- Stream Cipher Key Stream Generator Reviews
- Stream Cipher Ppt
- Stream Cipher Key Stream Generator Online
Stream Cipher Design Considerations. A pseudorandom number generator uses a function that produces a deterministic stream of bits that eventually repeats; the longer the period of repeat the more difficult it will be to do cryptanalysis The encryption sequence should have a large period The encryption sequence should have a large period. There should be an approximately equal number of 1s and 0s. If the keystream is treated as a stream of bytes, then all of the 256 possible byte. Hi i am trying to build a key stream generator for my homemade stream cipher.The key stream output has a close to maximum entropy value and a large periodicity. What does it take for this generator to be secure from various attacks? What does a high entropy mean security wise? I am confused with this at the moment. Thank you for spending your time. The LILI-128 keystream generator is a LFSR based synchronous stream cipher with a 128 bit key. The design o#ers large period and linear complexity, and is resistant to currently known styles of. A stream cipher is an encryption algorithm that encrypts 1 bit or byte of plaintext at a time. It uses an infinite stream of pseudorandom bits as the key. For a stream cipher implementation to remain secure, its pseudorandom generator should be unpredictable and the key should never be reused. A Stream Cipher is used for symmetric key cryptography, or when the same key is used to encrypt and decrypt data. Stream Ciphers encrypt pseudorandom sequences with bits of plaintext in order to generate ciphertext, usually with XOR. A good way to think about Stream Ciphers is to think of them as generating one-time pads from a given state.
![Popular stream ciphers Popular stream ciphers](/uploads/1/2/6/6/126623391/539905281.png)
In cryptography, a keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted message (the ciphertext).
The 'characters' in the keystream can be bits, bytes, numbers or actual characters like A-Z depending on the usage case.
Usually each character in the keystream is either added, subtracted or XORed with a character in the plaintext to produce the ciphertext, using modular arithmetic.
Keystreams are used in the one-time pad cipher and in most stream ciphers. Block ciphers can also be used to produce keystreams. For instance, CTR mode is a block mode that makes a block cipher produce a keystream and thus turns the block cipher into a stream cipher.
![Generator Generator](/uploads/1/2/6/6/126623391/532896688.png)
Example[edit]
Stream Cipher Key Stream Generator Reviews
In this simple example we use the English alphabet of 26 characters from a-z. Thus we can not encrypt numbers, commas, spaces and other symbols. The random numbers in the keystream then have to be at least between 0 and 25.
To encrypt we add the keystream numbers to the plaintext. And to decrypt we subtract the same keystream numbers from the ciphertext to get the plaintext.
If a ciphertext number becomes larger than 25 we wrap it to a value between 0-25. Thus 26 becomes 0 and 27 becomes 1 and so on. (Such wrapping is called modular arithmetic.)
Here the plaintext message 'attack at dawn' is combined by addition with the keystream 'kjcngmlhylyu' and produces the ciphertext 'kcvniwlabluh'.
Plaintext | a | t | t | a | c | k | a | t | d | a | w | n |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Plaintext as numbers | 0 | 19 | 19 | 0 | 2 | 10 | 0 | 19 | 3 | 0 | 22 | 13 |
Keystream | k | j | c | n | g | m | l | h | y | l | y | u |
Keystream as numbers | 10 | 9 | 2 | 13 | 6 | 12 | 11 | 7 | 24 | 11 | 24 | 20 |
Ciphertext as numbers | 10 | 28 | 21 | 13 | 8 | 22 | 11 | 26 | 27 | 11 | 46 | 33 |
Ciphertext as numbers wrapped to 0-25 | 10 | 2 | 21 | 13 | 8 | 22 | 11 | 0 | 1 | 11 | 20 | 7 |
Ciphertext as text | k | c | v | n | i | w | l | a | b | l | u | h |
Stream Cipher Ppt
References[edit]
- Handbook of Applied Cryptography by Menezes, van Oorschot and Vanstone (2001), chapter 1, 6 and 7.
Stream Cipher Key Stream Generator Online
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