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The block transformation f, which is Keccak-f[1600] for SHA-3, is a permutation that uses XOR, AND and NOT operations, and is designed for easy implementation in both software and hardware. It is defined for any power-of-two word size, w = 2 ℓ bits. The main SHA-3 submission uses 64-bit words, ℓ = 6.
The IV is a fixed value (algorithm- or implementation-specific). For each message block, the compression (or compacting) function f takes the result so far, combines it with the message block, and produces an intermediate result. The last block is padded with zeros as needed and bits representing the length of the entire message are appended.
The core block transformation combines 16 words of input with 16 working variables, but only 8 words (256 or 512 bits) are preserved between blocks. It uses a table of 16 constant words (the leading 512 or 1024 bits of the fractional part of π), and a table of 10 16-element permutations:
SHA-0: 1993 NSA: SHA-0: SHA-1: 1995 SHA-0: Specification: SHA-256 SHA-384 SHA-512: 2002 SHA-224: 2004 SHA-3 (Keccak) 2008 Guido Bertoni Joan Daemen Michaël Peeters Gilles Van Assche: RadioGatún: Website Specification: Streebog: 2012 FSB, InfoTeCS JSC RFC 6986: Tiger: 1995 Ross Anderson Eli Biham: Website Specification: Whirlpool: 2004 Vincent ...
A block cipher uses blocks as an unvarying transformation. Even a secure block cipher is suitable for the encryption of only a single block of data at a time, using a fixed key. A multitude of modes of operation have been designed to allow their repeated use in a secure way to achieve the security goals of confidentiality and authenticity.
A block cipher by itself is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of bits called a block. [2] A mode of operation describes how to repeatedly apply a cipher's single-block operation to securely transform amounts of data larger than a block. [3] [4] [5]
SHA-2: A family of two similar hash functions, with different block sizes, known as SHA-256 and SHA-512. They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words. There are also truncated versions of each standard, known as SHA-224, SHA-384, SHA-512/224 and SHA-512/256. These were also designed by the NSA.
The padding appends a 1 bit, followed by as many 0 bits as necessary to make a complete block. Each block is inputted by XORing to the first b bytes of the state, and then performing r rounds of transformation. Finally, 1 is XORed to the state word [11111], and then f rounds of transformation are performed.