compression in images via motion estimation and diffs between images
motion est is key to exploiting temporal correlations
most complex component in video compression system
in std techniques, only translations considered because of complexity
more accurate ME with rotation and scaling leads to better temporal redundancy reduction, thus improved compression efficiency, but with higher complexity
mpeg motion picture expert group
	lossy video compression
	first approx: jpeg on each frame
	also removes interframe redundancy
video encoder
	ME done
	interframe correlation done
video decoder
	ME not performed at decoder
	interframe correlation exploitation mainly at encoder

crypto
	study of means of converting info form normal form into an incomprehensible format, unreadable without secret knowledge
	intro
	algorithms
	auth protocols

security services
	privacy - preventing unauthorized release of info
	auth - verifying ident of remote participant
	integrity - making sure message has not been altered
	
terms
	encryption
	plaintext
	ciphertext
	decryption
	cipher - algorithm(s) for enc and dec
	key - used with cipher

DES - uses a key for enc and dec
enc functions
	symmetric key
		block cipher
			DES - data encryption standard using DEA
				64bit - 56bit key+8bit parity
			3DES - 168bit key
			AES - advanced encryption standard

randomness generated from a IV (initiation vector)

openssl enc -aes-256-cbc -d -a -out ...

public key enc
can send public key over insecure channel, everyone needs to know it
algorithms usually based on hard math problems
provides mechanisms for digital sigs
examples: rsa, ecc, dsa, eigamal

rsa
	choose two large primes, each 256 bits
	mult them to get n
	choose enc key e such that e and (p-1)x(q-1) are relatively prime
	compute dec key

public key pros
	solves prob of passing key
	allows est of trust context between parties
weakness
	slow
	problem of trusting public key

hashing functions
	transofrmation that takes variable sized input and outputs fixed size
	main role of crypto function is in provision of digital sig
	for digital sig apps where a large message has to be compressed in a secure manner before being signed with the private key
	notables: md5, sha1