Encryption

Encryption

1. Symmetric Encryption

   • oldest and best-known technique
     • Also known as Shared or Secret Key Encryption
       • Uses a shared secret key Ks to encrypt a message, M. If Ciphertext = Ks(M)‏ Then M = Ks(Ciphertext)‏
         • Uses a shared secret key Ks to encrypt a message, M. If Ciphertext = Ks(M)‏                 Then M = Ks(Ciphertext)‏
       • Requires a key distribution service - The Trusted Third Party
       • Example is Data Encryption Standard (DES), developed for US DoD.
   • A secret key, which can be a number a word, or just a string of random letters
     • is applied to the text of a message to change the content in a particular way.
       • This might be as simple as shifting each letter by a number of places in the alphabet
   • faster 100 to 1,000 times than public key encryption
     • provide secrecy for the bulk encryption and decryption of information.
       • used by security protocols as session keys for confidential online communications
         • Transport Layer Security (TLS) and Internet Protocol security (IPSec) protocols use symmetric session keys with standard encryption algorithms to encrypt and decrypt confidential communications between parties
         • Different session keys are used for each confidential communication session and session keys are sometimes renewed at specified intervals.

2. Asymmetric Encryption

   • Asymmetric cryptography or public-key cryptography
     • pair of keys is used to encrypt and decrypt a message so that it arrives securely
     • A network user receives a public and private key pair from a certificate authority.
     • Asymmetric Uses a key-pair - two different keys
       • one private, Kpriv - for decryption
       • one public, Kpub - for encryptionM = Kpriv( Kpub(M))‏
   • Key pairs based on factors of prime numbers
     • Difficult to calculate effective key pairs
       • Extremely difficult to crack (billions of years)‏
       • Slower in operation than DES (100-10,000 times)‏
       • Provides a signature that cannot be reproduced
       • Keys for commercial level security are 1024 bits long and are typically 1024–2048 bits long