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4

You can do something like what you are suggesting. But, the EC_Dual_DBRG also has biases in the stream and so you cannot use it without changes (e.g., truncating much more). However, this is based on the same operations as ElGamal. The public key is set up exactly as proposed. Then, to encrypt a message $m$ of any length, do: Choose a random ...

0

I would be inclined not to even call it a stream cipher. If I had to give it a name, it would be reactive encryption algorithm or perhaps forward reactive encryption algorithm. This name implies what it does, which is react to the plaintext in some way going forward, rather than simply encrypting it. You can build something like this very easily using the ...

3

Logically I think that should also be a synchronous stream cipher. The word refers to the fact that the keystreams must be synchronized between the encrypter and the decrypter to allow decoding. With anything other than a self-synchronizing cipher that is the case. However, that does not mesh with existing usage. You will find many texts (example) saying ...

4

A stream cipher, by definition, acts on individual bits at a time. This effectively means that bits later in the plaintext cannot affect bits around the beginning of the ciphertext. It can, however, feed the ciphertext back into the state of the PRNG to affect all future bits. This can be seen in the CFB (Cipher Feedback) block cipher mode. It acts similarly ...

2

The reason for the padding (and re-positioning of the AAD length) in the later draft is to make implementations easier and faster - i.e. not for a security reason. The rationale for this change was actually documented on the CFRG mailing list by Alyssa Rowan: Instead of the lengths directly following their ciphertexts: ...

2

The reference definition of Spritz seems to be: Ronald L. Rivest and Jacob C. N. Schuldt, Spritz - a spongy RC4-like stream cipher and hash function, presented at Charles River Crypto Day (2014). The code snippet of the question shows how the state of Spritz repeatedly used in DBRG output mode is updated and its next output byte $z$ produced; the state ...

4

To build on mikeazo's answer (since it's not really practical to post code in comments), here's a quick Python program that takes any two permutations of $\{0, \dots, 255\}$ and generates a key that transforms one into the other when run through the RC4 key setup: # source and target permutations s = range(256) t = [181, 172, 179, 178, 177, 168, 175, 174, ...

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