9/27/2020 Key Generation In Stream Cipher
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).
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The RC4 Encryption Algorithm, developed by Ronald Rivest of RSA, is a shared key stream cipher algorithm requiring a secure exchange of a shared key. RC4 is no longer considered secure and careful consideration should be taken regarding it’s use. 11 hours ago The best encryption software to protect your data and your business. Users can choose to leverage their iCloud account credentials or generate a recovery key. For ciphers other than block ciphers, for example RSA or ECDHE (on curves other than ed25519), keys are not just random bytes and in fact have a lot of mathematical structure inside them. These algorithms have complicated key generation routines, so you'll need to go find the specification for the algorithm you're trying to implement. Principles of Pseudorandom Number Generation 2. Pseudorandom number generators 3. Pseudorandom number generation using a block cipher 4. Stream Cipher 5. RC4 These slides are based on Lawrie Brown’s slides supplied with William Stalling’s book “Cryptography and Network Security: Principles and Practice,” 7 th Ed, 2017.
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.
Example[edit]
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'.
References[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Keystream&oldid=848603541'
The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).
DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). General Structure of DES is depicted in the following illustration −
Key Generator Stream Cipher![]()
Since DES is based on the Feistel Cipher, all that is required to specify DES is −
Initial and Final Permutation
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. The initial and final permutations are shown as follows −
Round Function
The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.
Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration −
The logic for Parity drop, shifting, and Compression P-box is given in the DES description.
DES Analysis
The DES satisfies both the desired properties of block cipher. These two properties make cipher very strong.
Key Generation In Stream Cipher Windows 10
During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. These keys shall be avoided.
Code Cipher Keys
DES has proved to be a very well designed block cipher. There have been no significant cryptanalytic attacks on DES other than exhaustive key search.
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