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					Group based key
Adv – scales, adding new nodes, remove nodes                                    IMAP – 143/tcp
Disadv – only need one sensor                                                   Online and offline operation
                                                                                Leave copy on server
Pair-wise key                                                                   Multiple clients access same mailbox
Adv – need to compromise a lot of sensors                                       Support encrypted login
Disadv – doesn’t scale, hard to add/remove                                      Access to mime parts and partial fetch
                                                                                Message state information
Probabilistic key                                                               Create directory in mailbox
Have a large pool, take out certain amount, probability of X% they will share   Server side search
one key                                                                         Search algorithm on server consume resources
                                                                                Complexity of software
Derive probability                                                              Keeps user state across sessions
((n-m)!)^2 / ((n-2m)!n!); n – pool size, m – keys chosen
                                                                                Email to multiple receivers, efficient confidentiality
                                                                                Use symmetric key to encrypte message
                                                                                Encrypt symmetric key with public key

                                                                                Onion routing
                                                                                Acts like envelope wrapped in another envelope so that each node only
                                                                                knows who they’re receiving from and who their sending to. Message is
                                                                                encrypted and is re-encrypted at each node including only the instructions
link node identities to keys                                                    for where to send next.
adv – easier for sensors to find matching keys
disadv – easier for attacker to figure out which sensors to compromise          Proxy
                                                                                Sends on behalf of original sender, relays server responses back to sender
q-composite                                                                     Sender terminates smtp connection at proxy, proxy builds new connection to
must share at q keys; new key made from all shared keys                         actual destination
                                                                                No store-and-forward
establish link key from multipaths, random numbers for each path                Possible attacks
key xor’ed with each random number for each path                                Spoofing
basic approach vs q-composite q =1                                              Replay
basic approach only use one of the shared keys                                  Attacks on mail access prots
q-composite xor’s all shared keys                                               DoS
                                                                                Traffic analysis
polynomial bi-variate
f(x,y) = f(y,x); t-degree polynomial                                            Email secure
every sensor i, new polynomial f(i,y)                                           Spoof/replay – digital signature w/ 1-way hash, timestamps
need t+1 nodes to figure out poly formula                                       Eavesdropping – encryption (L4/7); PEM/PGP/S/MIME
                                                                                Prevent attacks on prots – SSL
MTAs                                                                            Other attacks – general network security problems (DoS)
Adaptable to temp network partitions                                            PGP – personal
Easy form chain of trust                                                        S/MIME – commercial
Easy impl traffic control
Easy conn part. Networks diff prots                                             Comments to avoid spam detection
                                                                                V<!-- banana -->i<!-- wumpus -->a<!-- dinosaur -->g<!-- potato -->r<!-- amtrak
Local exploder                                                                  -->a
Easy to prevent mail forwarding loops
Easy sender avoid sending multiple copies to same user                          Invisible ink
Easier to handle billing issues                                                 Use html/css to write large paragraph and make font very similar in color to
                                                                                background to only the intended message is easy to read
Remote exploder
Send to unknown users in list                                                   Bayesian filtering
Reduce traffic from users                                                       After trained, measures the probability of a token being found in spam or ham
Multiple lists; improve efficiency                                              and measures a score based on observed tokens in future emails

MIME                                                                            CRM114
Additional lines in header                                                      Uses sliding window to make up phrases to compare instead of a single word.
MIME Version
Method used to encode data
Multimedia data type, subtype, parameter declaration
Encoded data
Boundary parameter to separate parts

POP3 – 110/tcp
Work on temp network conn, view/edit offline
Retrieve/delete from server
POP3 UIDL can leave copy
String chars instead of nums to represent email
Support encryption thru SSL/TLS
Cmds – user, pass, list, retr, dele, quit
Stateless across sessions
Create folders; not possible for same view multi-pc

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