## 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 block ciphers clear text into fixed-length blocks and then proceed to encrypt those blocks into fixed-length ciphers. stream ciphers work on information “bit-by-bit” rather than “block-by-block.”

• 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.

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