Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Securely remove files or directories in Linux
Answer:
Normally you would remove a file by using the rm command, but what if you want to make sure the file is removed securely which prevent other people from recovering it?
Use srm, e.g.
# srm confidential.txt
How to check if a RSA key file is valid
Answer:
If you have a RSA key file "test.pem" and want to know if it is a valid RSA key, you can perform a quick check
# openssl rsa -in test.pem -check
unable to load Private Key
21315:error:0906D064:PEM routines:PEM_read_bio:bad base64 decode:/SourceCache/OpenSSL098/OpenSSL098-44/src/crypto/pem/pem_lib.c:763:If it is valid, you will find
# openssl rsa -in test.pem -check
RSA key okPerform AES256 encryption on a string using command
Answer:
To encrypt a string using AES256, you can use the openssl tool.
# echo -n 'apple' | openssl enc -aes256 -k password -nosalt -iv 0 -a -p
key=1F3870BE274F6C49B3E31A0C6728957F0628DEF3179C824405825F85F5527096
iv =00000000000000000000000000000000
PMcE/8RE+RLRlQWT5tlLWA==
Check for the number of connection from a particular IP address
Answer:
You can check the total number of connections from a particular IP address:
# netstat -ntu | awk '{print $5}'| cut -d: -f1 | sort | uniq -c | sort -nr | more
It will give something like:
25 192.168.1.2
13 192.168.1.3
..
Simple file encryption with OpenSSL
Answer:
You have a single file (input.txt), and you want to encrypt it with a password, it is easy with OpenSSL.
# openssl aes-128-cbc -salt -in input.txt-out input.aes
Enter the password twice.
When you want to decrypt it, use the command.
# openssl aes-128-cbc -d -salt -in input.aes -out output.txt
