The Basics of Cryptography

The Basics of Cryptography
by tHe mAnIaC
dancho@mbox.digsys.bg
maniac@forbidden.net-security.org


This guide is for educational purposes only I do not take any responsibility about anything happen after reading the guide. I'm only telling you how to do this not to do it. It's your decision. If you want to put this text on your Site/FTP/Newsgroup or anything else you can do it but don't change anything without the permission of the author.

A word from the author:
I hope you like my texts and find them useful. If you have any problem or some suggestion feel free to e-mail me but please don't send mails like "I want to hack the US government please help me" or "Tell me how to bind a trojan into a .jpg"

Be sure if I can help you with something I will do it.

Table of Contents

1. What is this text about?
2. About Encryption and how it works
3. About the Cryptography and PGP
4. Ways of breaking the encryption

-- Bad pass phrases
-- Not deleted files
-- Viruses and trojans
-- Fake Version of PGP


1.What is this text about?

In this text I'll explain you everything about encryption,what is it,PGP, ways that someone can read your encrypted files etc.Every hacker or paranoid should use encryption and keep the other from reading their files.The encryption is very important thing and I'll explain you how can someone break and decrypt your files.

2.About Encryption and how it works

The Encryption is very old.Even Julius Caesar used it when he was sending messages because he didn't trust to his messengers.You see encryption is everywhere,when you watch some spy film you see there's always a computer with encrypted files or some film about hackers when the feds busted the hacker and they see all of the hacker's files are encrypted.

When you have simple .txt file that you can read this is called "plain text". But when you use encryption and encrypt the file it will become unreadable by the time you don't enter the password.This text is called cipher text. The process of converting a cipher text into plain text is called decryption.

Here's a little example:
Plain text ==>Encryption==>Ciphertext==>Descryption==>Plaintext

This example shows you the way when you encrypt and decrypt a file.

3.About the Cryptography and PGP

Cryptography is science that use the mathematics to encrypt and decrypt data.This science let you keep your files and documents safe even on insecure networks like the Internet. The cryptography can be weak and strong.The best is of course the strong one.Even when you use all the computers in the world and they're doing billion operations in second you'll just need BILLIONS of years to decrypt strong encryption.

PGP (Pretty Good Privacy) is maybe the best encryption program to encrypt your files and documents. It work in this way:

When you encrypt one file with PGP,PGP first compress the file.This saves you disk space and modem transmition.Then it creates a session key.This session key works with a very secure and fast confidential encryption algorithm to encrypt the file.Then the session key is encrypted with the recipient's public key.
PGP ask you for pass phrase not for password.This is more secure against the dictionary attacks when someone tries to use all the words in a dictionary to get your password.When you use pass phrase you can enter a whole phrase with upper and lowercase letters with numeric and punctuation characters.

4.Ways of breaking the encryption

PGP has been written for people that want their files encrypted for people that want privacy. When you send an e-mail it can be read from other people if you use PGP only the person for who is the message will be able to read it.

Now you know many things about PGP and the encryption but you may like to know can someone break it and read your private texts and files.In fact if you use all the computers in the world to decrypt a simple PGP message they'll need 12 million times the age of the universe to break it. You see this is the BEST the encryption is so strong noone can break it. The people that program it has done their work now everything depends on you.


-- Bad pass phrases --

The algorithm is unbreakable but they're other ways to decrypt the text and read it. One of the biggest mistakes when someone writes his/her pass phrase is that the pass phrase is something like : "John" "I love you" and such lame phrases.Other one are the name of some friend or something like that.This is not good because this is pass phrase not password make it longer put numbers and other characters in it.The longer your pass phrase is the harder it will be guessed but put whole sentences even one that doesn't make sense just think in this way: Someone is brute-forcing thousands of pass phrases from a dictionary therefore my pass phrase should be someone that is not there in the dictionary something very stupid like:

hEllowOrld33IjustwanTtoteLLtoev3ryon3thatI'maLamErandI'mahacKer666

This is easy to remember because it's funny and there are only a few numbers but you may not use upper and lowercase characters.I hope you know will put some very good pass phrase and be sure noone will know it.
Another mistake is that you may write the pass phase on a paper and if someone find it you'll loose it and he/she will be able to read your encrypted files.

-- Not deleted files --

Another big security problem is how most of the operating systems delete files.So when you encrypt the file you delete the plain text and of course leave the encrypted one. But the system doesn't actually delete the file.It just mark those blocks of the disk deleted and free. Someone may run a disk recovery program and still see all the files but in plaintext.Even when you're writing your text file with a word editor it can create some temporary copies of it.When you close it these files are deleted but as I told you they're still somewhere on your computer. PGP has tool called PGP Secure Wipe that complete removes all deleted files from your computer by overwriting them.In this way you'll only have the encrypted files on your computer.

-- Viruses and Trojans --

Another dangerous security problem are the viruses and the trojans.So when you infect with a trojan the attacker may run a key logger on your system.

** Note **
A key logger is a program that captures all keystrokes pressed by you then saves them on your hard drive or send them to the attacker

So after the attacker run it he/she will be able to see everything you have written on your computer and of course with your PGP pass phrase.
There are also a viruses designed to do this.Simpy record your pass phrase and send it back to the attacker.

-- Fake Version of PGP --

Another security problem is the PGP source that is available so someone can make a fake copy of it that is recording your pass phase and sending it back to the attacker.The program will look real and it will work but it may also have functions you even don't know about.
A way of defending of these security problems is to use a trojan and a virus scanner.You should also be sure your computer is clean from viruses and trojans when you install PGP and also be sure you get PGP from Network Associates Inc. not from some other pages.

So now I hope you understand that PGP can't be braked but if you use it wisely and be sure your pass phrase is good one,you're not infected with viruses or trojans and you're using the real version of PGP you'll be secure.


tHe mAnIaC is a member of Black Sun Research Facility (BSRF).
Get more BSRF tutorials at http://blacksun.box.sk.