The art of protecting information by transforming into an unreadable format is known as Cryptography.

- Coding Skill के उपयोग के माध्यम से सूचना और संचार की रक्षा करने का तरीका ताकि केवल उन लोगों को जानकारी की आवश्यकता हो जो इसे पढ़ सकते हैं और इसे Cryptography कह सकते हैं।
- Cryptography प्रोटोकॉल का निर्माण और विश्लेषण करने के बारे में है जो तीसरे पक्ष या जनता को निजी संदेशों को पढ़ने से रोकता है।
- Secret Writing का विज्ञान एक प्राचीन कला है|क्रिप्टोग्राफ़ी का पहला Documented उपयोग लगभग 1900 वर्ष पहले एक मिस्र के मुंशी ने एक शिलालेख में गैर-मानक चित्रलिपि का उपयोग किया।

**Privacy / Confidentiality:** Ensuring that no message can be read except to the intended receiver.**Authentication:** The process of proving one’s identity.**Integrity:** Assuring the receiver that the received message has not been changed from the original in any way.**Non-repudiation:** A mechanism to prove that the sender has actually sent this message.**Key Exchange: **The method by which a crypto key is shared between the sender and receiver.

## Encryption

Encryption is a process in which the data or information sent by the sender is encoded using an encoding algorithm to fail to read it when accessed by any hacker or third party.

## Decryption

Decryption is a process in which the data or information sent by the sender is decoded using any decoding algorithm so that it is readable after the receiver receives the data or information.

## Key

1.A string of bits used by **Cryptography** algorithms to transform plain text into ciphertext or vice versa.

2.It is used for secure communication.

### Types of Key

#### Symmetric key

1.RC5 is a symmetric key block encryption algorithm developed by Ron Rivest. It is an encryption system where the sender and receiver of messages use a single common key to encrypt and decrypt messages. Symmetric key systems are fast and simple, but the problem is that the sender and receiver must somehow exchange the keys in a secure manner. The most popular symmetric-key cryptography system is the Data Encryption System.

2.Symmetric-key cryptography is a means of encrypting data or information in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but easily related in a computational way). It was the only publicly known type of encryption until June 1976.

3.Symmetric key ciphers are implemented as either block ciphers or stream ciphers. A block cipher blocks flat input in plain characters as opposed to individual characters, the input form used by the stream cipher.

4.Symmetric-key cryptocurrencies use the same key for encryption and decryption of a message, although the message or group of messages may have a different key than the others. A significant disadvantage of symmetric ciphers is the key management required to use them safely.

#### Asymmetric Key Cryptography

Under this system, a pair of keys are used to encrypt and decrypt information. A public key is used for encryption of data and a private key is used for decryption of data. The public key and private key are different. Even if the public key is known by all, the intended receiver

can only decode it, because he alone knows the private key.

#### Public-key Cryptography

1.In public-key cryptosystems, the public key can be freely distributed, while its paired private key must remain secret. The public key is used in the public-key encryption system for encryption,

while the private or secret key is used for decryption.

2.Public-key cryptography is also used to implement digital signature schemes.

3.Digital signatures may also be permanently attached to the content of the message being signed; They cannot then be ‘transferred’ from one document to another, traceable to any attempt.

4.DSA and RSA are both of the most popular digital signature schemes.