Encyption

Encyption

1. Symmetric Key Encryption

   • Encryption and decryption keys are the same
     • Parties communicating must agree on a secret key
       • Only they both know the key
         • The recipient can decrypt the message using the key
   • Fast algorithms exists so can use large keys making it harder to crack
     • need another secure channel in order to give recipient the key
       • if one person need to communicate with many people each person needs a different secret key from the rest

2. Public Key Encryption

   • The encryption key is made public
     • Anyone can use the public key to encrypt messages
       • Decryption is done using a different key which is secret
         • Only the receiving person has access to the decryption key
           • Nobody but owner of the key can decrypt
   • PGP - Public Key Encryption
     • Sender Generates a random Session Key (never used again)
       • Session Key used to encrypt message
         • Session Key itself is encrypted using recipients public key
           • Both encrypted message and encrypted session key sent to recipient
             • Recipient uses private key to decrypt Session key
               • Session key then used to decrypt message

3. Caesar Cypher

   • Short cypher, shifts alphabet places in desired direction depending on key given
     • not secure, but effective
       • Can be used within other encodings (which are secure)

4. Vigenère Cypher

   • 26 shifts in a table
     • Each row of the table is denoted by a letter of the alphabet
       • Password known only to sender and recipient.
         • repeated letters are not encoded in the same way so cannot be spotted in the decryption