# Cryptography terminologies

Hi Everyone,

In this article, I will take you through common cryptography terminologies and what they mean. 

## Cipher
An encrypted message is called a cipher. Encryption techniques are helpful in maintaining **secrecy**.

Example: 
- Plaintext: *David is the traitor*
- Key: shift each letter by '2' letters in alphabetical order. ('a' becomes 'c')
- Cipher: *Fcxkf ku vjg vtckvqt*




## Encryption and Decryption
The process of converting 'readable' plaintext into a 'non-readable' ciphertext is called encryption, and the reverse process is called decryption.
![Encrypt_Decrypt_Diff_1.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1652689970387/-ZByBfN_X.png align="left")

A '**Key**'(data) is used to encrypt/decrypt.


There are 2 types of encryption algorithms:

**Symmetric-key algorithms**

- A single key is used for both the encryption of plaintext and decryption of ciphertext.
- Examples: DES(*Data Encryption Standard*), AES(*Advanced Encryption Standard*).

![symmetric-vs-asymmetric-symmetric-example.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1652708015028/mexUUmDAu.png align="left")

**Asymmetric-key algorithms (Public-key algorithms)**

- A pair of related keys(*Private and Public keys*) are used. One for encryption and the other for decryption. 
- The **public key** is out in the open for everyone to see. Whereas the **private key** must be kept secret and not shared with anyone. 
- If someone encrypts a message/plaintext using A's public key (available for everyone), only A can decrypt the ciphertext using A's private key.
- Similarly, If A encrypts a message/plaintext using his/her private key, anyone can decrypt the ciphertext using A's public key(available for everyone). 
- Examples: RSA(*Rivest Shamir Adleman*), ECC(*Elliptical Curve Cryptography*).

![Asymmetric-Encryption.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1652708674282/89keN9H61.png align="left")

*Symmetric-key algorithms are computationally faster than Asymmetric-key algorithms.*


## Hashing
Hashing is a one-way message digestion process of any varied-length input to a fixed-length output(*Hash/digest*). Hashing techniques are helpful in **validating data integrity**.

- It is one-way, as it is almost impossible to recover the original message from the hash value (unlike encryption algorithms, where cipher can be decrypted).
- Hashing algorithms are computationally super fast.
- *Deterministic*: meaning for a given input, the algorithm gives the same output every time it is run.
- *Avalanche effect*: Even a small change in the input drastically changes the output (hash value).
- A good hashing algorithm should withstand collisions. (since there will be collisions when larger varied length inputs are hashed to small fixed-length outputs EX:  (13 mod 9) = 4 and also (85 mod 9) = 4).
- Examples: MD5, SHA-1, SHA256

![academy-hashing-algo.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1652703873390/yEvdKy36t.png align="left")

*These properties are important in understanding why hashing plays a vital role in creating Blockchains*


## Digital Signatures
Just like signatures are helpful in verifying the authenticity, Digital signatures are useful in **verifying the authenticity** of the author/sender of the document/message. Hashing and Asymmetric-key(public key) algorithms are used in creating and verifying digital signatures.

**Sender(S):** 
- S wants to send Message(M) to the receiver(R). Hash of message(M) -> Hs is generated. 
- Hash(Hs) is encrypted(*Es-Hs*) using Sender's private key.
- Both (*Es-Hs* & M) are together encrypted(*Er-(Es-Hs & M)*) using Reciever's public key.

**Receiver(R):** 
- R decrypts the (*Er-(Es-Hs & M)*) using his/her private key. -> *Es-Hs* & M.
- R now generates a hash of message(M) -> Hr
- R decrypts (*Es-Hs*) using sender's public key -> Hs
- If (Hr == Hs) then, the sender's authenticity is verified.

![Digital-Signature-Illustration.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1652718663418/2PmeyyBo4.png align="left")

*Digital signatures are used in Blockchain networks. Wallets store private keys and the public keys(address) are shared over the blockchain network.*



## Homomorphic Encryption Algorithms
Homomorphic algorithms are helpful in implementing operations on the cipher and still achieve the result same as some operations performed on the plaintext and then encrypted. 

Example: 
- Say, A, and B are variables that store plain text. 
- Encryption Algorithm: Cipher of A be (g^A) and Cipher of B be (g^B).
- Decryption Algorithm: log(g^A) = A (base of log operation be 'g').
- On performing multiplication operation -> (g^A ) * (g^B) = (g^(A+B)) -> This is similar to perfoming addition (+) operation A and B and then encrypting it. 

*This feature is useful when the cipher is stored in a cloud environment (untrusted service providers can't view data) and the user can still perform operations without decrypting the cipher.*


## Salts, Nonces
These are one-time values used in cryptography that don't need to be secret but still lead to additional security.

**Salt**: Salt is used in password-based systems and is concatenated to the front of a password before processing, making it difficult for hackers to guess the password.
**Nonce**: *N*umber used *once*. A nonce is a random number, used in cryptographic protocols and algorithms, it should only be used a single time with any particular cryptographic key.





 
**Please do advise improvements and suggestions, helps me in making better content in the future. Thank you for reading. Have a great day.😎**