SHA-512/224 and SHA-512/256 are also truncated versions of SHA-512, but the initial values are generated using the method described in Federal Information Processing Standards (FIPS) PUB 180-4. SHA-224 and SHA-384 are truncated versions of SHA-256 and SHA-512 respectively, computed with different initial values. They use different shift amounts and additive constants, but their structures are otherwise virtually identical, differing only in the number of rounds. SHA-256 and SHA-512 are novel hash functions computed with eight 32-bit and 64-bit words, respectively. SHA-2 includes significant changes from its predecessor, SHA-1. 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-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. By guessing the hidden part of the state, length extension attacks on SHA-224 and SHA-384 succeed with probability 2 −(256−224) = 2 −32 > 2 −224 and 2 −(512−384) = 2 −128 > 2 −384 respectively. SHA-256 and SHA-512 are prone to length extension attacks. Pseudo-collision attack against up to 46 rounds of SHA-256. Merkle–Damgård construction with Davies–Meyer compression functionĪ 2011 attack breaks preimage resistance for 57 out of 80 rounds of SHA-512, and 52 out of 64 rounds for SHA-256.
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