SHA512/224 Hash Generator

About

SHA-2 is a set of cryptographic hash functions designed to provide security in online communications. The functions are built using the Merkle-Damgård construction, which makes them resistant to attacks.

SHA-2 includes more significant changes from SHA-1 than its predecessor. The SHA-2 family consists of six hash functions, which create digests (hash values) that are 224, 256, 384, or 512 bits long: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and SHA-512/256. SHA-256 and SHA-512 are hash functions that use 32-bit and 64-bit words respectively. They have different shift amounts and additive constants, but their structures are similar. The only difference is the number of rounds. The SHA-224 and SHA-384 algorithms are truncated versions of the SHA-256 and SHA-512 algorithms respectively, with different initial values. SHA-512/224 and SHA-512/256 are also truncated versions of the SHA-512 algorithm, but with different initial values generated using the Federal Information Processing Standards (FIPS) PUB 180-4 method.

SHA-2 was first published as a U.S. federal standard (FIPS) by the National Institute of Standards and Technology (NIST). The SHA-2 family of algorithms are patented in US, but the United States has released the patent under a royalty-free license.

As of 2011, the best public attacks can break preimage resistance for SHA-256 with 52 out of 64 rounds, or for SHA-512 with 57 out of 80 rounds. Collision resistance can also be broken for SHA-256 with 46 out of 64 rounds.

With the publication of FIPS PUB 180-2, NIST added three additional hash functions in the SHA family. The algorithms are collectively known as SHA-2, named after their digest lengths (in bits): SHA-256, SHA-384, and SHA-512.

The algorithms were first published in 2001 in the draft FIPS PUB 180-2. In August 2002, FIPS PUB 180-2 became the new Secure Hash Standard, replacing FIPS PUB 180-1, which was released in April 1995. The updated standard included the original SHA-1 algorithm, with updated technical notation consistent with that describing the inner workings of the SHA-2 family.

A change notice was published in February 2004 for FIPS PUB 180-2, specifying an additional variant, SHA-224. This variant was defined to match the key length of two-key Triple DES. In October 2008, the standard for FIPS PUB 180-3 was updated to include SHA-224 from the change notice. There were no other fundamental changes made to the standard. The main reason for updating the standard was to move information about hash algorithms and recommendations for using them to Special Publications 800-107 and 800-57. The standard no longer includes detailed test data and example message digests. These are now provided in separate documents.

NIST published SP800-131A in January 2011, which specified a move from 80-bit security (provided by SHA-1) to 112-bit security (provided by SHA-2) as the minimum requirement (starting in 2014) and the recommended security level (starting from the publication date in 2011).

In March 2012, the standard for FIPS PUB 180-4 was updated to include the hash functions SHA-512/224 and SHA-512/256, as well as a method for generating initial values for truncated versions of SHA-512. A restriction on padding the input data prior to hash calculation was removed, allowing hash data to be calculated simultaneously with content generation, such as a real-time video or audio feed. The final data block must still be padded before the hash output.

NIST revised SP800-57 in July 2012 in order to provide guidance for cryptographic key management. The publication does not allow digital signatures with a hash security of less than 112 bits to be created after 2013. NIST revised SP800-107 in 2007 to specify the cutoff to be the end of 2010. In August 2012, NIST revised SP800-107 in the same manner.

In 2012, the NIST hash function competition selected a new hash function, SHA-3. SHA-3 is not derived from SHA-2.