Key encryption

Key encryption

1. Asymmetric

   • has 2 keys
     • Private key
       • Private
     • Public key
       • Shared
   • Examples?
     • Pretty good privacy (PGP)
       • Program
       • private key
         • Algoritm?
           • AES
           • Tripple DES
           • IDEA
           • CAST
           • Twofish
       • public key
         • Algoritm?
           • RSA
             • Combine 2 large prime numbers
             • In it self is one of the first implementations of a asymmetric crypto system
             • Very slow compared to symmetric crypto algoritms
       • Hybrid crypto system
         • The public key is encrypted using a asymmetric crypto algoritm
         • Privare cipher is encrypted/decrypted using a symmetric crypto algoritm
   • Also known as public-key encryption
   • Common use?
     • Browser <-> Webserver
     • VPN
     • SSH/SFTP
   • Slower then symmetric
   • Potential attacks?

2. ·

3. Symmetric

   • Examples?
     • AES (Advanced Encryption Standard)
       • block-type
         • 256-bit
         • 128-bit
         • 192-bit
       • Cryptotype?
         • Substitution
         • Permutation
       • Still in use
     • DES (Data encryption Standard)
       • Block type
         • 64-bit
         • 56-bit
       • Considered weak. Replaced by AES.
       • Cryptotype?
         • Permutation
         • Substitution
   • Has 1 key
   • Also known as private-key encryption
   • Ciphers?
     • Blockcipher
       • Fixed blocksize
         • Often 64- or 128-bit blocks
       • Fixed size
         • Usually 64- or 128-bit
     • Streamcipher
       • encrypts bits or blocks
       • Very fast
       • Key is combined with a initialization vector (IV)
         • The IV should never be the same
       • Very fast
       • One bit or byte at the time
   • Fast
   • Weakness?
     • Potential attacks
       • Known plaintext attack
       • Chosen plaintext attacks
       • Differential cryptoanylisis
   • D(K,Y)
     • Symmetric decryption of ciphertext Y using secret key K

4. Hash

   • H(X)
     • Hash function of message X