'Crypto' is Greek for 'hidden' or 'secret'. The science of writing in secret to keep data hidden is known as cryptography. On the other side, cryptoanalysis is the study of how to crack cryptosystems, sometimes as an art. Each of these expressions falls under the umbrella of cryptology. Cryptography is an important aspect when we deal with network security.

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Symmetric and asymmetric cryptography are the two main categories of cryptography. The descriptions of these categories are provided below:

• Symmetric key cryptography helps to secure the message's contents by combining one secret key with encryption and decoding procedures. The quantity of key bits affects how secure symmetric key cryptography is. Compared to asymmetric key cryptography, it moves more quickly. As the key must be sent across a secure route from the sender to the recipient, a key distribution issue occurs.

• Asymmetric key cryptography is sometimes known as public-key cryptography because it uses both a public key and a secret key. As both parties utilize distinct keys for encryption and decryption, it resolves the key distribution issue. Due to its extreme slowness when compared to symmetric key cryptography, it is not practical to employ for decrypting mass communications.

• Hashing: This process entails taking plain text and using a hash function to transform it into a fixed-size hash value. As the hash value on both the sender's and receiver's sides should match if the message is unchanged, this method assures the message's integrity.

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Techniques for Cryptography

In the era of computers, cryptography is frequently connected with the transformation of plain text into cipher text, which is text that can only be decoded by the intended recipient. This process is known as encryption. Decryption is the process of converting encrypted text into plain text.

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The following list of cryptographic features:

• Information may only be viewed by the intended recipient and no one else. This is known as confidentiality.

• Information cannot be changed while being stored or sent between a sender and the intended recipient without the addition of new information being noticed.

• Non-repudiation: The information creator/sender is unable to subsequently retract his desire to disseminate information.

• Authentication: The sender's and receiver's identities are verified. Additionally, the information's origin and destination are verified.

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Hill Cipher

A polygraphic substitution cipher built on linear algebra is the Hill cipher. A number modulo 26 represents each letter. It is common to employ the straightforward formula A = 0, B = 1,..., Z = 25, however, this is not a necessary component of the encryption. Each block of n letters, which is thought of as an n-component vector, is multiplied by an invertible n n matrix against modulus 26 to encrypt a message. Each block is multiplied by the inverse of the encryption matrix to decrypt the message.
The set of invertible n n matrices should contain the cipher key, which is the matrix used for encryption (modulo 26).

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Vigenere Cipher

A technique for encrypting alphabetic text is the Vigenere Cipher. It employs a straightforward method of polyalphabetic substitution. Any substitution-based encryption that employs numerous substitution alphabets is referred to as a polyalphabetic cipher. The Vigenère square or Vigenère table is used to encrypt the source text.

The table contains the 26 possible Caesar Ciphers written out 26 times in various rows, with each alphabet shifting cyclically to the left in comparison to the previous alphabet.
The cipher switches to an alphabet from one of the rows at various stages of the encryption process.
Each point's alphabet is determined by a keyword that appears repeatedly.

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Caesar's Cipher

One of the earliest and most basic encryption techniques is the Caesar Cipher. It is merely a sort of substitution cipher in which each letter of a given text is substituted with a letter that is located a certain number of positions farther down the alphabet. As an illustration, if there was a shift of 1, A would be replaced by B, B by C, and so on. Julius Caesar, who reportedly employed it to communicate with his officials, is said to be the inspiration for the method's moniker.

Therefore, to cipher a given text, we require an integer value, or "shift," that represents the number of positions down which each letter in the text has been moved. Modular arithmetic can be used to express the encryption by first converting the letters' letters into numbers, where A = 0, B = 1,..., and Z = 25. Mathematically, encrypting a letter with a shift n is expressed as.

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Keyword Cipher

Monoalphabetic substitution is used in keyword ciphers. The letter matchings of the cipher alphabet to the plain alphabet are determined using a keyword as the key. After removing letter repetitions from the word, the cipher alphabet is created by matching the keyword to the letters A, B, C, etc. until the keyword is exhausted. Thereafter, the remaining ciphertext letters are used in alphabetical sequence, omitting those that have already been used in the key.