Why is OpenSSL able to use a key file my user shouldn't have access to?

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?

View original on lemmy.ca

Comments6

theit8514

lemmy.world

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

NotAnArdvark reply

lemmy.ca

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!

418teapot

lemmy.world

On my machine at least man openssl shows that -k is for specifying the password you want to derive the key from, so in that case I think you are literally using the string /etc/ssl/private/etcBackup.key as the password. I think the flag you want is -kfile.

You can verify this by running the command in strace and seeing that there is no openat call for the file passed to -k.

Edit: [email protected] beat me to it while I was writing out my answer :)

Maxy

lemmy.blahaj.zone

I have about 0 experience with openssl, I just looked at the man page (openssl-enc). It looks like this command doesn’t take a positional argument. I believe the etcBackup.key file isn’t being read, as that command simply doesn’t attempt to read any files without a flag like -in or -out. I could be wrong though, see previously stated inexperience.

metiulekm reply

sh.itjust.works

It seems OP wanted to pass the file name to -k, but this parameter takes the password itself and not a filename:

       -k password
           The password to derive the key from. This is for compatibility with previous versions of OpenSSL. Superseded by the -pass argument.

So, as I understand, the password would be not the first line of /etc/ssl/private/etcBackup.key, but the string /etc/ssl/private/etcBackup.key itself. It seems that -kfile /etc/ssl/private/etcBackup.key or -pass file:/etc/ssl/private/etcBackup.key is what OP wanted to use.

refalo reply

programming.dev

Oh that's nasty. I bet a quick github search would turn up some people making the same mistake.