Caesar Cipher

Try this out Caesar cipher

echo ‘Ml Trpu Svgr: uggc://xrearypensg.jbeqcerff.pbz’ | tr ‘1?a-z%#’ ‘ .n-za-m:@’

When you copy and paste in shell, the single quotes might change to dot (.) and the output might be misleeding. So, make sure you correct those single quotes.

The result of the above cypher would be as follows:

My Tech Site: https://kernelcraft.wordpress.com

Advertisements

GPG (GNU Privacy Guard) & PGP (Pretty Good Privacy)

Whenever you are downloading any software, you should look if authors/signer’s key and pgp key is available so you can import the pgp key using gpg tool and then verify if that software is signed by the author.

I have downloaded postfix softare from http://mirror.postfix.jp/postfix-release/index.html

[root@centos downloads]# ll
total 3752
-rw-r–r–. 1 root root 3827595 Jun 22 16:27 postfix-2.10.1.tar.gz (Software)
-rw-r–r–. 1 root root 280 Jun 22 16:28 postfix-2.10.1.tar.gz.sig (Sign)
-rw-r–r–. 1 root root 6390 Feb 28 2005 wietse.pgp (pgp)

You have to import the GPG key using the following command:

[root@centos downloads]# gpg –import wietse.pgp
gpg: key C12BCD99: public key “Wietse Venema ” imported
gpg: key D5327CB9: public key “wietse venema ” imported
gpg: Total number processed: 2
gpg: imported: 2 (RSA: 2)
gpg: no ultimately trusted keys found

You can now check for the imported keys as follows:

[root@centos downloads]# gpg –list-keys
/root/.gnupg/pubring.gpg
————————
pub 2048R/C12BCD99 2005-02-28
uid Wietse Venema

pub 1022R/D5327CB9 1992-09-25
uid wietse venema
uid wietse venema

Now, we are verifying the signature against the software as follows:

[root@centos downloads]# gpg –verify postfix-2.10.1.tar.gz.sig postfix-2.10.1.tar.gz
gpg: Signature made Sun 23 Jun 2013 05:28:00 AM IST using RSA key ID C12BCD99
gpg: Good signature from “Wietse Venema “
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: FF 96 4A 8C 96 88 7C 6E A4 EF AD BF 48 34 E1 BB

In the above output, we are just checking if author has signed the software and that’s confirmed by the line marked in bold (gpg: Good signature from “Wietse Venema “).

Now, you can go ahead and install/configure the software.

Linux Shell

Issue the following command to know what shell you are using by default:

[soj@centos ~]$ echo $SHELL
/bin/bash

You can check the list of installed shell on your system with the following command:

[soj@centos ~]$ chsh –list
/bin/sh
/bin/bash
/sbin/nologin
/bin/tcsh
/bin/csh

You can get the same output if you `cat /etc/shells`

You can change your default shell by issuing the following command:

Make sure you are NOT changing root user shell. That might create problems.

[soj@centos ~]$ chsh -s /bin/sh
Changing shell for soj.
Password:
Shell changed.

Before checking your default shell again, logout and login back:

sh-4.1$ echo $SHELL
/bin/sh