Decrypt encrypted message with wrong password and have no error output.

ddenial · 08-06-2020, 11:10 AM

Hello All

I have some encrypted text in my shell script. I want to decrypt it on-the-fly from within shell script provided the correct password.

If the correct password is provided, then display message. But if the wrong password is given, just echo the 'Wrong password' message and exit shell script.

These are the steps I followed.

Code:

$ cat cleartext.txt 
This is a very important secret message for authorized eyes only:

   "Why Did the Chicken Cross the Road?"

Burn After Reading.

$ openssl aes-256-cbc -a -salt -pbkdf2 -in cleartext.txt -out secret.txt

$ cat secret.txt 
U2FsdGVkX18KYDskEKxri/xwUQ0m7Svp5UrlFs5wjVqrLVOwfpFIHa2cu3Sl+l6M
eQ2SdNyg2j3KzWOqMNu83cX5LS+HWvs5kPKQKL3j+qiI3ucUElVNc0JfG59y8+tn
3WMMDpb5JD+I9T5vMWz5E7OA658M0xkgMng0WYNtXBFeBOk8K1caSkFNuRHmUfef
NOGNukvVmHJ4gvdcRoQjJg==

Now I put this in my script:

Code:

$ cat showmsg.sh 
#!/bin/bash

MSG() {
cat <<EOF
U2FsdGVkX18KYDskEKxri/xwUQ0m7Svp5UrlFs5wjVqrLVOwfpFIHa2cu3Sl+l6M
eQ2SdNyg2j3KzWOqMNu83cX5LS+HWvs5kPKQKL3j+qiI3ucUElVNc0JfG59y8+tn
3WMMDpb5JD+I9T5vMWz5E7OA658M0xkgMng0WYNtXBFeBOk8K1caSkFNuRHmUfef
NOGNukvVmHJ4gvdcRoQjJg==
EOF
}

# Store decrypted tags in variable. Needs password.
VAR=$(MSG | openssl aes-256-cbc -a -d -salt -pbkdf2 2>/dev/null)

if [[ $? -eq 0 ]] ; then
        echo
        echo -e ">>> And The Message Is <<<"
        echo "${VAR}"
        echo
	echo "And do some othe stuff for later"
else
        echo "Wrong password! Exiting..."
        exit 1
fi

Now, if I give correct password 'abcd', then the message will be display properly. But if I give wrong password, say 'aaaa', I get some error message. Why?

Code:

$ ./showmsg.sh 
enter aes-256-cbc decryption password: abcd

>>> And The Message Is <<<
This is a very important secret message for authorized eyes only:

   "Why Did the Chicken Cross the Road?"

Burn After Reading.

And do some othe stuff for later

$ ./showmsg.sh 
enter aes-256-cbc decryption password: aaaa
./showmsg.sh: line 13: warning: command substitution: ignored null byte in input
Wrong password! Exiting...

What is this 'command substitution: ignored null byte in input' error? How do I solve this?

Thanks

ddenial · 08-06-2020, 02:24 PM

If I could at least disable this stupid error message with symbols all over my terminal when given with the wrong password, I can make some improvements in my script.

Code:

[neon@fed ~/Documents]$ openssl aes-256-cbc -a -d -salt -pbkdf2 -in secret.txt 2>/dev/null
enter aes-256-cbc decryption password: aaaa
-�)�3;#^;��^$ ���
,�e�U9b5_�> ��.p�O$_@��>�/���8ަ2�xؿl�ä����M��/;ȇ�6퐙d%�Pn8F����plw�&c"'ݎ�CB����}�M�p�:�[neon@fed ~/Documents]$

Can anyone throw some lights on how to disable this horrible output error from displaying when a wrong password is given? I tried all I/O redirection I can think of in my limited understanding to no avail.

Thanks.