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Stream ciphers are an alternative to block ciphers.

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RC 4 is a good example of a stream cipher this code has also been developed by Ron reversed.

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If you configure the previous three modes in such a way that shifts are single bit the result would

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be a stream cypher block sizes one bit.

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The blocks are encrypted bit by bit using a long key.

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There are some ciphers that employ a mode of operation that is exactly like that.

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They are frequently used for transmissions.

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One of the most popular applications of for it was the point of point Tamplin protocol the method used

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in Microsoft implementations of virtual private networks.

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RC 4 was developed in 1987 and its operating principle was disclosed in 1994.

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RC for exhibits a striking similarity to the perfect one time pad cipher.

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The difference is that you have to lengthen that key artificially.

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It's it's

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even though the algorithm itself has been tested and regarded as secure.

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Implementing it can cause problems all earlier versions of Microsoft Office are a good example of RC

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for implementation problems

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in other instances the operating system SAM file.

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We talked about this before.

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You've probably noticed that if you're using Office 97 or Office 2003 you have the ability to encrypt

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Word Excel and Powerpoint files

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the RC for Cypher was the default cipher used for this.

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There is a huge amount of tools for retrieving forgotten office passwords on the Internet.

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They are very affordable.

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Why is that.

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The basic problem Marsi foreheads is that you shouldn't reuse the key to encrypt the same message the

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Ekso our operation is performed there.

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But if the key is re-used an attacker can reverse the ex-SO or and disclose some information on the

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plaintext and the keys as well.

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It's easy to see that if you encrypt the same data multiple times using R-S.C. for if the kids the same

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the ciphertext will be the same each time Microsoft implementations use the same key every time

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and now will briefly tell you about the operation

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at first a keystream has to be generated then the keystream needs to be combined with the original plaintext

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using the x or operation.

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After this process is completed the result is very much like the one time Pead except the keystream

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here has lesser entropy than that perfect cipher

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to generate the cipher you need a secret and initial state the initial state is usually generated by

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a permutation of the 256 state box and 2 8 bit index pointers once the vectors A keystream initial state

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is generated it can be made longer to match the length of the plaintext.