krytpografia ALGORYTM

Witam, jaki polecacie szybki algoryt a zarazem "w miare" bezpieczny.

Teraz stosuje Xor + salt gdyz te operacje sa bardzo szybkie, ale chce jak
posiadam:
dane o dlugosci 10 znakow
oraz klucz o dlugosci tez 10 znakow to salt mi nie pomoze poniewaz dodaje
sie go na koncu klucza (chyba ze cos zle robie)

Porsze o pomoc

A nie przypadkiem XLAT? Xlat sie nie nadaje do szyfrowania
bo mozna tylko wymyslic przy pomocy tej instrukcji
szyfr, ktory jednej wartosci przyporzadkuje inna.

Jezeli dlugosc klucza jest rowna lub wieksza
od danych do zakodowania tym kluczem (np. xor)
to dane sa nie do odszyfrowania.

Mylisz się. Przy małej ilości znaków i XOR - tekst jawny jest zdeterminowany
do długości tekstu zaszyfrowanego. Znając cel działania, i/lub
przypuszczając jakie słowa mogły być tekstem jawnym ograniczamy znacznie
ilość kroków deszyfracji. W tym przypadku atak słownikowy ma znaczne szanse
powodzenia. Pamiętaj, że znaczenie ma też ilość próbek jakimi dysponujemy.
Jeśli mamy ich co więcej niż jedną - to po robocie. Myślę, że w godzinę się
można z tym uporać. :)))
pozdro
Bogdan

Wojciech Tomaszewski wyrzeźbił(a):

nie cytuj całych postów odpowiadając na kawałek.

co do mylenia - nie sądzę. zakładając że za każdym razem szyfruję innym
kluczem o dłgości równej lub większej od długości tekstu jawnego - nie
da się tego zdekodować. a szyfrowanie xorem z wielokrotnym użyciem
klucza jest na tyle głupie, że nie sądzę by ktokolwiek używał
czegokolwiek takiego.

depesz

Zdarza się, zdarza. I to nie tylko XOR, ale także w przypadku innych
algorytmów o podobnych słabościach.

Aczkolwiek nie nalezy popelnic takiego bledu, by klucz i tekst
byly skorelowane. Np. uzywanym zestawem znakow.

Salt jest losowym modyfikatorem klucza lub tekstu jawnego wprowadzanym by
ten sam tekst jawny szyfrowany wielokrotnie tym samym kluczem dawał zawsze
inne kryptogramy
Chronił się w ten sposób przed atakiem słownikowym.

1. Czytaj i wyciągaj właściwe wnioski:

Wnioski jakie ja wyciągnąłem:
a) jeśli stosuje salt, to szyfruje jednym kluczem
b) szuka szybkiego algorytmu, więc ma dużo danych do zaszyfrowania
c) jeśli szuka algorytmu, to sam szyfruje dane (sam pisze program)
Wniosek daleko idący:
a) chce zaszyfrować listę haseł zdeterminowanych do długości 10 znaków, a
sam ma swoje 1 hasło uniwersalne, które ma być kluczem.
(wniosek wywodzę z podstawowego zastosowania SALT: w uniksowej funkcji crypt
używanej do szyfrowania haseł)

Odpowiadając Hubertowi depeszowi:

Otóż da się.
Polega to na tym, że znajomość XOR-a pozwala wykorzystać metody statystyczne
by odsłonić prosty tekst.
Przy tak krótkim kluczu można spokojnie, w krótkim czasie zdekodować
zaszyfrowaną wiadomość.
Nawet w przypadku stosowania SALT i nawet w przypadku zastosowania różnych
kluczy
(co tutaj akurat nie ma miejsca)

Rada dla Hubert depesz:
Patrząc na Twój post widzę ogromną determinację dążenia do nieomylności oraz
stanowczość i trochę arogancji.
Slow down :)

pozdro dla wszystkich
BWT

Wojciech Tomaszewski wyrzeźbił(a):

moment. wydaje mi się, że mylisz np. algorytmy typu crypt z tym o czym
pisał oryginalny piszący.

ma tekst jawny:
"aaaaaaaaa"
generuje ciąg hasła/klucza:
"bbbbbbbbb"
dostaje jakiś tam wynik (w tym przypadku 9 znaków chr(3)) i dokleja do
tego klucz (bbbbbbbbb).

a dla ciebie zagadka. skoro xora tak łatwo zekodować, to zdekoduj to:
1A 57 08 D3 04 4D 55 D6 C6 57 12 5A 0A 0F 98 4F 1D 04 0A 07 0A 52 19 15 1D 12 14 43 02 45 18 18 55 01 1F 03 5D 0D 00 13 1F 1D 1F
to jest ultra prosty "szyfr" xorowy. jeden xor. wiadomość jawna i klucz

depesz

with you
against the segregated school system because it's criminal, because it
is absolutely destructive, in every way imaginable, to the minds of the
children who have to be exposed to that type of crippling education.

Last but not least, I must say this concerning the great controversy
over rifles and shotguns. The only thing that I've ever said is that in
areas where the government has proven itself either unwilling or unable
to defend the lives and the property of Negroes, it's time for Negroes
to defend themselves. Article number two of the constitutional
amendments provides you and me the right to own a rifle or a shotgun. It
is constitutionally legal to own a shotgun or a rifle. This doesn't mean
you're going to get a rifle and form battalions and go out looking for
white folks, although you'd be within your rights -- I mean, you'd be
justified; but that would be illegal and we don't do anything illegal.
If the white man doesn't want the black man buying rifles and shotguns,
then let the government do its job.

