# Thread: why not use random?

1. ## why not use random?

hi!
In classical cryptograph, there are two methods: metathesis and substitute. But their are not safe enough. if use two techniques at the same time and lead in the random number, then the encipher will be strong enough.
Example. X is the message data, Y is the cryptograph, D is the random list. Z is the metathesis matrix, K is user key.
steps: 1, get a message data list X.
2, get a random list D, D is big as X.
3, create Z base on D.
4, encrypt x with Z,D,K: Y1=(Z*X) XOR (Z*Z*D) XOR (Z*Z*Z*K)
5, encrypt D with K: Y2=D XOR K
6, cryptograph include Y1,Y2.

In this way, it need not several time encrypt. And because the D, we can get other function: faster, easy to test...
Now, why peoper use AES or DSE that need several time encrypt? the D is not safe enough?
I think that confusion and pervasion may be work, but the random number will be better, it is easyer and faster.

2. Not sure but IIRC computers don't produce 'true' random numbers but pseudo-random numbers.

3. Boiled down, the message is behind two locked doors, the first door is decrypting D and once you've done that, you've got enough information to open the next door straight away.
The weak point (apart from the human one) is part 5, "encrypt D with K" how? If D can be easily found, I can't see that it'd be at all difficult to handle the rest.

SirDice, yes but some pseudo-random number generators are really bloody good, the effort of cracking a good one isn't always worth it.

4. if the user key K is safe keeped, the D is safe.
May be the RC4 can create safe random number

5. Originally Posted by xuzijie
if the user key K is safe keeped, the D is safe.
Assuming that a good algorithm is used to encrypt D against K, which you haven't specified.

6. Originally Posted by the tree
Assuming that a good algorithm is used to encrypt D against K, which you haven't specified.
Th point is use random number. encrypt D at step 5: Y2=D XOR K.
my english is not good, i can express clear in chinese. the example just is a example, in fact ,it is not fast enough.

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