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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.
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-2 basically consists of two hash algorithms: SHA-256 and SHA-512. SHA-224 is a variant of SHA-256 with different starting values and truncated output. SHA-384 and the lesser-known SHA-512/224 and SHA-512/256 are all variants of SHA-512. SHA-512 is more secure than SHA-256 and is commonly faster than SHA-256 on 64-bit machines such as AMD64.
10 BLAKE3: Unlimited [note 4] 256 [note 5] 512 64 32 7 GOST: 256 256 256 256 32 32 HAVAL: 256/224/192/160/128 256 1024 64 32 3/4/5 MD2: 128 384 128 – 32 18 MD4: 128 128 512 64 32 3 MD5: 128 128 512 64 32 64 PANAMA: 256 8736 256 – 32 – RadioGatún: Unlimited [note 6] 58 words 19 words [note 7] – 1–64 [note 8] 18 [note 9] RIPEMD: 128 ...
This is especially true of cryptographic hash functions, which may be used to detect many data corruption errors and verify overall data integrity; if the computed checksum for the current data input matches the stored value of a previously computed checksum, there is a very high probability the data has not been accidentally altered or corrupted.
The physical phenomena on which the device relies (such as spinning platters in a hard drive) will also impose limits; for instance, no spinning platter shipping in 2009 saturates SATA revision 2.0 (3 Gbit/s), so moving from this 3 Gbit/s interface to USB 3.0 at 4.8 Gbit/s for one spinning drive will result in no increase in realized transfer rate.
Because of the successful attacks on MD5, SHA-0 and SHA-1, [19] [20] NIST perceived a need for an alternative, dissimilar cryptographic hash, which became SHA-3. After a setup period, admissions were to be submitted by the end of 2008. Keccak was accepted as one of the 51 candidates. In July 2009, 14 algorithms were selected for the second round.
One simple fix is defined in Certificate Transparency: when computing leaf node hashes, a 0x00 byte is prepended to the hash data, while 0x01 is prepended when computing internal node hashes. [13] Limiting the hash tree size is a prerequisite of some formal security proofs , and helps in making some proofs tighter.