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Types of Cryptography: Symmetric and Asymmetric
In this article, we are going to study the different types of cryptography. This article is merely about the classification of the cryptography. Let's just have a look at them and understand these different types.
Submitted by Monika Sharma, on January 17, 2020
Cryptography is a study of different techniques used for encryption and decryption of the text to convert the plain text into ciphertext and viceversa. There are many different cryptographic techniques and algorithm which have been developed so far.
These are broadly classified into two types,
 Symmetric key cryptography
 Asymmetric key cryptography
The sole difference between lies between the pair of keys used for encryption and decryption process.
1) Symmetric key cryptography
In the symmetric key cryptography, the same key is used for encryption as well as decryption. To maintain the security levels, this key is kept private so that no third party or unauthorized member can access the data.
There are further two types of symmetric key encryption techniques,

Substitution technique
In the substitution technique, the letters of the plain text are substituted by some other letters. This substitution is done with the help of a key and a suitable algorithm, and the decryption is also performed using the same key and just by reversion of the order of steps performed in the algorithm.
The substitution technique may also not be consistent throughout in all cases, i.e. the letter which is used for substituting any letter say 'm' at a position may or may not be the same letter for substituting 'm' at some different position of the plain text. According to this, there are 2 ways in which the substitution technique can be performed.

Monoalphabetic Cipher: Here, in this case, a single cipher alphabet for each plain text alphabet throughout the text.
Eg. If we are substituting 'm' by 'z', then this substitution will take place throughout the encryption process.
Example: Caeser cipher

Polyalphabetic Cipher: Here, in the case of a polyalphabetic cipher, no fixed cipher alphabet is used for substituting the plain text alphabets. Different alphabets can substitute the same alphabet of plain text at different places.
Eg. If we are substituting 'm' by 'z' at a place, then it may happen that 'm' is being substituted by some other letter say 'y' at some other place.
Example: Playfair cipher

Transposition technique
The transposition technique includes performing some sort of permutation on the plain text letters. It should be noted that the length of plain text and cipher text remains the same in this technique.
Eg. 'NAME' can be encrypted as 'MNAE' or 'EANM' etc.
Examples: Railfence cipher
2) Asymmetric key cryptography
In the asymmetric key cryptography, a pair of different keys are used for encryption and decryption process. Usually, one of these keys is kept public, i.e. which is made available to all and the other is kept private, i.e. is available only to the authorized members. To maintain confidentiality and authentication, it is a convention that the encryption is done by the public key and the decryption with the help of the private key.
Examples: Diffie Hellman Cipher, Elliptic curve cryptography
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