Network and Data Security -

Network and Data Security -

Network and Data Security IGCSEICT.INFO Network and Data Security If your computer is connected to a network, other people can connect to your computer. A person who gains unauthorised access to a computer system is

often called a hacker. Physical Security The first thing to make sure of is that no unauthorised people can physically access (sit down in front of) any of the computers on your network. For example, by keeping office doors locked.

Username and Password Effective passwords must be chosen that are not easy to guess Passwords should be a random combination of lowercase letters, uppercase letters and numbers (and symbols if this is allowed) Weak passwords: password, 123456, david, 27dec1992 Strong passwords: s63gRdd1, G66ew$dQ, gdr298783X

Tips Creating A Strong Password Think of a phrase that you will never forget My favourite food is chocolate ice cream Take the first letter of each word mfficic Change some letters to similar numbers: I to 1, o to 0, s to 5, etc.

and make some letters (e.g. the first and last) uppercase Mff1c1C Securing Your Data Often we have data that is private or confidential. This data needs to be protected from being viewed by unauthorised people.

This is especially true if the data is to be sent via a public network such as The Internet. The best way to protect data is to encrypt it Data Encryption Encryption is the process of converting information into a form that is meaningless to anyone except holders of a key.

For example, if Alice wants to send important, personal messages to Bob, she must go through the following steps... Data Encryption First Alice needs to generate a secret key. The key is usually a very long, random number.

Data Encryption Alice must then give a copy of this key to Bob. She must make sure that nobody else can get to the key Data Encryption Now that Bob has a copy of the key, each time Alice needs to send him a message she starts by encrypting it using special encryption

software and the secret key. The encrypted message now looks like a jumble of random letters and numbers. Data Encryption Alice then sends the encrypted message to Bob. She can use a public network like the Internet, since, even if it gets

stolen, the encrypted message cannot be read or understood without the key. Data Encryption When Bob receives the message, he uses special decryption software and his copy of the secret key to decrypt the message. Bob can now read the original message from Alice.

Codes and Ciphers :: Caesar Cipher It is a Substitution Cipher that involves replacing each letter of the secret message with a different letter of the alphabet. Example : In this example, each letter in the plaintext message has been shifted 3 letters down in the alphabet.

Plaintext: This is a secret message Ciphertext: wklv lv d vhfuhw phvvdjh Codes and Ciphers :: Atbash Cipher The Atbash cipher is a very specific case of a substitution cipher where the letters of the alphabet are reversed. In otherwords, all As are replaced with Zs, all Bs are replaced with Ys, and so on.

Example Plaintext: Surabaya kota pahlawan Ciphertext: Hfizyzbz plgz kzsozdzm Codes and Ciphers :: Keyword Cipher The Keyword cipher is identical to the Caesar Cipher with the exception that the substitution alphabet used can be represented


To encipher a plaintext message, you convert all letters from the top row to their correspondng letter on the bottom row (A to K, B to E, etc). Codes and Ciphers :: Polybius Square Plain text : sekolah cita hati Cipher text : 43152534311123 13244411

23114424 Exercise : Crack the Code 2. 52231144 543445 431515 2443 52231144 543445 25333452 3. Key=7 : ilyzfbrbysho khsht zlnhsh ohs 4. Atbash : yvigvpfmozs wzozn wlz 5. Key = 3234454315

czoz cvizir yvkznzd lhwv Hints = tqe mromqc

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