Page 233 - DCAP403_Operating System

Operating System

Notes Introduction

Encryption is essentially the process of encoding – or hiding – the information you send across
the internet in a way that it can only be read by the person or website it is meant for. There are
various ways this is handled on the net.

Encryption uses a “key” - a certain sequence of numbers that is unique and only “known” by
your computer and the one you’re sending information to.
When your computer sends the information out, it scrambles it by using this key as a basis.
This scrambled information would be gibberish to anyone who didn’t have the correct key to
unscramble it at the other end.
When the information reaches its destination, it gets unscrambled by using the key. This lets the
person or website read the information correctly at the other end.
Websites that use an encrypted connection use something called SSL (Secure Sockets Layer) to
secure the information going back and forth. This is how websites like Amazon or your bank can
ensure your private information like passwords and credit card numbers are safe from prying
eyes.

There are different strengths of encryption codes. 40 bit encryption is the simplest, but it is
relatively easy to crack. Most secure websites use 128 bit encryption, which is practically
impossible to decode. You might even see 256 bit encryption is some very high-security cases.

12.1 Encryption

Encryption is a process of coding information which could either be a file or mail message in

into cipher text a form unreadable without a decoding key in order to prevent anyone except
the intended recipient from reading that data. Decryption is the reverse process of converting
encoded data to its original un-encoded form, plaintext.
A key in cryptography is a long sequence of bits used by encryption/decryption algorithms. For
example, the following represents a hypothetical 40-bit key:
00001010 01101001 10011110 00011100 01010101
A given encryption algorithm takes the original message, and a key, and alters the original
message mathematically based on the key’s bits to create a new encrypted message. Likewise, a
decryption algorithm takes an encrypted message and restores it to its original form using one
or more keys.

When a user encodes a file, another user cannot decode and read the file without the decryption
key. Adding a digital signature, a form of personal authentication, ensures the integrity of the
original message.
To encode plaintext, an encryption key is used to impose an encryption algorithm onto the data.
To decode cipher, a user must possess the appropriate decryption key. A decryption key consists
of a random string of numbers, from 40 through 2,000 bits in length. The key imposes a decryption
algorithm onto the data. This decryption algorithm reverses the encryption algorithm, returning

the data to plaintext. The longer the encryption key is, the more difficult it is to decode. For a 40-
bit encryption key, over one trillion possible decryption keys exist.
There are two primary approaches to encryption: symmetric and public-key. Symmetric
encryption is the most common type of encryption and uses the same key for encoding and
decoding data. This key is known as a session key. Public-key encryption uses two different keys,
a public key and a private key. One key encodes the message and the other decodes it. The public
key is widely distributed while the private key is secret.

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