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Diffusion means that if we change a single bit of the plaintext, then about half of the bits in the ciphertext should change, and similarly, if we change one bit of the ciphertext, then about half of the plaintext bits should change. [5] This is equivalent to the expectation that encryption schemes exhibit an avalanche effect.
In the case of high-quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext. The actual term was first used by Horst Feistel, [1] although the concept dates back to at least Shannon's diffusion. The SHA-1 hash function exhibits good avalanche effect. When a single bit is ...
A code maps one meaning with another. Words and phrases can be coded as letters or numbers. Codes typically have direct meaning from input to key. Codes primarily function to save time. Ciphers are algorithmic. The given input must follow the cipher's process to be solved. Ciphers are commonly used to encrypt written information.
For example, encryption using an oversimplified three-round cipher can be written as = ((())), where C is the ciphertext and P is the plaintext. Typically, rounds R 1 , R 2 , . . . {\displaystyle R_{1},R_{2},...} are implemented using the same function, parameterized by the round constant and, for block ciphers , the round key from the key ...
Rather, in a good S-box each output bit will be affected by every input bit. More precisely, in a good S-box each output bit will be changed with 50% probability by every input bit. Since each output bit changes with the 50% probability, about half of the output bits will actually change with an input bit change (cf. Strict avalanche criterion ...
The propagating cipher block chaining [25] or plaintext cipher-block chaining [26] mode was designed to cause small changes in the ciphertext to propagate indefinitely when decrypting, as well as when encrypting. In PCBC mode, each block of plaintext is XORed with both the previous plaintext block and the previous ciphertext block before being ...
Salsa20, the original cipher, was designed in 2005, then later submitted to the eSTREAM European Union cryptographic validation process by Bernstein. ChaCha is a modification of Salsa20 published in 2008. It uses a new round function that increases diffusion and increases performance on some architectures. [4]
F is a nonlinear function; one function is used in each round. M i denotes a 32-bit block of the message input, and K i denotes a 32-bit constant, different for each operation. <<< s denotes a left bit rotation by s places; s varies for each operation. denotes addition modulo 2 32.