SECURITY and CRYPTOGRAPHY 15-827                  13-SEP-01
                        Lecture #1
       M.B.

       4615 Wean
                                                         cell:510 469-8730
My name: Manuel Blum  mblum@cs  W:268-3742 /\ office= WEAN 4113
Your TA: Nick Hopper  hopper@cs W:268-2993.  office = 8303 WEAN

WHERE I'M COMING FROM:
What can a Human do in his head?
What is consciousness?  (Why is sleep necessary?)
Why does our highly parallel brain have a serial bottleneck?
My approach to this is thru...  cryptography!

I WOULD LIKE THIS CLASS TO PUBLISH AN ORIGINAL RESEARCH PAPER 
IN A COMPLETELY NEW FIELD OF CRYPTOGRAPHY.
FOR THIS, I NEED YOUR HELP.

Give me a general rule for selecting a password.   
Suggestions anyone? 
 1.The lady at IBM suggests that you take a word from a dictionary 
and misspell it, eg capture > captcha
 2.Make up a sentence and use the first letter of every word. 
Bizarre sentences, being more memorable than most, are particularly good.

Suppose you have to change your password every month.
What would be a reasonable choice of passwd?  How about:
 3.January  -> kos      May    -> nzn    September -> tqu
    February -> gcs     June   -> kok    October   -> duc
    March    -> nsd     July   -> kmz     November  -> own
    April    -> qsm       August -> htu    December  -> edn

Another is:
 4.January  -> 729      May    -> 343    September -> 593
    February -> 489     June   -> 727    October   -> 638
    March    -> 396     July   -> 774      November  -> 263
    April    -> 997       August -> 653    December  -> 063

A HARDER PROBLEM: To what would you map   January 2001 -> ?

January 2002 -> ?

January 2003 -> ?

For example,                        January 2001 -> 496
                                          January 2002 -> 274
                                          January 2003 -> 507

The HumanOID Problem: To give a challenge-response protocol that is easy 
for any reasonably intelligent moderately literate 6 to 60 year old 
to authenticate himself but hard for an eavesdropper with a powerful 
computer to crack.

The PhonOID Problem: Same as HumanOID, except that challenge-response 
is done over the phone.


It is important to try also to prove that HumanOID/PhonOID protocols
are NOT possible. How?

1.Can a person make up a page of questions whose answers they alone 
are likely to know?  I think that YES, but I don't know how to do this yet.
Good sources of questions: family relationships.
                                         early memories.

2.MUCH HARDER PROBLEM: Can a person use the above info 
(the page of challenge-response pairs) as a seed to generate 
a virtually infinite number of challenge-response pairs? 
As usual:
*It must be easy for a person to respond to any challenge, 
doing all computations in his head. 
*It must be hard for an eavesdropper to crack the protocol.

A fundamental reason this appears to be hard is this: 
unlike computers, which can give each other their algorithms, 
the algorithms that humans learn are learned from observation. 
If a human is to learn a secret protocol for responding to a challenge, 
what's to keep eavesdroppers from learning, from observation of 
challenge-response pairs, how to respond to challenges?



BIRTHDAY PARADOX
QUESTION: In a world with n day per year, how many people should 
one invite to a party so that there is a roughly 50% chance that 
at least 2 people have the same birthday?
ANSWER: (1.2)*sqrt(n)


COUPON COLLECTORS PROBLEM
QUESTION: A cereal box contains one of n coupons, each coupon chosen 
uniformly at random (i.e. each coupon is equally likely to appear 
in a box). 
How many cereal boxes should one expect to buy in order to get all 
n coupons?
ANSWER: approximately n*(lg n).  
QUESTION: What base?

n/e   empty cells when you throw  n balls into  n cells.
n/e^2 empty cells when you throw 2n balls into  n cells.
n/e^(ln n) = 1                 (ln n)n  = 23    n = 10
n/e^(ln 2n) = 1/2             (ln 2n)n = 30     n = 10

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HOMEWORK #1: send email to nick.hopper@cs with a cc to mblum@cs.
Your email should include 2 challenge-response pairs for 
authenticating you.  Each pair should have the property that
you will long remember the correct response to the challenge.
You should be able to remember it exactly.

For example, 
Nick HOPPER:
CHALLENGE: What is the name of your 1st grade teacher?
RESPONSE:  "Miss Justin" or "Justin".

Abie FLAXMAN: 
CHALLENGE: What is the first CD you ever purchased?
RESPONSE:  

Pankaj ???:
CHALLENGE1: As a child, what cartoon did you most enjoy?
RESPONSE1:

CHALLENGE2: What was the registration # of your first motorcycle?
RESPONSE2:

Paul REITSMA:
CHALLENGE: What is the name of the first girl/boy that you
ever kissed?
RESPONSE: