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Cipher MethodsThere are 2 methods of encrypting plaintext:• Bit stream method – every bit in the plaintext bit is transformed into a cipher bit one bit at a time.• Block cipher method – the message is divided into blocks (for example sets of 8-, 16- or32-bit blocks) and then each block of plaintext is transformed into an encrypted block of cipher bits by using an algorithm and a key.Bit stream method which is uses algorithm functions like XOR, while block cipher method can use substitution, transposition, XOR, etc.Substitution cipherSubstitution cipher substitutes one value for the other value. The following are the different types of substitution:• Monoalphabetic substitution – It uses one alphabet to substitute. Simple method but powerful if combines with other operations.• Polyalphabetic substitution – It is more advanced method which uses two or more alphabets.• Vigenère cipher – It is an advanced type of cipher which uses simple polyalphabetic code that is made up of 26 distinct cipher alphabets.Transposition cipherTransposition cipher rearranges values within the block to create ciphertext.Exclusive OR (XOR)It is a function of Boolean algebra where the two bits are compared to each other• If the two bits are identical, result is 0• If the two bits not identical, result is 1Vernam cipherThis is developed at AT&T that uses set of characters once per encryption process.Book (or Running Key) cipherThis method uses text in book as key to decrypt a message where ciphertext contains codes which represents page, line and word numbersHash FunctionsHash functions are mathematical algorithms that generate message summary or digest to confirm message identity and confirm no content has changed. Hash algorithms are publicly known functions that create hash value. Use of keys is not needed, but message authentication code (MAC) may be attached to a message. This method is mostly used in password verification systems to confirm identity of user.
Techniques for combating Spam mails Many anti spam products are commercially available in market. But it should also be noted that no one technique is a complete solution to
IP DATAGRAM SIZE: Datagrams may have different sizes i.e. Header area is generally fixed (20 octets) but can have various options. Data area may contain between 1 octet and 6
Question: a. State briefly three reasons why computer networks are used? b. Differentiate between simplex, half-duplex and full-duplex mode of transmission. c. State any
Ask You have been asked by a new client to assist in setting up a new computer for her coffee shop. She has just purchased the newest Apple computer from an online site. Should wou
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Asymmetric Encryption Asymmetric encryption method makes use of two different but related keys and either key can be used to encrypt or decrypt the message. This method is freque
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Question: (a) What are the various options to mitigate risks in an Information Security Management System (ISMS)? For each option specify an instance where it can be used.
- Alice, Bob and Charlie have a secret key a=3, b=4, c=5, in that order. - They would like to find a common secret key using Diffie-Hellan key exchange protocol (with g=2, p=5).
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