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Why is OpenSSL able to use a key file my user shouldn't have access to? (lemmy.ca)

submitted 3 months ago by [email protected] to c/[email protected]

6 comments fedilink hide all child comments

The following command works even though I really don't think I should have permission to the key file:
$ openssl aes-256-cbc -d -pbkdf2 -in etc_backup.tar.xz.enc -out etc_backup.tar.xz -k /etc/ssl/private/etcBackup.key

I'm unable to even ascertain the existence of the key file under my normal user. I'm a member of only two groups, my own group and vboxusers.

The permissions leading up to that file:

drwxr-xr-x   1 root root 4010 Jul 31 08:01 etc
...
drwxr-xr-x 1 root root      206 Jul 14 23:52 ssl
...
drwx------ 1 root root    26 Jul 31 14:07 private
...
-rw------- 1 root root 256 Jul 31 14:07 etcBackup.key

OpenSSL isn't setuid:

> ls -la $(which openssl)
-rwxr-xr-x 1 root root 1004768 Jul 14 23:52 /usr/bin/openssl

There don't appear to be any ACLs related to that key file:

> sudo getfacl /etc/ssl/private/etcBackup.key
[sudo] password for root: 
getfacl: Removing leading '/' from absolute path names
# file: etc/ssl/private/etcBackup.key
# owner: root
# group: root
user::rw-
group::---
other::---

> sudo lsattr  /etc/ssl/private/etcBackup.key
---------------------- /etc/ssl/private/etcBackup.key

Finally, it's not just the case that the original file was encrypted with an empty file:

> openssl aes-256-cbc -d -pbkdf2 -in etc_backup.tar.xz.enc -out etc_backup.tar.xz -k /etc/ssl/private/abc.key
bad decrypt
4047F634B67F0000:error:1C800064:Provider routines:ossl_cipher_unpadblock:bad decrypt:providers/implementations/ciphers/ciphercommon_block.c:124

Does anyone know what I've missed here?

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[–] [email protected] 48 points 3 months ago (1 children)

The -k argument on my openssl accepts a passphrase, not a file. You likely encrypted with the filename as the secret, not it's contents. Perhaps you should use -kfile instead.

$ openssl aes-256-cbc -help
Usage: aes-256-cbc [options]

General options:
 -help               Display this summary
 -list               List ciphers
 -ciphers            Alias for -list
 -e                  Encrypt
 -d                  Decrypt
 -p                  Print the iv/key
 -P                  Print the iv/key and exit
 -engine val         Use engine, possibly a hardware device

Input options:
 -in infile          Input file
** -k val              Passphrase**
 -kfile infile       Read passphrase from file

[–] [email protected] 13 points 3 months ago

Wow, thanks for this. Those are two very similar flags and I missed this entirely.

Everyone - Now that you know my passphrase, be sure to keep it a secret!