Comments on: RC4Encryption : Encrypt and decrypt files with RC4 http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/ Thu, 01 Dec 2011 18:03:30 +0000 hourly 1 http://wordpress.org/?v=3.3 By: DNT http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-1606 DNT Sun, 18 Apr 2010 14:47:25 +0000 http://www.megapanzer.com/?p=2111#comment-1606 can someone show the example of source code of user and Kernel level API unhooking function? can someone show the example of source code of user and Kernel level API unhooking function?

]]> By: TC http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-670 TC Wed, 23 Sep 2009 07:26:52 +0000 http://www.megapanzer.com/?p=2111#comment-670 @Zeri: I'm not sure what you're trying to say now. You originally said (and I quote): "you[r] code seems broken … [if] I know the plaintext of A and the ciphertexts of A and B … then I think its possible the recover the plaintext of B" That comment clearly showed, that you did not understand stream ciphers. What you said, is true of MANY, if not ALL, stream ciphers. His code is not "broken" in any way, shape or form. @Zeri: I’m not sure what you’re trying to say now.

You originally said (and I quote):

“you[r] code seems broken … [if] I know the plaintext of A and the ciphertexts of A and B … then I think its possible the recover the plaintext of B”

That comment clearly showed, that you did not understand stream ciphers. What you said, is true of MANY, if not ALL, stream ciphers. His code is not “broken” in any way, shape or form.

]]> By: zeri http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-582 zeri Tue, 08 Sep 2009 16:26:13 +0000 http://www.megapanzer.com/?p=2111#comment-582 of course I dint mean to recover the key but a "defacto key" (keystream) -Zeri of course I dint mean to recover the key but a “defacto key” (keystream)

-Zeri

]]> By: zeri http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-581 zeri Tue, 08 Sep 2009 16:24:57 +0000 http://www.megapanzer.com/?p=2111#comment-581 @tc: the problem is, that normaly you deploy initialisationvectors in order to prevent that kind of attak. In case of rc4 you could simply concat some random bytes with the key and place these n-bytes in front of the ciphertext .... as long as you dont use the same iv twice with the same key there is no way to recover the key from simply knowing the plaintext of one of the files. -Zeri PS: thank you for the information, but I was allready aware of the meaning of known plaintext attacks ^^ thats why I wrote a comment in the first time. @tc: the problem is, that normaly you deploy initialisationvectors in order to prevent that kind of attak. In case of rc4 you could simply concat some random bytes with the key and place these n-bytes in front of the ciphertext …. as long as you dont use the same iv twice with the same key there is no way to recover the key from simply knowing the plaintext of one of the files.

-Zeri
PS: thank you for the information, but I was allready aware of the meaning of known plaintext attacks ^^ thats why I wrote a comment in the first time.

]]> By: TC http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-578 TC Sat, 05 Sep 2009 13:10:04 +0000 http://www.megapanzer.com/?p=2111#comment-578 @zeri: This is a well known attack on symmetric stream ciphers like RC4. Look up "stream cipher", and "known plaintext attack. PS. It's a bit disingenuos to say that people can "use this code without any dependency of an additional library". RC4 is extremely simple (it is literally only a few lines of code), and is available in "stand alone" form in every conceivable language, all over the web! @zeri: This is a well known attack on symmetric stream ciphers like RC4. Look up “stream cipher”, and “known plaintext attack.

PS. It’s a bit disingenuos to say that people can “use this code without any dependency of an additional library”. RC4 is extremely simple (it is literally only a few lines of code), and is available in “stand alone” form in every conceivable language, all over the web!

]]> By: zeri http://www.megapanzer.com/2009/06/09/rc4encryption-encrypt-and-decrypt-files-with-rc4/comment-page-1/#comment-486 zeri Wed, 26 Aug 2009 22:42:26 +0000 http://www.megapanzer.com/?p=2111#comment-486 you code seems broken ... This may sound a bit arrogant (sorry for it in advance). But what happens if you take 2 Files A,B with lenght(A) > length(B) and I know the plaintext of A and the ciphertexts of A and B ... then I think its possible the recover the plaintext of B as follows: plainB[i] = B[i] xor A[i] xor plainA[i] maybe I am completly misstaken ... I will implement it tomorrow (dont have a windows box at hand). -Zeri you code seems broken …

This may sound a bit arrogant (sorry for it in advance). But what happens if you take 2 Files A,B with lenght(A) > length(B) and I know the plaintext of A and the ciphertexts of A and B … then I think its possible the recover the plaintext of B as follows:

plainB[i] = B[i] xor A[i] xor plainA[i]

maybe I am completly misstaken … I will implement it tomorrow (dont have a windows box at hand).

-Zeri

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