Cryptography is the technique which are used widely that allow the user to encrypt the data or information so that data hiding or information hiding can be possible. Cryptography is a science which converts plaintext into ciphertext.

Cryptography includes various methods of sending messages in hidden form such that the authorized recipients only can find the hidden disguise and read the message.

It is the art of converting data in such a way that the data can only be accessed by the authorized persons who have the ‘key’ to access.

### Basic Terminologies

- Cipher: It is the functionality that does the encryption.
- Cipher-text: This message has been changed such that it cannot be read by any person who’ll try to read it. That message only can be read by the person who is having the key.
- Decryption: In this process, the cipher-text will be converted back to the original text to read the message.
- Encryption: In this process the message or data will be scrabbled by using the various algorithms available in all cryptographic algorithms.
- Key: It is the code which is useful to control the operation and the behavior used during the application of the cryptographic algorithm.
- Plaintext: It is a message or data which is available in its pure natural form which is to be read by the attacker.
- A digital signature: It is a group of data or information which is created by the sender of a message by using secret key.

## TYPES OF CYRPTOGRAPHY

## SYMMETRIC KEY CRYPTOGRAPHY

In Symmetric key Cryptography, the single key is used to encrypt or decrypt the data. The key which is transferred to the receiver end to decrypt the data, is the same key from which the data is encrypted. So, this type of cryptography is also called as similar key cryptography. IT is the easiest and fastest type of cryptography.

Examples:

**AES**, DES, Caesar Cipher

ADAVANTAGES OF SYMMETRIC KEY CRYPTOGRAPHY

- Much Faster type of cryptography
- Less intensive

DISADAVANTAGES OF SYMMETRIC KEY CRYPTOGRAPHY

• Necessity of secure mechanism to deliver keys properly.

• Provides confidentiality but not authenticity or nonrepudiation

## ASYMMETRIC KEY CRYPTOGRAPHY

In asymmetric key cryptography, two different keys are used to encrypt or decrypt the data. One key is used to encrypt the data, and other one is used to decrypt the data. Here the most important thing that we have to note is here “the keys are different but they are related to each other”. The two different keys are used in asymmetric key cryptography:

PUBLIC KEY: the public key is used to encrypt the data i.e. the plain text is converted into cipher text with the use of public key. Public key is shared by anyone and can be derived from private key.

PRIVATE KEY: the private key is used to decrypt the cipher data into plain text. This key should not be shared with anyone.

Examples:

- ECC
- Diffie-Hellman
- DSS

*Advantages of Asymmetric Key Cryptography*

- Better key distribution than symmetric systems.
- Better scalability than symmetric systems
- Can provide authentication and nonrepudiation

*Disadvantages of Asymmetric Key Cryptography*

- Works more slowly than symmetric systems
- Mathematically intensive tasks
- High complexity

## HASH FUNCTIONS

The types described above has some problems. It is slow, and it produces a large volume of data. An improvement to the above type is the addition of a one-way hash function. The functionality of hash function is that, if the information is changes, the entire hash value changes.

Hash function convert the variable length plain text into fixed length alphanumeric function. It is irreversible, many operating system uses this method to store the passwords.

Some of the hashing algorithms are:

MD5, **SHA-1**__, SHA-256 etc.__

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