# FUNDAMENTALS OF COMPUTER

## COMPUTER THREATS SECURITY

### TYPES OF NETWORK SECURITY

 Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
A method of encryption and decryption in which each letter in the alphabet is replaced by another.
 A encryption B decryption C substitution cypher D plaintext
Explanation:

Detailed explanation-1: -Substitution Ciphers. Substitution ciphers encrypt the plaintext by swapping each letter or symbol in the plaintext by a different symbol as directed by the key. Perhaps the simplest substitution cipher is the Caesar cipher, named after the man who used it.

Detailed explanation-2: -In cryptography, a substitution cipher is a method of encrypting in which units of plaintext are replaced with the ciphertext, in a defined manner, with the help of a key; the “units” may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth.

Detailed explanation-3: -substitution cipher, data encryption scheme in which units of the plaintext (generally single letters or pairs of letters of ordinary text) are replaced with other symbols or groups of symbols.

Detailed explanation-4: -A shift cipher involves replacing each letter in the message by a letter that is some fixed number of positions further along in the alphabet.

Detailed explanation-5: -A substitution cipher replaces each letter in the message with a different letter, following some established mapping. A simple example of a substitution cipher is called the Caesar cipher, sometimes called a shift cipher.

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