$ \begingroup $ To add to what fgrieu said, intend of RC4 as a self-modifying rotor. Imagine a wheel with little tiles on it like Scrabble tiles, but labeled 0x00 to 0xff ( or 0 to 255 ). Each time you crank out a value, you flip some tiles on the rotor and ratchet it one place .
You initialize the wheel by spinning it wholly once, using your key as values to control how tiles get flipped around. 2048 bits is rotating the wheel a accomplished revolution and using your own control bits on every chatter of the wheel .
You could obviously do it with any size control condition string ( winder ), but it obviously has much less value to do it more than one complete rotation. sol precisely as by convention there ‘s a minimum of 8 bytes ( 40 bits ) of key, there ‘s a soap of 256 bytes.

We call RC4 ‘s low-level formatting a “ key schedule ” but it is n’t a key schedule the way that a cardinal schedule is done for a stuff zero. typically a forget code has a number of sub-keys that are mix in as the cipher runs and the sub-keys are derived from the establish key, and that ‘s what we call a cardinal agenda. RC4 has an low-level formatting — the rotor is initialized and then you barely run it like a pseudo-random count generator and XOR those onto the plaintext .
RC4 has a helplessness that the low-level formatting is faint. The distinctive hypnotism to strengthen it is to generate N ( normally 256 or 512 ) bytes of the stream and throw them away. That ‘s turning the rotor once or twice, just to mix it up more.

WEP used RC4 in a spectacularly bogus way, but that ‘s a wholly different discussion, because one of the things WEP should not have done was to use a current cipher at all. Stream ciphers follow the model of creating a PRNG and then XORing against plaintext. If you use the same flow on every packet ( which WEP did ), then if you have known plaintext, you can derive the key pour byte, and then decrypt that byte on every packet that always follows. You then good make guesses about the lie of the plaintext to get the whole of the flow .
You should never, ever, ever use the same key twice on any stream code. not RC4, not a block cipher with counter modality, nothing. This approach model ( use known plaintext to guess key stream bytes, and then guess more plaintext ) works for any pour calculate with any size key.

While I ‘m at it, RC4 has lots of fiddling holes. It ‘s not therefore bad that you should rip it out of a place where it is being used ( and there are places where the alternatives have their own problems ), but in a fresh visualize, you should do something like anticipate mode that has better properties .
however, RC4 is in my impression, possibly the most beautiful cipher ever made, and I have a affection for it. I understand liking it because it ‘s so reasonably .

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