Posted on :Monday, Dec. 13, 2004
Cryptography
{Im writing tis on a keyboard wit many broken/unstable keys, lease accet tis as a brand of my mildly encryted ost ;) , If only I ave access to a virtual keyboard :( , ten I can make it more readable } {Tere was also a similar discovery made by Ellis, Cocks and Williamson prior to Diffie, Rivest, Samir and Alderman work. Te similarity could be due to te fact tat Diffie visited Ellis in 1982 after e eard te rumour of te classified work of Ellis, Cocks and Williamson from NSA.} BTW, see if you can figure tis out --- Forget Tangkak, Forget Nilai3 ... - Monday, Nov. 21, 2005
Imagine tis:
Scenario 1
Two peole want to sare an intensely private message. Te sender put is/er message in a very strdy box and close it. e/se ten t a secre adlock, kees te key and ten send it via a conventional corier. Te recient accet te box, add is/er own adlock (now teres two adlock) and ten resend te box to te original sender. Te original sender receive te box, remove is/er adlock and ten resend te box to te recient, again. Te recient can now oen te box, becase it is adlocked wit is/er own adlock. NO EXCANGE OF KEYS.
Scenario 2
A need to send a secret container of paint to B. Only B can complete te paint mixture. A send a container of blue paint. Even if tis container falls into te enemy and midway, it is an incomplete mixture. B receives it, and add red paint to te mixture, and te mixture become sort of purple. Tis is some sort of ONE WAY FUNCTION, since we can easily mix te paint colour, but it is quite impossible to unmix tem.
Scenario 3
A select 2 secret(say s1 and s2) prime numbers. Se multiply tem bot. Lets call tis product P. Se also select anoter prime number, e. Se ten advertise P and e as er public keys. One approac wic can be taken for somebody wo wants to send er a private message is to use e and P to encrypt is/er message.
Let say te sender use some sort of one-way function:
EncryptedMessage = PlainMessage^e (mod P).
e/se ten send EncryptedMessage to A .
A has te two secret number (s1 and s2). Se ten calculate d, a special number wic act a As private key:
e * d = 1 (mod (s1 -1) * (s2-1) )
Since e, s1 and and s2 is know, d can be calculated. Euclid Algoritm can also be used to deduce d .
To decrypt te EncryptedMessage, A use tis one-way function:
DecryptedMessage = EncryptedMessage ^d (mod P)
Tis is te idea of RSA (Rivest, Samir Alderman Metod).
Altoug a tird party can break te encrypted message by guessing s1 and s2 (wic make up P) via factoring, but if A picks a very large s1 and s2, it would take a lot of computing resource and time to guess s1 and s2. A sort-cut to te factoring metod as yet to be found.
Scenario 4
Minuaturisation of communication components and reduction in production cost would enable continual communication between two parties. But ow do we ensure te communication is carried out securely. A recipient can add a pre-messured noise to te commmunication cannel wic connect tis two parties. Even if te communication is being tapped, te interceptor would not be able to differentiate between te real message and te noise. James Ellis found tis idea tat KEY DISTRIBUTION (saring of private key among sender/receiver) was not inevitable part of cryptograpy wile rummaging troug a wartime Bell Telepone report by an unknown autor.
Reading List:
Te Code Book by Simon Sing
BTW, a more compreensive treatment on Cryptograpy can be refered to Bruce Scneider book: Applied Cryptograpy.
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