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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 20.0.5): 21.0.2.1
Operating system and version (eg, Ubuntu 20.04): Debian GNU/Linux 10
Apache or nginx version (eg, Apache 2.4.25): nginx/1.14.2
PHP version (eg, 7.4): PHP 7.4.21
The issue you are facing:
I’ve been seeing random file decryption issues on my Nextcloud instance (with OC_DEFAULT_MODULE enabled). For a concrete example from earlier today: after a file copy on the web interface by a user (my wife ;)), on first attempting loading the file she (the same user) got an 500 error. In the log the following is visible:
Can not decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.
Mind you, the user is the same, so resharing it does not really make sense.
Additional observations:
- What I also noticed is that while the file itself (encrypted version) was present in the folder structure, no corresponding keys were present at all in the corresponding files_encryption/keys folder
- As before (with some success), I tried an occ files:scan on the folder containing this file; it did not fix the problem but somehow 6 “ghost” files appeared! Also with no corresponding files_encryptions/keys to them, and also giving the same decryption error on open attempt.
- A Redis configuration has been active on this server
Is this the first time you’ve seen this error? (Y/N): N
Steps to replicate it:
Unfortunately I can’t see a pattern for replication; it sometimes appears on file copy, sometimes on upload.
Any help/pointer would be highly appreciated!
The output of your Nextcloud log in Admin > Logging:
{"reqId":"zLk3xkCoFD0Uo9wIfxVH","level":4,"time":"2021-07-07T18:43:21+00:00","remoteAddr":"***sensitive***","user":"***sensitive***","app":"webdav","method":"GET","url":"***filename***","message":{"Exception":"OC\\Encryption\\Exceptions\\DecryptionFailedException","Message":"Can not decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.","Code":0,"Trace":[{"file":"***sensitive***/public_html/lib/private/Files/Stream/Encryption.php","line":520,"function":"decrypt","class":"OCA\\Encryption\\Crypto\\Encryption","type":"->","args":["*** sensitive parameters replaced ***"]},{
"file":"***sensitive***/public_html/lib/private/Files/Stream/Encryption.php","line":318,"function":"
readCache","class":"OC\\Files\\Stream\\Encryption","type":"->"},{"function":"stream_read","class":"
OC\\Files\\Stream\\Encryption","type":"->"},{"file":"***sensitive***/public_html/apps/files_external
/3rdparty/icewind/streams/src/Wrapper.php","line":55,"function":"fread"},{"file":"***sensitive***/pu
blic_html/apps/files_external/3rdparty/icewind/streams/src/CallbackWrapper.php","line":96,"function
":"stream_read","class":"Icewind\\Streams\\Wrapper","type":"->"},{"function":"stream_read","class":
"Icewind\\Streams\\CallbackWrapper","type":"->"},{"file":"***sensitive***/public_html/3rdparty/sabre
/http/lib/Sapi.php","line":112,"function":"stream_copy_to_stream"},{"file":"***sensitive***/public_h
tml/3rdparty/sabre/dav/lib/DAV/Server.php","line":490,"function":"sendResponse","class":"Sabre\\HTT
P\\Sapi","type":"::"},{"file":"***sensitive***/public_html/3rdparty/sabre/dav/lib/DAV/Server.php","l
ine":253,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"***sensitive***/public_html/3rdparty/sabre/dav/lib/DAV/Server.php","line":321,"function":"start","class":"Sabre\\
DAV\\Server","type":"->"},{"file":"***sensitive***/public_html/apps/dav/appinfo/v1/webdav.php","line
":84,"function":"exec","class":"Sabre\\DAV\\Server","type":"->"},{"file":"***sensitive***/public_htm
l/remote.php","line":167,"args":["/home/cld_wkrm/public_html/apps/dav/appinfo/v1/webdav.php"],"function":"require_once"}],"File":"***sensitive***/public_html/apps/encryption/lib/Crypto/Encryption.php
","Line":373,"Hint":"Cannot decrypt this file, which is probably a shared file. Please ask the file
owner to reshare the file with you.","CustomMessage":"--"},"userAgent":"Mozilla/5.0 (X11; Ubuntu;
Linux x86_64; rv:89.0) Gecko/20100101 Firefox/89.0","version":"21.0.2.1"}
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => '***removed***',
'passwordsalt' => '***removed***',
'secret' => '***removed***',
'trusted_domains' =>
array (
***removed***
),
'datadirectory' => '***removed***',
'tempdirectory' => '***removed***',
'overwrite.cli.url' => '***removed***',
'dbtype' => 'mysql',
'version' => '21.0.2.1',
'dbname' => '***removed***',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => '***removed***',
'dbpassword' => '***removed***',
'installed' => true,
'maintenance' => false,
'mail_smtpmode' => 'smtp',
'mail_smtpauthtype' => 'LOGIN',
'mail_from_address' => 'cloud',
'mail_domain' => '***removed***',
'mail_smtphost' => 'localhost',
'mail_smtpport' => '25',
'theme' => '',
'loglevel' => 1,
'memcache.local' => '\\OC\\Memcache\\APCu',
'mysql.utf8mb4' => true,
'app_install_overwrite' =>
array (
0 => 'apporder',
),
'mail_sendmailmode' => 'smtp',
'has_rebuilt_cache' => true,
'memcache.distributed' => '\\OC\\Memcache\\Redis',
'redis' =>
array (
'host' => '127.0.0.1',
'port' => 6379,
'dbindex' => 0,
'password' => '***removed***',
'timeout' => 1.5,
),
'memcache.locking' => '\\OC\\Memcache\\Redis',
'encryption.legacy_format_support' => true,
'encryption.key_storage_migrated' => false,
'default_phone_region' => 'NL',
);
The output of your Apache/nginx/system log in /var/log/____:
***removed*** - - [07/Jul/2021:20:43:19 +0200] "POST /apps/text/session/sync HTTP/2.0" 200 246 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:89.0) Gecko/20100101 Firefox/89.0"
***removed*** - - [07/Jul/2021:20:43:21 +0200] "GET /remote.php/webdav/***filename*** HTTP/2.0" 500 14820 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:89.0) Gecko/20100101 Firefox/89.0"
***removed*** - - [07/Jul/2021:20:43:24 +0200] "POST /apps/text/session/sync HTTP/2.0" 200 246 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:89.0) Gecko/20100101 Firefox/89.0"