That's all. And don't let the white man come to you and ask you what you
think about what Malcolm says -- why, you old Uncle Tom. He would never
ask you if he thought you were going to say, "Amen

by the
people who came here on the "Mayflower." You were brought here by the
so-called Pilgrims, or Founding Fathers. They were the ones who brought
you here.

We have a common enemy. We have this in common: We have a common
oppressor, a common exploiter, and a common discriminator. But once we
all realize that we have this common enemy, then we unite on the basis
of what we have in common. And what we have foremost in common is that
enemy -- the white man. He's an enemy to all of us. I know some of you
all think that some of them aren't enemies. Time will tell.

In Bandung back in, I think, 1954, was the first unity meeting in
centuries of black people. And once you study what happened at the
Bandung conference, and the results of the Bandung conference, it
actually serves as a model for the same procedure you and I can use to
get our problems solved. At Bandung all the nations came together. Their
were dark nations from Africa and Asia. Some of them were Buddhists.
Some of them were Muslim. Some of them were Christians. Some of them
were Confucianist

from Angola and
was being colonized by the Portuguese. When they came to the Bandung
conference, they looked at the Portuguese, and at the Frenchman, and at
the Englishman, and at the other -- Dutchman -- and learned or realized
that the one thing that all of them had in common: they were all from
Europe, they were all Europeans, blond, blue-eyed and white-skinned.
They began to recognize who their enemy was. The same man that was
colonizing our people in Kenya was colonizing our people in the Congo.
The same one in the Congo was colonizing our people in South Africa, and
in Southern Rhodesia, and in Burma, and in India, and in Afghanistan,
and in Pakistan. They realized all over the world where the dark man was
being oppressed, he was being oppressed by the white man; where the dark
man was being exploited, he was being exploited by the white man. So
they got together under this basis -- that they had a common enemy.

And when you and I here in Detroit and in Michigan and in America who
have been awakened today look around us, we too realize here in America
we all have a common enemy, whether he's in Georgia or Michigan, whether
he's in California or New York. He's

Richard Russell.
When Johnson became president, the first man he asked for when he got
back to Washington, D.C., was "Dicky" -- that's how tight they are.
That's his boy, that's his pal, that's his buddy. But they're playing
that old con game. One of them makes believe he's for you, and he's got
it fixed where the other one is so tight against you, he never has to
keep his promise.

So it's time in 2005 to wake up. And when you see them coming up with
that kind of conspiracy, let them know your eyes are open. And let them
know you -- something else that's wide open too. It's got to be the
ballot or the bullet. The ballot or the bullet. If you're afraid to use
an expression like that, you should get on out of the country; you
should get back in the cotton patch; you should get back in the alley.
They get all the Negro vote, and after they get it, the Negro gets
nothing in return. All they did when they got to Washington was give a
few big Negroes big jobs. Those big Negroes didn't need big jobs, they
already had jobs. That's camouflage, that's trickery, that's treachery,
window-dressing. I'm not trying to knock out the Democrats for the
Republicans. We'll get to them in a minute. But it is true; you put the
Democrats first and the Democrats put you last.

Look at it the way it is. What alibis do they use, since they control
Congress and the Senate? What alibi do they use when you and I ask,
"Well, when are you going to keep your promise?" They blame the
Dixiecrats. What is a Dixiecrat? A Democrat. A Dixiecrat is nothing but
a Democrat in disguise. The titular head of the Democrats is also the
head of the Dixiecrats, because the Dixiecrats are a part of the
Democratic Party. The Democrats have never kicked the Dixiecrats out of
the party. The Dixiecrats bolted the

any singing; you're too busy swinging. It's based on land. A
revolutionary wants land so he can set up his own nation, an independent
nation. These Negroes aren't asking for no nation. They're trying to
crawl back on the plantation.

When you want a nation, that's called nationalism. When the white man
became involved in a revolution in this country against England, what
was it for? He wanted this land so he could set up another white nation.
That's white nationalism. The American Revolution was white nationalism.
The French Revolution was white nationalism. The Russian Revolution too
-- yes, it was -- white nationalism. You don't think so? Why [do] you
think Khrushchev and Mao can't get their heads together? White
nationalism. All the revolutions that's going on in Asia and Africa
today are based on what? Black nationalism. A revolutionary is a black
nationalist. He wants a nation. I was reading some beautiful words by
Reverend Cleage, pointing out why he couldn't get together with someone
else here in the city because all of them were afraid of being
identified with black nationalism. If you're afraid of black
nationalism, you're afraid of revolution. And if you love revolution,
you love black nationalism.

To understand this, you have to go back to what [the] young brother here
referred to as the house Negro and the field Negro -- back during
slavery. There was two kinds of slaves. There was the house Negro and
the field Negro. The house Negroes - they lived in the house with
master, they dressed pretty good, they ate good 'cause they ate his food
-- what he left. They lived i

da sie ale kazdy otrzymany "plaintext" jest wtedy jednakowo prawdopodobny :

Piotr Kulinski
www.ipsec.pl