RC4 / RC4A (Was: One time pad)
in [Cryptography]
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From: me on 24 Jul 2008 07:00 Unruh <unruh-spam(a)physics.ubc.ca> writes: >rossum <rossum48(a)coldmail.com> writes: >>RC4 is very easy to program as a learning >exercise, but is broken. > >Isn't "broken" a bit harsh. Is it anything but a slight bias in the long >term statistics of the output? Ie, if I give you a 1MB file encrypted by >RC4, and give you the first 1K of plaintext, can you recover the rest of >the plaintext? If the algorithm used is RC4-drop(768) RC4-drop(3072), or RC4-drop(65536) (See http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#RC4-drop ) You will need at least a 2GB ciphertext (multiple 1GB ciphertexts are not sufficient) before you can distinguish the ciphertext from random. References: http://www.rsa.com/rsalabs/node.asp?id=2009 http://www.ciphergoth.org/crypto/rc4/ http://en.wikipedia.org/wiki/RC4 http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#RC4-drop http://www.wisdom.weizmann.ac.il/~itsik/RC4/rc4.html http://www.mindspring.com/~dmcgrew/rc4-03.pdf http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Mantin1.zip http://www.drizzle.com/~aboba/IEEE/rc4_ksaproc.pdf http://www.springerlink.com/index/tyqqary0p5kfw7tp.pdf http://www.adastral.ucl.ac.uk/~helger/crypto/link/stream/rc4.php http://www.esat.kuleuven.ac.be/~psourady/research/mypapers/paulv2a.pdf http://www.cosic.esat.kuleuven.be/publications/article-40.pdf Note: The RC4A cipher modifies the RC4 cipher to circumvent its weaknesses. Firstly, RC4A adds a timestamp to the key to prevent the same key from being used twice. Secondly, RC4a drops the first 256 bytes of the RC4 pseudo-random number generator. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "I am convinced that we can do to guns what we've done to drugs: create a multi-billion dollar underground market over which we have absolutely no control." ~George L. Roman "Germans who wish to use firearms should join the SS or the SA - ordinary citizens don't need guns, as their having guns doesn't serve the State." ~Heinrich Himmler, head of Gestapo & Waffen-SS from 1943 to 1945 "Armed people are free. No state can control those who have the machinery and the will to resist, no mob can take their liberty and property. And no 220-pound thug can threaten the well-being or dignity of a 110-pound woman who has two pounds of iron to even things out. People who object to weapons aren't abolishing violence, they're begging for rule by brute force, when the biggest, strongest animals among men were always automatically "right." Guns ended that, and a social democracy is a hollow farce without an armed populace to make it work. ~L. Neil Smith An armed person is a citizen. An unarmed person is a subject. Gun control is not about guns; it's about control. Free men do not ask permission to bear arms. What part of "shall not be infringed" don't you understand? The Second Amendment is in place in case they ignore the others. A gun in the hand is better than a cop on the phone. Criminals love gun control - it makes their jobs safer. When you remove the people's right to bear arms, you create slaves. |