Stream ciphers are an alternative to block ciphers.
RC 4 is a good example of a stream cipher this code has also been developed by Ron reversed.
If you configure the previous three modes in such a way that shifts are single bit the result would
be a stream cypher block sizes one bit.
The blocks are encrypted bit by bit using a long key.
There are some ciphers that employ a mode of operation that is exactly like that.
They are frequently used for transmissions.
One of the most popular applications of for it was the point of point Tamplin protocol the method used
in Microsoft implementations of virtual private networks.
RC 4 was developed in 1987 and its operating principle was disclosed in 1994.
RC for exhibits a striking similarity to the perfect one time pad cipher.
The difference is that you have to lengthen that key artificially.
It's it's
even though the algorithm itself has been tested and regarded as secure.
Implementing it can cause problems all earlier versions of Microsoft Office are a good example of RC
for implementation problems
in other instances the operating system SAM file.
We talked about this before.
You've probably noticed that if you're using Office 97 or Office 2003 you have the ability to encrypt
Word Excel and Powerpoint files
the RC for Cypher was the default cipher used for this.
There is a huge amount of tools for retrieving forgotten office passwords on the Internet.
They are very affordable.
Why is that.
The basic problem Marsi foreheads is that you shouldn't reuse the key to encrypt the same message the
Ekso our operation is performed there.
But if the key is re-used an attacker can reverse the ex-SO or and disclose some information on the
plaintext and the keys as well.
It's easy to see that if you encrypt the same data multiple times using R-S.C. for if the kids the same
the ciphertext will be the same each time Microsoft implementations use the same key every time
and now will briefly tell you about the operation
at first a keystream has to be generated then the keystream needs to be combined with the original plaintext
using the x or operation.
After this process is completed the result is very much like the one time Pead except the keystream
here has lesser entropy than that perfect cipher
to generate the cipher you need a secret and initial state the initial state is usually generated by
a permutation of the 256 state box and 2 8 bit index pointers once the vectors A keystream initial state
is generated it can be made longer to match the length of the plaintext.