Cryptography

Contents

Evolution of cryptography

Theory

Encryption and decryption

Data Encryption Standard

Public key cryptography

Symmetric key Cryptography

 

 

DATA ENCRYPTION STANDARD

 

The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES)

 are block cipher designs, which have been designated cryptography standards by the

US government.Despite its deprecation as an official standard, DES (especially its

still-approved and much more secure  tripple DES variant) remains quite popular;

it is used across a wide range of applications, from ATM encryption to e-mail privacy

 &.secure remote access.Many other block ciphers have been designed and released,

 with considerable variation in quality.Stream Ciphers, in contrast to the 'block' type,

create an arbitrarily long stream of key material, which is combined with the plaintext

bit-by-bit or character-by-character,In a stream cipher, the output stream is created

based on an internal state which changes as the cipher operates.That state's change is

controlled by the key,& in some stream ciphers,by the plaintext stream as well.

 RC4 is an example of a well-known stream cipher.

Cryptographic Hash Function”(often called message digest functions) do not necessarily use keys, but are a related and important class of cryptographic algorithms. They take input data (often an entire message), and output a short, fixed length hash and do so as a one-way function.

“Message Authentication Codes”(MACs) are much like cryptographic hash functions, except that a secret key is used to authenticate the hash value on receipt.

 

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