Linux with Operating System Concepts

filename
where 
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is the name of your LaTeX file. Bibliography entries will appear in your doc-
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5.5 ENCRYPTION SOFTWARE
In this section, we examine some of the encryption software available in Linux concentrat-
ing on openssl and other supporting tools. Before we look at the software, let us consider 
what encryption is and why and how we can use it.
5.5.1 What Is Encryption?
Encryption is a process of taking information in the form of a string of characters (whether 
ASCII, Unicode, binary, or other) and altering it by some code. The encoded message would 
make the information hard to understand if intercepted. Encryption and decryption are 
the translation processes of taking information and placing it into a coded form and taking 
a coded message and restoring the original form, respectively.
We want to apply encryption in our telecommunication to ensure that secure informa-
tion such as passwords, credit card numbers, and even confidential text information can-
not be viewed if intercepted during communication. This is necessary because the Internet 
is not set up to broadcast information in a secure form. We might also encrypt data files on 
our computer in case a computer was to fall into others hands.
Once encrypted, the information should hopefully be in a nearly unbreakable code. For 
a person to be able to view the original information without the code, the person would 
have to try to break the code. This might require trying all possible permutations of a code. 
This attempt at breaking a code is known as a 
brute-force
approach. The number of combi-
nations that such an attack might require depends on the encryption algorithm. The best 
encryption algorithms used today could take dozens of supercomputers more than 10
18
(a 
billion billion) years to break.
*
*
As reported by 
EE Times
at http://www.eetimes.com/document.asp?doc_id 
=
1279619.

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Linux with Operating System Concepts
There are two general forms of encryption algorithms used today: 
symmetric key encryp-
tion
(also known as 
private
key encryption) and 
asymmetric key encryption
(also known 
as 
public
key encryption). The 
key
is a mathematical means of encrypting and decrypt-
ing information. The encryption algorithms used today apply a numeric key that might 
be 80, 128, or 256 bits in length. Various algorithms use different sized keys and apply 
them in different ways. Symmetric key encryption algorithms include advanced encryp-
tion standard (AES), the data encryption standard (DES, now out of date), and the triple 
data encryption algorithm (triple DEA which applies DES in three ways). Asymmetric key 
encryption algorithms include RSA (abbreviations of the three inventors, Ron Rivest, Adi 
Shamir, and Leonard Adleman), ElGamal, and the digital signature algorithm (DSA).
Figure 5.8 illustrates the use of symmetric key encryption (top half of the figure) and 
asymmetric key encryption (bottom half of the figure). In symmetric key encryption, there 
is a single key that handles both encryption and decryption. Since this key is the only pro-
tection to ensure the security of the encrypted data, it is known as a 
private
key, one that 
should be held securely so that the data cannot be examined. You might use symmetric 
key encryption to encrypt your data files on your computer or to transmit data to another 
person over the Internet who knows the key.
For E-commerce, we need a mechanism, whereby a customer can encode confidential 
data such as a credit card number and submit that information over the Internet. The 
concern here is that if we were to use symmetric key encryption, then we would be giving 
the key to the customer who could potentially then use that key to decrypt other people’s 
messages. So, a separate mechanism is needed, one where we have a public key that can 
be given to anyone and a private key. In asymmetric key encryption, the 
public
key is used 
to encrypt messages but cannot be used to decrypt messages. The private key is used to 
decrypt messages as well as generate the public key. Therefore, the organization creates a 
private key and uses it to generate a public key. The private key is kept secure and the public 
key is provided to the customers.
You have no doubt used asymmetric, or public key, encryption yourself although you 
may be unaware of any of the actual mechanisms behind it because these are taken care of 
by your web browser. You can view the public key provided to you by an organization by 
12345678901234567
Original message
Key
Key
Encrypted message
Original message
12345678901234567
#A1c8eF!7ab8zzeiZ2*Mp3
12345678901234567
Original message
Encrypted message
Public key
Private key
Original message
12345678901234567
F8&cc%75ona!rheVb
FIGURE 5.8 
Symmetric (public) key encryption (top) and asymmetric (private) key encryption 
(bottom). (Adapted from Fox, R.