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In cryptography, the shrinking generator is a form of pseudorandom number generator intended to be used in a stream cipher. It was published in Crypto 1993 by Don Coppersmith, Hugo Krawczyk and Yishay Mansour. [1] The shrinking generator uses two linear-feedback shift registers.
The attack relied on the fact that the cipher has identical subkeys in each round, so the cipher had a cyclic key schedule with a cycle of only one key, which makes it an early version of the slide attack. A summary of the report, including a description of the NDS block cipher and the attack, is given in Cipher Systems (Beker & Piper, 1982).
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 ...
Internally, the cipher uses bitwise addition ⊕ (exclusive OR), 32-bit addition mod 2 32 ⊞, and constant-distance rotation operations <<< on an internal state of sixteen 32-bit words. Using only add-rotate-xor operations avoids the possibility of timing attacks in software implementations. The internal state is made of sixteen 32-bit words ...
A large number of block ciphers use the scheme, including the US Data Encryption Standard, the Soviet/Russian GOST and the more recent Blowfish and Twofish ciphers. In a Feistel cipher, encryption and decryption are very similar operations, and both consist of iteratively running a function called a "round function" a fixed number of times.
The number of full cycles depends on the block size, but there are at least six (rising to 32 for small block sizes). The original Block TEA applies the XTEA round function to each word in the block and combines it additively with its leftmost neighbour. Slow diffusion rate of the decryption process was immediately exploited to break the cipher.
In cryptography, the Tiny Encryption Algorithm (TEA) is a block cipher notable for its simplicity of description and implementation, typically a few lines of code.It was designed by David Wheeler and Roger Needham of the Cambridge Computer Laboratory; it was first presented at the Fast Software Encryption workshop in Leuven in 1994, and first published in the proceedings of that workshop.
Some ciphers, such as Rijndael (AES) and Blowfish, use the same operations as those used in the data path of the cipher algorithm for their key expansion, sometimes initialized with some "nothing-up-my-sleeve numbers". Other ciphers, such as RC5, expand keys with functions that are somewhat or completely different from the encryption functions.