## Encryption

- The privacy can be achieved using encryption / decryption methods.
- There are two types of crypto system or Two categories of encryption/decryption:

– Secret key

– Public key

Secrete/Private key cryptography

Refers to symmetric cryptography , the same key is used for both encryption & decryption . The key must be known to both sender & receiver location . Secrete/Private key cryptography is also called as conventional cryptography

- The basic principle in
**Symmetric Key Cryptography**is the that both the parties involved in the communication must agree on the encryption key in advance. This means that both parties use the same key, which must, under all circumstances, be kept secret.

- Symmetric-key algorithms can be separated into stream ciphers and block ciphers
**.**In**.”**

- Symmetric-key algorithms are usually much faster to use electronically than asymmetric key algorithms.

** Important symmetric key cryptographic algorithm**

The most popular secret key crypto-system in today’s known as **DES (**Data Encryption Standards are most widely used encryption standard.), **IDEA**(International Data Encryption Standards) ,**RC4 **(Rivest Cipher 4), **RC5 , Blowfish**

**Limitations of secret key**

- The first problem is that Key agreement or key distribution (we can send the key is to courier a paper on which key is written, but not convenient .second way send key over n/w & ask for confirmation )
- Same key is get used for encryption & decryption . If ‘A’ wants to securely communicate with ‘B’ & ‘C’ then their must be two separate keys.
- Since keys are subject to discovery, they need to be changed often and kept secure during use. Key exchange is a huge problem, since the confidentiality of the message relies upon the secrecy of the key.

**Public key cryptography **–

Each user has public key & private key . Public key is made public while private key remains secret. Encryption is performed with public key & decryption is done with private key . (you encrypt the message using the recipients public key & decrypt that by using your own private key.)

Public key cryptography is also called as “ asymmetric cryptography”

The **RSA** public key cryptosystem is most popular form of public key cryptography . RSA stands for Rivest, Shamir & Adleman the inventors of RSA cryptosystem.