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If I have the unencrypted version of a file, and encrypted version of the same file, is it possibly to determine the encryption scheme used to encrypt the file, and possibly even the encryption key?
".45 ACP - because shooting twice is just silly" - JSOP, 2010
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You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
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When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013
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If both files are the same length you can just go and assume a one time pad where
encryptedText = clearText XOR OneTimePad
so you can create the one time pad from encryptedText XOR clearText. That doesn't mean it really was a one time pad that was being used for encryption, but if both encrypted and clear text have the same length one can just create a one time pad from both.
Anyhow having clear text as well as the encrypted version allows for some crypt analysis.
Cheers!
"I had the right to remain silent, but I didn't have the ability!"
Ron White, Comedian
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Not if multiple passes were made.
This space intentionally left blank.
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It depends on the encryption method: the simple methods such as substitution cyphers are wide open to it (for Caesar cypher, you only need one character from the original!) and early PKZIP encryption was also susceptible.
Modern AES / DES based encryption methods are not open to such attacks,.
Those who fail to learn history are doomed to repeat it. --- George Santayana (December 16, 1863 – September 26, 1952)
Those who fail to clear history are doomed to explain it. --- OriginalGriff (February 24, 1959 – ∞)
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If the length of both files is the same there's a reasonable chance the file could have been encrypted using RC4 or Alleged RC4 as that guarantees the encrypted length will be the same as the unencrypted. I can't help with the key issue unfortunately.
If there is one thing more dangerous than getting between a bear and her cubs it's getting between my wife and her chocolate.
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During WW2 the boffins at Bletchley Park would arrange particular missions, such as laying mines in enemy harbours, because the knew that this would be reported back to Army/Navy headquarters using standard message templates. Knowing what you are looking for helps to reduce the work needed to decrypt.
They also intercepted enemy weather forecasts, which were encoded using a weather code book, then encrypted using Enigma machines. Using captured codebooks, this helped them crack the Navy 4-rotor Enigma, as the same forecast was transmitted to lower security establishments such as shipyards using a standard 3 rotor systeme, while the U-boats got it in 4 rotor format. The 3-rotor encryption could be broken on a daily basis, and knowing what thety were looking for in a 4 rotor message certainly helped in the breaking of that.
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I'm an optoholic - my glass is always half full of vodka.
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he will ban Facebook and Youtube in Turkey after the next election. I'm sorry guys, I can't help you about Facebook API anymore !!  What a country !! Our fake sultan lost his mind.
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What is he trying to protect you from? 
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Mike Hankey wrote: What is he trying to protect you from?
Liberty, freedom and self determination.
The difficult we do right away...
...the impossible takes slightly longer.
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Richard Andrew x64 wrote: Liberty, freedom and self determination.
Ah, I thought they were trying to keep them from finding out about Bacon. 
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Mike Hankey wrote: Ah, I thought they were trying to keep them from finding out about Bacon.
He is trying to protect the people from infidels like you. 
The report of my death was an exaggeration - Mark Twain
Simply Elegant Designs JimmyRopes Designs
I'm on-line therefore I am.
JimmyRopes
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Mike Hankey wrote: Ah, I thought they were trying to keep them from finding out about Bacon.
I don't like bacon. What bothers me is his policies about wine and raki.
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Vedat Ozan Oner wrote: I don't like bacon.
I wouldn't utter that to loudly around here with all all the carnivores.
Vedat Ozan Oner wrote: What bothers me is his policies about wine and raki.
I don't know what his policies on these subjects are but the rest of the world expects y'all to keep up with production and consumption.
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Mike Hankey wrote: What is he trying to protect you from?
Maybe from politics in the lounge. *whistles innocently*
"I had the right to remain silent, but I didn't have the ability!"
Ron White, Comedian
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No surely not, we're not corrupting them are we?
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Mike Hankey wrote: we're not corrupting them are we?
Said while offering his guest a bacon wrapped turkey[^] sandwich.
The report of my death was an exaggeration - Mark Twain
Simply Elegant Designs JimmyRopes Designs
I'm on-line therefore I am.
JimmyRopes
modified 7-Mar-14 23:49pm.
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Mike Hankey wrote: What is he trying to protect you from yourself?
FTFY
The report of my death was an exaggeration - Mark Twain
Simply Elegant Designs JimmyRopes Designs
I'm on-line therefore I am.
JimmyRopes
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Too many cat videos on youtube?
That's too bad. Hopefully you will still find a way to get around it without getting in trouble. Can't get enough cat videos. 
It was broke, so I fixed it.
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S Houghtelin wrote: Too many cat videos on youtube?
Have you heard the cat joke about this lady gets ... err ... never mind. 
The report of my death was an exaggeration - Mark Twain
Simply Elegant Designs JimmyRopes Designs
I'm on-line therefore I am.
JimmyRopes
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Banning facebook would probably increase workplace productivity significantly.
Banning YouTube would probably increase literacy across the board.
Not bad ideas, really
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Turks had more freedom when the army had more power, and protected Mustafa Kemal's legacy. I lived in Ankara (worked at Genel Kurmay Başkanlığı) in the mid-1970s, when the generals were often in the news, but it was still a lively and interesting place to be.
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What I think is that Mustafa Kemal's legacy has to be protected by people, not by army or some other institution. when you delegate your duty to other party, you risk it somehow. Ataturk knew that and said those great words to Turkish youth.
http://www.ataturkungencligehitabesi.com/[^] This is in Turkish but google-translate translates well enough to get the main idea.
Unfortunately, we ended up this fake sultan.
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If it's any consolation most countries these days seem to have the wrong leaders.
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uneducated people, wrong leader.
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