Review : Methods of Cryptography

. ABSTRACT: In order to safeguard the information and data that must be protected from any interference or incursion, security is one of the most significant and prominent concepts at the moment. There are several techniques to ensure security and the protection of our data, but cryptography is the most crucial. Because of the importance of the documents and information that institutions must deal with or transport over the Internet, where unauthorized users or hackers can read and manipulate them, these documents must be encrypted using cipher methods and techniques.


INTRODUCTION
The study and science of secret writing is known as cryptography.A cipher is a secretive writing technique in which plain text is transformed into cipher text.Decipherment, often known as "encryption", is the process of converting cipher text back into plain text.Encipherment, on the other hand, is the act of transforming plain text into cipher text.Cryptographic key(s) regulates both encryption and decryption [1].
Highly sensitive data will be encrypted in such a way that even if the data is taken by unauthorised parties, these parties will be unable to determine the true data since the data they steal is encrypted [2] .The original data to be conveyed is known as plaintext in cryptography, while the data that has been encoded is known as ciphertext.The goal of cryptography is to keep the information contained in data private so that unauthorised people cannot access it [3].

Symmetric Key Encryption
Up until the late 1970s, only symmetric encryption-also referred to as single key encryption, shared key encryption, or secret key cryptography-was employed.[5] .The sender and recipient of the communication could both have access to the secret key, or just one of them might.If two parties utilize private key cryptography to communicate secretly, each party must possess a copy of the secret key.[6] .The encrypted message can be easily deciphered by the attacker if the secret key has been compromised.This type of cryptographic technology must be used since it provides faster service without using a lot of resources [2].To date, different algorithms have been designed to explain symmetric key cipher.

Asymmetric Key Encryption
Public-key algorithms and, more generally, public-key cryptography are other names for asymmetric ciphers.With asymmetric ciphers, anyone can encrypt with the public encryption key (which could even be published in a newspaper), but only the intended recipient-who is aware of the decryption key-can unlock the message.The decryption key is often referred to as the private key or secret key, and the "encryption key" is known as the universal public key [7] .
The public key is made available to all entities, but the private key is kept hidden and never disclosed to any communication entities.Either a public key or a private key can be used to encrypt the data, depending on the security target (authentication or confidentiality) that the user wants to achieve [5].When the data is encrypted using the receiver's public key, confidentiality can be attained.Only the receiver has the necessary key to unlock the encrypted data.

Hash function
It carries the transformation by employing mathematics to permanently encrypt data.SHA-1, MD5, and more hash functions.[8].The hash function does not have keys as the ciphertext cannot be transformed to plaintext.

Substitution Techniques
The substitution technique systematically substitutes alternative letters or symbols for the plaintext's letters.Hill Cipher, Playfair Cipher, Monoalphabetic Cipher, Caesar Cipher, and Polyalphabetic Cipher are a few of the wellknown substitution ciphers.[9].

Cryptography Algorithms
In a cryptographic system, messages are encrypted and decrypted using sets of procedures or rules called cryptographic algorithms.They are techniques that protect data by preventing unauthorized users from accessing it, to put it simply .

Data Encryption Standard (DES) and Triple Data Encryption Standard (3DES)
IBM created the Data Encryption Standard (DES) in 1975, and the American National Standards Institute (ANSI) published a description of it in 1981 under the name ANSI X3.92.One of the most widely used symmetric key standards now in use is this one [11] [12].DES encrypts and decrypts data in 64-bit blocks using a 56-bit key.It accepts a 64-bit block of plaintext as input and outputs a 64-bit block of ciphertext, as seen in table 2. DES has 16 rounds, which means the core algorithm is executed 16 times to produce the ciphertext because it uses both permutations and substitutions and always operates on blocks of equal size.It has been found that the number of rounds in a brute-force attack causes the time required to find a key to grow exponentially.Therefore, as the number of rounds increases, the algorithm's security increases exponentially [12].Triple DES employs three separate keys, each with a

RSA
One of the first algorithms, it uses a public encryption key and a secret decryption key to function.The most widely used encryption method up to this point is RSA.RSA uses 1024 bit streams, which can currently also be up to 4096 bytes, for keying purposes.The primary characteristic of RSA is its reliance on huge prime integer values [13].The primary benefit of RSA is that its security is improved over other algorithms.It is actually one of the safest algorithms.The slow encryption performance, difficult key generation, and vulnerability to assaults are its main drawbacks.Making a public/private key combination, The three steps are: transforming plain text (data) into ciphertext (data), and decrypting the data to recover the original text [11] .

Diffie-Hellman (DH)
It is a protocol or technique that permits two cooperating entities to compute and exchange a key, then use this key in symmetric algorithms like AES [5].Benefits include security, a complex enough algorithm, and the fact that the secret key is never broadcast over a channel.However, due to the lack of verification, the method is unreliable, expensive, and inappropriate for the majority of encryption situations [11].

Conclusion
Because this data can be accessed by a third party or an outsider, security is critical in transmitting and dealing with it.Cryptography is essential for the secure transmission of data.Many techniques and algorithms are used to encrypt and decrypt data .
The speed of encryption and decryption, the accuracy of encryption, the complexity of the operations, the level of security, and other factors distinguish these techniques .