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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-2: A family of two similar hash functions, with different block sizes, known as SHA-256 and SHA-512. 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.
The sender is required to find a message whose hash value begins with a number of zero bits. The average work that the sender needs to perform in order to find a valid message is exponential in the number of zero bits required in the hash value, while the recipient can verify the validity of the message by executing a single hash function.
RFC 4635 was circulated to allow RFC 3174 Secure Hash Algorithm (SHA1) hashing and FIPS PUB 180-2 SHA-2 hashing to replace MD5. The 160-bit and 256-bit digests generated by SHA1 and SHA-2 are more secure than the 128-bit digest generated by MD5. RFC 2930 defines TKEY, a DNS record used to distribute keys automatically from a DNS server to DNS ...
[12] [10] [13] NIST formally deprecated use of SHA-1 in 2011 and disallowed its use for digital signatures in 2013, and declared that it should be phased out by 2030. [14] As of 2020, chosen-prefix attacks against SHA-1 are practical. [6] [8] As such, it is recommended to remove SHA-1 from products as soon as possible and instead use SHA-2 or ...
Even though MD2 is not yet fully compromised, the IETF retired MD2 to "historic" status in 2011, citing "signs of weakness". It is deprecated in favor of SHA-256 and other strong hashing algorithms. [4] Nevertheless, as of 2014, it remained in use in public key infrastructures as part of certificates generated with MD2 and RSA. [citation needed]
Because most users typically choose short passwords formed in predictable ways, passwords can often be recovered from their hashed value if a fast hash is used. Searches on the order of 100 billion tests per second are possible with high-end graphics processors.
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