policy: 1.5.0
  - provisioning_api: 1.5.0
  - serverinfo: 1.5.0
  - sharebymail: 1.5.0
  - support: 1.0.0
  - survey_client: 1.3.0
  - systemtags: 1.5.0
  - theming: 1.6.0
  - twofactor_backupcodes: 1.4.1
  - updatenotification: 1.5.0
  - workflowengine: 1.5.0
  - end_to_end_encryption: 1.1.0
Disabled:
  - admin_audit
  - files_external
  - user_ldap

Nextcloud configuration:

Config report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "10.0.0.237",
            "98.192.18.224",
            "bestgeardabest.tk",
            "www.bestgeardabest.tk"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "15.0.2.0",
        "overwrite.cli.url": "http:\/\/10.0.0.237\/storage",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "appstore.experimental.enabled": true,
        "updater.secret": "***REMOVED SENSITIVE VALUE***",
        "maintenance": false,
        "theme": "",
        "loglevel": 2
    }
}

Are you using external storage, if yes which one: /dev/sdb mounted to /home/nextcloud

Are you using encryption: yes

Are you using an external user-backend, if yes which one: no

Operating system:

Logs

Web server error log

Web server error log

[Sat Feb 02 06:25:01.915479 2019] [mpm_prefork:notice] [pid 1790] AH00163: Apache/2.4.29 (Ubuntu) OpenSSL/1.1.0g configured -- resuming normal operations
[Sat Feb 02 06:25:01.915502 2019] [core:notice] [pid 1790] AH00094: Command line: '/usr/sbin/apache2'

Nextcloud log (data/nextcloud.log)

Nextcloud log

(was empty)

[georgehrke]

Server side encryption, not e2e, moving back to server repo.

[szaimen]

Duplicate of #8349