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SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. [3] [4] They are built using the Merkle–Damgård construction, from a one-way compression function itself built using the Davies–Meyer structure from a specialized block cipher.
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. SHA-3: A hash function formerly called Keccak, chosen in 2012 after a public competition among non-NSA designers ...
Paul Hsieh's SuperFastHash [1] 32 bits Buzhash: variable XOR/table Fowler–Noll–Vo hash function (FNV Hash) 32, 64, 128, 256, 512, or 1024 bits xor/product or product/XOR Jenkins hash function: 32 or 64 bits XOR/addition Bernstein's hash djb2 [2] 32 or 64 bits shift/add or mult/add or shift/add/xor or mult/xor PJW hash / Elf Hash: 32 or 64 bits
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity. [1]
The following tables compare general and technical information for a number of cryptographic hash functions. See the individual functions' articles for further information. This article is not all-inclusive or necessarily up-to-date. An overview of hash function security/cryptanalysis can be found at hash function security summary.
SHA-256 hash function. Smart contracts use 256- or 257-bit integers; 256-bit words for the Ethereum Virtual Machine. "We realize that a 257 bits byte is quite unusual, but for smart contracts it is ok to have at least 256 bits numbers. The leading VM for smart contracts, Ethereum VM, introduced this practice and other blockchain VMs followed." [8]
SHA-3 uses the pattern 10...01 in its padding function: a 1 bit, followed by zero or more 0 bits (maximum r − 1) and a final 1 bit. The maximum of r − 1 zero bits occurs when the last message block is r − 1 bits long. Then another block is added after the initial 1 bit, containing r − 1 zero bits before the final 1 bit.
In ANSI X9.23, between 1 and 8 bytes are always added as padding. The block is padded with random bytes (although many implementations use 00) and the last byte of the block is set to the number of bytes added. [6] Example: In the following example the block size is 8 bytes, and padding is required for 4 bytes (in hexadecimal format)