View Full Version : a newb ie question?

October 28th, 2001, 15:09
Anyone can enlighten us on simple XOR encyrption and other simple encryprion schemes?

October 29th, 2001, 10:20
I (wrongly, maybe) guess that the Eternal Loser question deserves a deeper answer, because it seems that he/she wants to know more about general, theoretical principles, and not only about the strength of the related algorithms.
Beside, from a theoretical point of view, the XOR-based algorithms are anything but weak; on the contrary, XOR-based algorithms are theoretically inviolable. This principle was stated in 1917 by Gilbert Vernam; he demonstrated that a text ciphered by XORing with a random-generated key (the "worm" never can be deciphered, provided that the text and the key are the same size.

From a practical point of view, the system (as is, at least) is useless. Sending to the recipient two texts of the same size is equivalent to duplicating the amount of information and simply halving the risks.

So, in practice, more "handy" worms are builded up by multiplying two primes L1 & L2; in this way, the sequence will show a L1xL2 periodicity (allowing the use of the methods described by ArthaXerXes).

A practical implementation can be found inside the InstallShield Package For The Web (in versions 2.xx, at least) where the packed files are crypted (and decrypted) using a worm generated by Xoring the password and another value, then XORing the result with an hardcoded byte sequence; the second operation in order to destroy the generated periodicity

October 29th, 2001, 12:48
Thnx but I didnt able to say what I wanted to know.Now I make it more clear

In some essays it says proggie xors a table for example to get the valid serial.What does this means?

October 29th, 2001, 13:00
Hello EtErNaL_L0ser !

An example:

A program uses your user name as a password for a xor encryption algorithm. Then it encrypts some data (perhaps 8 times 00h or it's name) with the given password. The encrypted data is your serial number then.

If this sounds familiar to someone, ... (Armadillo )

October 29th, 2001, 14:33
Now I got the idea thnx!

November 10th, 2001, 10:13
Originally posted by ArthaXerXes

Quantum cryptography relies on one-time-pad ciphering, and it works ! The advantage of this system is that you cannot intercept the message without modifying it, hence if Oscar intercepts the transmition between Bob and Alice, it will be discovered at once.

If it interestes i'd like to give a deeper info about this fantastic topic:

This is coz of the Heisenberg indeterministic princip
He tells there r couple of mesures (ie speed and position) 4 which
which u cant get a deeper precision of a certain value (depending on the precision of the other one) in misurating one of them

If u try to guess the exact position of an atom u'll perturbate its speed and vice-versa

Thats coz at quantistic dimension the act of observion implies the perturbation of what u'r observing coz u've to get a signal and signal implies to spend energy and energy transimts from the observer and observed modifying both their states

If oscar intercepts the msg he perturbates the states of the atoms, quantum of energy,... and he get the msg corrupted
and so alice knows thats msg has been intercepted

See ya

November 10th, 2001, 20:41
Quantom encryption can hardly be said to WORK.
Yeah, in theory it's unbreakable, but in reality,
it's of no use.
It can't be implemented (not yet at least, quantum mechanics hasn't evolved enough).
Besides, I'm not sure there is a sure way the
real recipient can ever read the message without
the risk of corruption as well..

I forgot the paper I read about it, but it has
many problems (so does quantum theory actually..)