Encryption 2

Encryption 2

1. Hashing

   • Storing passwords in plaintext is a BIG security risk
     • Anyone who gains access to the database could potentially see all of the passwords
   • An algorithm is used when you enter your password and "hashes it"
     • Returns a difficult to understand string
       • e.g. 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
       • This hash is then stored in the servers
     • The output will change dramatically from even the slightest change
     • When you enter your password, the site checks the hash of your password against the hash it has stored
       • If they match, you can log in
     • The site cannot decipher the hash back into your password
       • Therefore, it will allow you to change your password when you have forgotten it
         • They don't actually know your password!

2. Vernam's Cipher

   • Developed by Gilbert Sandford Vernam in 1917
   • Only truly unbreakable cipher
     • Security of the cipher is completely reliant on the pad
   • Symmetrical stream cipher
     • Text is combined with random data of the same length
     • Similar to Enigma
   • Cipher text is generated using an XOR
     • XOR = "Exclusive OR"
     • Outputs 1 when the values are different
     • Outputs 0 is the values are the same
     • 11 = 0
     • 10 = 1
     • 01 = 1
     • 00 = 0
     • If you perform an XOR on the encrypted text with the key, you can retrieve the original message
   • Random cipher pad is produced
     • Copy of pad is given to each recipient of the message
       • Sender uses pad to encrypt plaintext
         • Recipient can use pad to decrypt message
   • Uses of the cipher
     • Used by the Germans to transmit messages during WWII
     • Also used by undercover Russian agents to send messages
     • Theoretically this is 100% secure
       • Any attempt at bruteforcing could result in almost any message
     • Security is reliant on cipher pad
       • If you use it more than once, cryptanalysis can be perfomed
       • Pad MUST be completely randomly generated and be as long as/longer than the actual message
         • Recurring patterns could mean the key can be figured out

3. Vigenère Cipher

   • Polyalphabetic substitution
     • Each letter can represent more than one letter
       • e.g. a could = g or n
   • We use a "tabula recta" to replace each letter in accordance with the keyword
   • Was originally thought to be unbreakable
     • We can use a mathematical formula called Kasiski's analysis to determine the length of the keyword

4. Cryptanalysis

   • Technique of analysing ciphers to discover their meaning
     • Often this can be done through knowing a portion of the deciphered text and comparing it with the ciphertext
       • German messages in WWII were able to be decoded much easier, since almost all ended with "Heil Hitler"
     • Repetitions in the cipher can help to determine possible key-lengths
   • Ciphers that use non-random keys are vulnerable to attack and can be solved with enough time and resources
     • Even computer-generated random values are not truly secure
       • "Pseudorandom"
       • Computer has a very long array in which "random" values are picked
       • Computers cannot generate random numbers
     • A truly random key must be used with the Vernam Cipher to ensure it is mathematically impossible to break