The Secure Hash Algorithm (SHA) is one of a number of cryptographic hash functions published by the National Institute of Standards and Technology (NIST) as a U.S. Federal Information Processing Standard. There are currently three generations of Secure Hash Algorithm. SHA-1 is the original 160-bit hash function which resembles the earlier MD5 algorithm that was designed by the National Security Agency (NSA) to be part of the Digital Signature Algorithm. The algorithm was first published under the name SHA, but was withdrawn shortly after publication due to an undisclosed "significant flaw" and replaced by the slightly revised version SHA-1. The original withdrawn algorithm is now known as SHA-0. SHA-2 is a family of two similar hash functions known as SHA-256 and SHA-512. They both use the same algorithm, but have different block and word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words. The original message will be split into blocks and words will be generated from these blocks as part of the algorithm. There are also truncated versions of each standard, known as SHA-224 and SHA-384. The whole SHA-2 family was also designed by the NSA to fix potential security flaws identified in SHA-1.