acg tips

From Yong Xiang:
- C.I.A (Classical Security Objectives)
- Cryptanalytic attacks.
- Confusion - Permutation /diffusion -

- Classical Cipher
-Caesar (+3,-3) 26 letters
- Playfair (5X5) 36X26 letters/combinations
-Improved security
-Need a 676 entry frequency table to analyse
-The ciphertext depends on diagraph pair
-Reepated digraphs produce same ciphertext each time.
-Decipherment based on digraphs much more diffucult.(NOT IMPOSSIBLE NOW)

-Vigenere (table 26X26) That big table
-Rail Fence up down the alternating letters then take the ciphertext from first and second line.

-STRENGHT OF CIPHERS
-Good ciphers?
-Amount of secrecy needed should determine effort to encrypt and decrypt.
-key set and enciphering algorithm should not be complex.
-Implementation should be as simple as possible
-Errors should not propogate.
-Symetric Algorithm
-DES (64bit block, 56 bit KEY)
-ECB/CBC/CGB.OFB
-How they work?
-Trple DES 3DES
112 and 168 bit key.
-168 bit key (3keys)
-Encryption (E-D-E) 1st 2nd 3rd Key.
-Decryption (D-E-D) 3rd 2nd 1st key

-112-bit key
-Encryption (E-D-E) 1st 2nd 1st key
-Decryption (D-E-D) 1st 2nd 1st Key
-Asymetric
-RSA
- Public Key and Private Key.
-Calculations
c= M to the power of e mod n (pxq)
M = c to the power of d mod n (pXq)

One way hash function
-Message Digest
-One way
-Collision Free
-Fixed length of output
-Examples?
MD4/5, SHA 1,256,512.
Message Authentication code
-Key Hash Function
- Ewquires a secret key
Examples
(need to know)

-Key Distribution issue in symetric key distribution. Key can be lost, forgotten, forged.
-Public Key Infrastructure
-Problems or issues of PKI
-Authentication
-One Way (UserID and password)
-Two way/Mutual (Challenge Response Protocol)
-A Nonce (challenge) to B. Usually encrypted with password.
-B Nonce (message) to A.
-Compare results.
(THIS IS ONLY AN OVERVIEW) WHY NEED TWO WAY?
-Kerberos
-AS
-TGS
-Users subsequently request access to other services from TGS.

-Key exchange protocols
-RSA (public key to encrypt.) need PKI
-Fixed Diffie Hellman (need PKI)
-Anonymous Diffie Hellman (Exchange public parameters.With it and random number to generate a common value.)
-Ephemeral Difie Hellman (need PKI)
-Fortezza
Common value is not secret key. Use it for key exchange, Diffie hellman use to get that common value. So the key won't be seen!

(Need to know)
-IPSec
-SA
-How it works
-Applications
-SSL
-Suite of Protocols
-How it works?
-Applications
-SET
-Suite of protocols
-How it works?
-Applications

Also read on lectures slides, all tutorial exercises for better knowledge.

from Koon Ming: