ASCII and Base 10 to Base 2 Conversion

Given data

• Number to convert: $0.2345$ (Base 10)
• Target base: Base 2
• Concept asked: ASCII

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Part 1: What is ASCII? (2 marks)

ASCII stands for American Standard Code for Information Interchange.

• It is a character encoding standard that assigns a unique numeric code to each character so that text can be represented, stored, and processed in computers.
• Standard ASCII uses 7 bits, giving $2^7 = 128$ possible codes (0 to 127).
• It encodes:
  • Uppercase letters A-Z (65-90)
  • Lowercase letters a-z (97-122)
  • Digits 0-9 (48-57)
  • Special/punctuation characters
  • Control characters (e.g., newline, tab, carriage return)
• Example: 'A' = 65, 'a' = 97, '0' = 48.
• Extended ASCII uses 8 bits to represent 256 characters.

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Part 2: Convert 0.2345 to Base 2 (3 marks)

Method: Repeatedly multiply the fractional part by 2; the integer part of each product gives the next binary bit (read top to bottom).

Reading the integer bits from top to bottom:

$$(0.2345)_{10} \approx (0.00111100)_2$$

Verification: $$0\cdot2^{-1}+0\cdot2^{-2}+1\cdot2^{-3}+1\cdot2^{-4}+1\cdot2^{-5}+1\cdot2^{-6}$$ $$= 0.125 + 0.0625 + 0.03125 + 0.015625 = 0.234375 \approx 0.2345 \checkmark$$

Note: This is a non-terminating binary fraction, so the answer is an approximation to 8 binary places.

$$\boxed{(0.2345)_{10} \approx (0.00111100)_2}$$

Cryptography and Firewall

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1. Cryptography (Definition)

Cryptography is the art of protecting information by transforming it (encrypting it) into an unreadable format called cipher text.

• Only those who possess a secret key can decrypt the message back into readable plain text.
• It is used as a core security mechanism -- a technical tool and technique used to implement security services.

Key Concepts in Cryptography:

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2. Why Do We Use a Firewall?

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

We use a firewall because:

• It establishes a barrier between a trusted internal network and an untrusted external network (such as the Internet), preventing unauthorized access.
• It protects systems from malicious attacks, hackers, and unauthorized intrusions.
• It filters network traffic based on defined security rules, allowing only legitimate communication.

Types of Firewalls:

1. Hardware Firewall:

• A physical device installed between the modem and the computer.
• Protects an entire network.
• Usually more expensive and harder to configure.
• Examples: Cisco PIX, Watchguard, Netscreen

2. Software Firewall:

• A software application installed on the computer system to be protected.
• Protects a single computer.
• Usually less expensive and easier to configure.
• Examples: Norton Internet Security, McAfee Security

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In summary: Cryptography secures data by making it unreadable to unauthorized users, while a firewall secures a network by controlling what traffic is allowed in or out -- both are essential components of information security.